Two large case control studies and numerous subsequent analyses were performed to evaluate correlations between brain tumors (identified from cancer registries of the Regional Oncology Center in Sockholm and Uppsala-Orebro regions ) and mobile phone use. In an initial report of 209 cases + 425 controls with brain tumors (recorded January 1997 to June 2000), the authors reported no significant increase in tumor incidence (either malignant or benign) with either analogue or digital cellular telephone exposure [GSM+NMT] OR=0.98; 95%CI 0.69-1.41), [GSM only] OR=0.96; [NMT only] OR=0.93). The authors did report an association between NMT (but not GSM) exposure and ipsilateral tumors using a multivariate analysis (OR=2.45). In subsequent papers, an expanded analysis was performed that included 1617 additional brain tumor cases and employed different statistical methods. In these studies, a significant association was reported for NMT use and benign acoustic neuromas (OR 4.4, 95% CI=2.1-9.2), but not with malignant tumors, and no associations were found between benign or malignant tumors and GSM use. These initial studies also reported an association between NMT use and total brain tumors (OR 1.3, 95% CI 1.04-1.6), although this was mainly due to the influence of the elevated benign tumors (analyzed separately there was no association between NMT use and malignant tumors alone). With further evaluation, ipsilateral brain tumors were found associated with NMT use (OR 1.7, 95% CI 1.2-2.3) as well as with GSM (OR 1.3, 95% CI 1.02-1.8) use. In subsequent papers with more re-analysis, ipsilateral astrocytomas (malignant tumors) were now found correlated with NMT use (OR=1.8, 95% CI 1.1-3.2), as well as with GSM use (OR=1.8, 95% CI=1.1-2.8), and cordless phone use (OR=1.8, 95% CI=1.1-2.9). Ipsilateral tumors located specifically in the temporal area of the brain were correlated even stronger with NMT use (OR=2.3, 95% CI=1.2-4.1). Mobile phone use on the opposite (contralateral) side of the brain was not associated with increased risk for any type of brain tumor. The authors also reported a shorter ipsilateral tumor induction period with exposure than for contralateral tumors, and hypothesized a tumor promoting effect of mobile phones. In another study (Neuroepidemiology, 2003, 22: 124-129), the same study group was further analyzed and the authors reported an association between analogue mobile phone use and vestibular schwannoma (OR 3.45, 95% CI 1.77-6.76). The vestibular schwannoma findings were suggested to correlate with reports by Oftedal et al and Sandstrom et al of increased complaints of tinnitus (a precondition of vestibular schwannoma) with mobile phone use in Norway, and a subsequent report by the authors described 3 additional cases of mobile phone users complaining of tinnitus that "contacted" them. A subsequent report (Occupational Environmental Medicine (2004) 61(8):675-9) using the same protocol and cancer registry reported no association between mobile or cordless phone use and salivary gland tumors, although the scarcity of this tumor type (only 0.2 percent tumors reported to the Swedish cancer registry in 2001) made statistical evaluation difficult. Another subsequent study (Occup Environ Med (2005) 62:390-394) looked at the same cases used above for correlations between brain tumors and urban (n=984 cases, 1035 controls) vs. rural (n=445 cases, n=435 controls) mobile phone use. The authors report a general correlation between total risk for all (malignant + benign) brain tumors and NMT analogue mobile phone use in urban (OR = 1.5; 95% CI 0.9 - 2.6) and rural (OR = 1.9; 95% CI 0.9 - 3.9) areas. For ipsilateral brain tumors (same side as mobile phone use) with a > 1 year latency, there was a slightly stronger correlation with analogue mobile phone use in urban areas (OR=1.7; 95% CI 1.1-2.5). A stronger correlation existed for ipsilateral brain tumors with a >5 year tumor latency and > 55 hours on the phone and rural residence (OR = 4.2; 95% CI 1.1-16). Associations between digital (GSM) phone and malignant brain tumors were higher for rural users than for urban users, especially when only ipsilateral tumors were considered (rural OR = 3.2; 95% CI 1.2 - 8.4 vs. urban OR = 0.9; 95% CI 0.6 - 1.4). When malignant brain tumors having >5 year tumor latency were considered, digital (GSM) mobile phone use in rural areas (OR=8.4; 95% CI 1.02-69) was more highly correlated than with urban use (OR = 1.4; 95% CI 0.8 - 2.6). The authors suggest that higher average transmit power of mobile phones in rural areas (presumably due to weaker receive signal from less dense base station sites and corresponding higher handset power) is responsible for increased correlations in rural areas. When 2000+ hrs of cumulative use was considered, OR = 5.9; 95% CI 2.5-14 for analog, OR = 3.7; 95% CI 1.7-7.7 for digital, and OR = 2.3; 95% CI 1.5-3.6 for cordless phone use. Additional reports (Neuroepidemiology 2005, 25:120-128) analyzed correlations between mobile and cordless phone use and various benign brain tumors (including 305 meningioma cases, 84 acoustic neuroma cases, 24 other benign tumor types, and 692 controls) in more detail. The authors report correlations between meningioma with a 10 year latency period and analogue mobile phone use (OR = 2.1; 95% CI = 1.1-4.3) as well as acoustic neuroma with analogue (OR = 4.2; 95% CI = 1.8-10) and digital (OR = 2.0; 95% CI = 1.05-3.8) mobile phone use. The risk between analogue mobile phone use and acoustic neuroma increased when a >15-year latency period was considered (OR = 8.4; 95% CI = 1.6-45) although this was based on low numbers. In a recent study (Environ Res 2005), the authors report additional data from malignant brain tumor cases (n = 317 + 692 controls) and report correlations with analogue mobile phone use (OR = 2.6; 95% CI 1.5 4.3, increasing to OR= 3.5; 95% CI 2.0 6.4 with a >10-year latency period) and digital mobile phone use (OR= 1.9; 95% CI = 1.3 2.7, increasing to OR = 3.6; 95% CI = 1.7 7.5 with a >10-year latency period). Correlations with cordless telephone use were also reported (OR = 2.1; 95% CI = 1.4 3.0, increasing to OR = 2.9; 95% CI = 1.6 5.2 with a >10-year latency period). The strongest correlation was with high grade astrocytoma. In a recent study reported in Int Arch Environ Health (2005) using the same questionnaire based exposure assessment and the same Swedish cancer registry population pool, the authors examine possible correlations with lymphoma (n = 910; 819 B-cell NHL, 53 T-cell NHL, 38 unspecified). They perform many different analyses and divide / stratify cases and controls by phone type, cancer sub-type, etc. They report no correlation between either NMT/analogue and GSM/digital mobile phone use and B-cell NHL, but a statistically significant correlation with T-cell NHL (OR = 2.47; 95% CI 1.09-5.60) based on 17 cases. They also report a correlation with cordless phone use for more than 10 years (OR = 3.15; 95% CI 1.05 - 9.48) based on 6 cases. Other correlations with stratified groups were also reported. In an earlier study (Epidemiology, 1999, 10:785-786) the authors reported angiosarcoma of the scalp associated with use of cordless telephones. An earlier report (Int. J. Oncol. 1998, 13:1299-1303 also reported possible associations between testicular cancer and amateur radio operators (OR 2.2; CI 0.7-6.6), work with radar equipment (OR 2.0; CI 0.3-14.2) and engineers in electronics and telecommunication industry (OR 2.3; CI 0.8-6.7), but this was based on very few exposed subjects. A review article was also reported by the authors (European J Cancer Prevention (2005) 14(3):285-288) describing their rationale and methods for combining different types of wireless phone (analog, cordless, GSM digital) to reflect an individual's RF exposure over time. A subsequent paper (Int J Oncol 2006) reported on the collective / pooled analysis from all of the tumor cases obtained between 1997 2003, which involved two separate case control studies with 1,254 cases / 2,162 controls and substantial analysis / reanalysis of the data. In this paper, the authors report correlations between acoustic neuroma and analogue mobile phone (OR = 2.9; 95% CI 2.0-4.3), GSM mobile phone (OR=1.5; 95% CI=1.1-2.1), and cordless telephone (OR=1.5, 95% CI=1.04-2.0) use. Analogue mobile phone use for >15 years gave the highest correlation (OR=3.8, 95% CI=1.4-10). The authors also report correlations between meningioma (a form of glioma) and analogue mobile phone (OR=1.3, 95% CI=0.99-1.7), GSM mobile phone (OR=1.1, 95% CI=0.9-1.3), and cordless telephone (OR=1.1, 95% CI=0.9-1.4) use. In particular, the authors identify that their reports on correlations between mobile phone exposure and iplilateral glial are supported by recent INTERPHONE reports, particularly the Hepworth et al 2006 paper. Three subsequent papers on meta-analysis of previously published studies (2 cohort + 16 case control) were performed (2007, 2008,, 2009) on 2946 brain tumors and the authors report the following: OR = 0.9; 95% CI 0.8-1.1 overall glioma, OR = 1.2; 95% CI 0.8-1.9 10+yr glioma, OR = 2.0; 95% CI 1.2-3.4 10+yr / ipsilateral glioma (4 studies total), OR = 0.9; 95% CI 0.7-1.1 overall acoustic neuroma, OR = 1.3; 95% CI 0.6-2.8 10+ yr acoustic neuroma, OR = 2.4; 95% CI 1.1-5.3 10+ yr / ipsilateral acoustic neuroma. In a set of earlier papers, the authors report no effects on testicular cancer with either mobile or cordless phone use. Although not yet published, the authors announced in a meeting organized by the Radiation Research Trust an increased correlation specifically between astrocytoma (OR = 1.4; 95% CI = 1.1-1.7) that increased with ipsilateral (OR = 2.0; 95% CI = 1.5-2.5), 10+ yr use (OR = 3.3; 95% CI = 2.0-5.4), and use prior to the age of 20 (OR = 5.2; 95% CI= 2.2-12.0). In a 2009 report, the authors evaluated 905 malignant brain tumor cases, 1254 benign brain tumor cases, and 2162 controls and reported OR = 1.4; 95% CI 1.1-1.7 for overall astrocytoma (grade I-IV), OR = 20; 95% CI 1.5-2.5 for ipsilateral astrocytoma (grade I-IV), and OR = 1.0; 95% CI 0.7-1.4 for contralateral astrocytoma (grade I-IV), OR = 2.7; 95% CI 1.8-3.9 for 10+yr astrocytoma, OR = 3.3; 95% CI 2.0-5.4 for ipsilateral astrocytoma, and OR = 2.8 (95% CI 1.5-5.1 contralateral astrocytoma. For cordless phones, OR = 1.4; 95% CI 1.1-1.8 for overall astrocytoma, OR = 1.8; 95% CI 1.4-2.4 for ipsilateral astrocytoma, and OR = 1.2 ; 95% CI 0.8-1.6 for contralateral astrocytoma, OR = 2.5 ; 95% CI 1.4-4.4 for 10+yr astrocytoma, OR = 5.0; 95% CI 2.3-11 for 10+yr ipsilateral astrocytoma, OR = 1.4; 95% CI 0.6-3.5 for 10+yr contralateral astrocytoma. ORs analyzed separately by age group was highest for age group < 20 years than for age group 20-49 or 50-80 (e.g. OR = 7.8; 95% CI 2.2-28 for <20 yrs ipsilateral astrocytoma vs OR = 2.1; 95% CI 1.5-2.9 for 20-49 ipsilateral astrocytoma and OR = 1.8; 95% CI 1.3-2.5 for 50-80 ipsilateral astrocytoma. The pattern for cordless phones was similar (OR = 7.9; 95% CI 2.5-25), OR = 1.6; 95% CI 1.1-2.4, and OR = 1.9; 95% CI 1.3-2.7, respectively. No significant risk was found for oligodendroglioma or other/mixed gliomas. For mobile phones and acoustic neuroma, the pattern was similar to astrocytoma (OR =6.8; 95% CI 1.4-34 for < 20 years ipsilateral acoustic neuroma, OR = 2.5; 95% CI 1.6-3.9 for 20-49 yr ipsilateral acoustic neuroma, and OR = 1.1; 95% CI 0.6-1.9 for 50-80 yr ipsilateral acoustic neuroma). For cordless phones and acoustic neuroma the trend was similar to that with mobile phones (OR = 1.7; 95% CI 0.2-16), OR = 2.2; 95% CI 1.4-3.6, and OR = 1.3; 95% CI = 0.7-2.2).
Authors' abstract: Hardell et al. 2011:
We studied the association between use of mobile and cordless phones and malignant brain tumours. Pooled analysis was performed of two case-control studies on patients with malignant brain tumours diagnosed during 1997-2003 and matched controls alive at the time of study inclusion and one case-control study on deceased patients and controls diagnosed during the same time period. Cases and controls or relatives to deceased subjects were interviewed using a structured questionnaire. Replies were obtained for 1,251 (85%) cases and 2,438 (84%) controls. The risk increased with latency period and cumulative use in hours for both mobile and cordless phones. Highest risk was found for the most common type of glioma, astrocytoma, yielding in the >10 year latency group for mobile phone use odds ratio (OR) = 2.7, 95% confidence interval (CI) = 1.9-3.7 and cordless phone use OR = 1.8, 95% CI = 1.2-2.9. In a separate analysis, these phone types were independent risk factors for glioma. The risk for astrocytoma was highest in the group with first use of a wireless phone before the age of 20; mobile phone use OR = 4.9, 95% CI = 2.2-11, cordless phone use OR = 3.9, 95% CI = 1.7-8.7. In conclusion, an increased risk was found for glioma and use of mobile or cordless phone. The risk increased with latency time and cumulative use in hours and was highest in subjects with first use before the age of 20.
AUTHORS' ABSTRACT: Soderqvist, Carlberg and Hardell 2012 (IEEE #5165):The last decades of increasing use of wireless phones, including mobile as well as cordless desktop phones, have led to concerns about the potential carcinogenic effects of radiofrequency electromagnetic fields. Among the most exposed areas of the body when the phone is used for talking are the salivary glands, mainly the parotid gland, located in front of the ear. The objective of this case-control study was to assess whether the use of wireless phones is associated with an increased risk of tumour at this site. Sixty-nine patients with salivary gland tumours (63 with a parotid gland tumour) and 262 randomly recruited controls were included. Unconditional logistic regression - adjusted for age at diagnosis, sex, year of diagnosis and socioeconomic index - was used to produce odds ratios and 95% confidence intervals. The use of wireless phones was not associated with an overall increased risk of salivary gland tumours, odds ratio 0.8, 95% confidence interval 0.4-1.5. Neither was there an increased risk for the different phone types when calculated separately nor was there an increased risk for different latencies or when cumulative use was divided into three groups (1-1000, 1001-2000 and >2000 h). The overall results were similar for the risk of parotid gland tumours. In conclusion, our data add to the evidence against there being an increased risk for parotid gland tumours associated with light-to-moderate use of wireless phones and for less than 10 years of use but offers little information on risk related to more prolonged and/or heavy use.
AUTHORS' ABSTRACT: Hardell et al. 2012 (IEEE #5217): The International Agency for Research on Cancer (IARC) at WHO evaluation of the carcinogenic effect of RF-EMF on humans took place during a 24-31 May 2011 meeting at Lyon in France. The Working Group consisted of 30 scientists and categorised the radiofrequency electromagnetic fields from mobile phones, and from other devices that emit similar non-ionising electromagnetic fields (RF-EMF), as Group 2B, i.e., a 'possible', human carcinogen. The decision on mobile phones was based mainly on the Hardell group of studies from Sweden and the IARC Interphone study. We give an overview of current epidemiological evidence for an increased risk for brain tumours including a meta-analysis of the Hardell group and Interphone results for mobile phone use. Results for cordless phones are lacking in Interphone. The meta-analysis gave for glioma in the most exposed part of the brain, the temporal lobe, odds ratio (OR)=1.71, 95% confidence interval (CI)=1.04-2.81 in the e10 years (>10 years in the Hardell group) latency group. Ipsilateral mobile phone use e1640h in total gave OR=2.29, 95% CI=1.56-3.37. The results for meningioma were OR=1.25, 95% CI=0.31-4.98 and OR=1.35, 95% CI=0.81-2.23, respectively. Regarding acoustic neuroma ipsilateral mobile phone use in the latency group e10 years gave OR=1.81, 95% CI=0.73-4.45. For ipsilateral cumulative use e1640h OR=2.55, 95% CI=1.50-4.40 was obtained. Also use of cordless phones increased the risk for glioma and acoustic neuroma in the Hardell group studies. Survival of patients with glioma was analysed in the Hardell group studies yielding in the >10 years latency period hazard ratio (HR)=1.2, 95% CI=1.002-1.5 for use of wireless phones. This increased HR was based on results for astrocytoma WHO grade IV (glioblastoma multiforme). Decreased HR was found for low-grade astrocytoma, WHO grades I-II, which might be caused by RF-EMF exposure leading to tumour-associated symptoms and earlier detection and surgery with better prognosis. Some studies show increasing incidence of brain tumours whereas other studies do not. It is concluded that one should be careful using incidence data to dismiss results in analytical epidemiology. The IARC carcinogenic classification does not seem to have had any significant impact on governments' perceptions of their responsibilities to protect public health from this widespread source of radiation.
AUTHORS' ABSTRACT: Hardell et al. 2013 (IEEE #5273): We previously conducted a case-control study of acoustic neuroma. Subjects of both genders aged 20-80 years, diagnosed during 1997-2003 in parts of Sweden, were included, and the results were published. We have since made a further study for the time period 2007-2009 including both men and women aged 18-75 years selected from throughout the country. These new results for acoustic neuroma have not been published to date. Similar methods were used for both study periods. In each, one population-based control, matched on gender and age (within five years), was identified from the Swedish Population Registry. Exposures were assessed by a self-administered questionnaire supplemented by a phone interview. Since the number of acoustic neuroma cases in the new study was low we now present pooled results from both study periods based on 316 participating cases and 3,530 controls. Unconditional logistic regression analysis was performed, adjusting for age, gender, year of diagnosis and socio-economic index (SEI). Use of mobile phones of the analogue type gave odds ratio (OR) = 2.9, 95% confidence interval (CI) = 2.0-4.3, increasing with >20 years latency (time since first exposure) to OR = 7.7, 95% CI = 2.8-21. Digital 2G mobile phone use gave OR = 1.5, 95% CI = 1.1-2.1, increasing with latency >15 years to an OR = 1.8, 95% CI = 0.8-4.2. The results for cordless phone use were OR = 1.5, 95% CI = 1.1-2.1, and, for latency of >20 years, OR = 6.5, 95% CI = 1.7-26. Digital type wireless phones (2G and 3G mobile phones and cordless phones) gave OR = 1.5, 95% CI = 1.1-2.0 increasing to OR = 8.1, 95% CI = 2.0-32 with latency >20 years. For total wireless phone use, the highest risk was calculated for the longest latency time >20 years: OR = 4.4, 95% CI = 2.2-9.0. Several of the calculations in the long latency category were based on low numbers of exposed cases. Ipsilateral use resulted in a higher risk than contralateral for both mobile and cordless phones. OR increased per 100 h cumulative use and per year of latency for mobile phones and cordless phones, though the increase was not statistically significant for cordless phones. The percentage tumour volume increased per year of latency and per 100 h of cumulative use, statistically significant for analogue phones. This study confirmed previous results demonstrating an association between mobile and cordless phone use and acoustic neuroma.
AUTHORS' ABSTRACT: Carlberg et al. 2013 (IEEE #5274): BACKGROUND: To study the association between use of wireless phones and meningioma.
METHODS:We performed a case--control study on brain tumour cases of both genders aged 18--75 years and diagnosed during 2007--2009. One population-based control matched on gender and age was used to each case. Here we report on meningioma cases including all available controls. Exposures were assessed by a questionnaire. Unconditional logistic regression analysis was performed.
RESULTS: In total 709 meningioma cases and 1,368 control subjects answered the questionnaire. Mobile phone use in total produced odds ratio (OR) = 1.0, 95% confidence interval (CI) = 0.7-1.4 and cordless phone use gave OR = 1.1, 95% CI = 0.8-1.5. The risk increased statistically significant per 100 h of cumulative use and highest OR was found in the fourth quartile (>2,376 hours) of cumulative use for all studied phone types. There was no statistically significant increased risk for ipsilateral mobile or cordless phone use, for meningioma in the temporal lobe or per year of latency. Tumour volume was not related to latency or cumulative use in hours of wireless phones.
CONCLUSIONS:No conclusive evidence of an association between use of mobile and cordless phones and meningioma was found. An indication of increased risk was seen in the group with highest cumulative use but was not supported by statistically significant increasing risk with latency. Results for even longer latency periods of wireless phone use than in this study are desirable.
AUTHORS' ABSTRACT: Hardell et al. 2013 (IEEE #5312). Previous studies have shown a consistent association between long-term use of mobile and cordless phones and glioma and acoustic neuroma, but not for meningioma. When used these phones emit radiofrequency electromagnetic fields (RF-EMFs) and the brain is the main target organ for the handheld phone. The International Agency for Research on Cancer (IARC) classified in May, 2011 RF-EMF as a group 2B, i.e. a 'possible' human carcinogen. The aim of this study was to further explore the relationship between especially long-term (>10 years) use of wireless phones and the development of malignant brain tumours. We conducted a new case-control study of brain tumour cases of both genders aged 18-75 years and diagnosed during 2007-2009. One population-based control matched on gender and age (within 5 years) was used to each case. Here, we report on malignant cases including all available controls. Exposures on e.g. use of mobile phones and cordless phones were assessed by a self-administered questionnaire. Unconditional logistic regression analysis was performed, adjusting for age, gender, year of diagnosis and socio-economic index using the whole control sample. Of the cases with a malignant brain tumour, 87% (n=593) participated, and 85% (n=1,368) of controls in the whole study answered the questionnaire. The odds ratio (OR) for mobile phone use of the analogue type was 1.8, 95% confidence interval (CI)=1.043.3, increasing with >25 years of latency (time since first exposure) to an OR=3.3, 95% CI=1.6-6.9. Digital 2G mobile phone use rendered an OR=1.6, 95% CI=0.996-2.7, increasing with latency >15-20 years to an OR=2.1, 95% CI=1.2-3.6. The results for cordless phone use were OR=1.7, 95% CI=1.1-2.9, and, for latency of 15-20 years, the OR=2.1, 95% CI=1.2-3.8. Few participants had used a cordless phone for >20-25 years. Digital type of wireless phones (2G and 3G mobile phones, cordless phones) gave increased risk with latency >1-5 years, then a lower risk in the following latency groups, but again increasing risk with latency >15-20 years. Ipsilateral use resulted in a higher risk than contralateral mobile and cordless phone use. Higher ORs were calculated for tumours in the temporal and overlapping lobes. Using the meningioma cases in the same study as reference entity gave somewhat higher ORs indicating that the results were unlikely to be explained by recall or observational bias. This study confirmed previous results of an association between mobile and cordless phone use and malignant brain tumours. These findings provide support for the hypothesis that RF-EMFs play a role both in the initiation and promotion stages of carcinogenesis.
AUTHORS' ABSTRACT: Hardell and Carlberg 2013 (IEEE #5388): Wireless phones, i.e., mobile phones and cordless phones, emit radiofrequency electromagnetic fields (RF-EMF) when used. An increased risk of brain tumors is a major concern. The International Agency for Research on Cancer (IARC) at the World Health Organization (WHO) evaluated the carcinogenic effect to humans from RF-EMF in May 2011. It was concluded that RF-EMF is a group 2B, i.e., a "possible", human carcinogen. Bradford Hill gave a presidential address at the British Royal Society of Medicine in 1965 on the association or causation that provides a helpful framework for evaluation of the brain tumor risk from RF-EMF. Methods: All nine issues on causation according to Hill were evaluated. Regarding wireless phones, only studies with long-term use were included. In addition, laboratory studies and data on the incidence of brain tumors were considered. Results: The criteria on strength, consistency, specificity, temporality, and biologic gradient for evidence of increased risk for glioma and acoustic neuroma were fulfilled. Additional evidence came from plausibility and analogy based on laboratory studies. Regarding coherence, several studies show increasing incidence of brain tumors, especially in the most exposed area. Support for the experiment came from antioxidants that can alleviate the generation of reactive oxygen species involved in biologic effects, although a direct mechanism for brain tumor carcinogenesis has not been shown. In addition, the finding of no increased risk for brain tumors in subjects using the mobile phone only in a car with an external antenna is supportive evidence. Hill did not consider all the needed nine viewpoints to be essential requirements. Conclusion: Based on the Hill criteria, glioma and acoustic neuroma should be considered to be caused by RF-EMF emissions from wireless phones and regarded as carcinogenic to humans, classifying it as group 1 according to the IARC classification. Current guidelines for exposure need to be urgently revised.
AUTHORS' ABSTRACT: Hardell and Carlberg 2013 (IEEE #5477). BACKGROUND: We analysed the survival of patients after glioma diagnosis in relation to the use of wireless phones.
METHODS: All cases diagnosed between 1997 and 2003 with a malignant brain tumour (n = 1,251) in our case-control studies were included and followed from the date of diagnosis to the date of death or until May 30, 2012.
RESULTS: For glioma, the use of wireless phones (mobile and cordless phones) gave a hazard ratio (HR) = 1.1 (95% confidence interval, CI = 0.9-1.2), with > 10-year latency HR = 1.2 (95% CI = 1.002-1.5, p trend = 0.02). For astrocytoma grade I-II (low-grade), the results were, HR = 0.5 (95% CI = 0.3-0.9) and for astrocytoma grade IV (glioblastoma), HR = 1.1 (95% CI = 0.95-1.4), with > 10 year latency HR = 1.3 (95% CI = 1.03-1.7). In the highest tertile (> 426 h) of cumulative use, HR = 1.2 (95% CI = 0.95-1.5) was found for glioblastoma. The results were similar for mobile and cordless phones.
CONCLUSIONS: Decreased survival of glioma cases with long-term and high cumulative use of wireless phones was found. A survival disadvantage for astrocytoma grade IV, but a survival benefit for astrocytoma grade I-II was observed which could be due to exposure-related tumour symptoms leading to earlier diagnosis and surgery in that patient group.
AUTHORS' ABSTRACT: Soderqvist et al. 2011 (IEEE #5652): Case-control studies on adults point to an increased risk of brain tumours (glioma and acoustic neuroma) associated with the long-term use of mobile phones. Recently, the first study on mobile phone use and the risk of
brain tumours in children and adolescents, CEFALO, was published. It has been claimed that this relatively small study yielded reassuring results of no increased risk. We do not agree. We consider that the data contain several indications of increased risk, despite low exposure, short latency period, and limitations in the study design, analyses and interpretation. The information certainly cannot be used as reassuring evidence against an association,
for reasons that we discuss in this commentary.
AUTHORS' ABSTRACT: Hardell and Carlberg 2014 (IEEE #5803): We made a pooled analysis of two case-control studies on malignant brain tumours with patients diagnosed during 19972003 and20072009. They were aged 2080 years and 1875 years, respectively, at the time of diagnosis. Only cases with histopathological verification of the tumour were included. Population-based controls, matched on age and gender, were used. Exposures were assessed by questionnaire. The whole reference group was used in the unconditional regression analysis adjusted for gender, age, year of diagnosis, and socio-economic index. In total, 1498 (89%) cases and 3530 (87%) controls participated. Mobile phone use increased the risk of glioma, OR = 1.3, 95%CI = 1.11.6 overall, increasing to OR = 3.0, 95% CI = 1.75.2 in the >25 year latency group. Use of cordless phones increased the risk to OR = 1.4, 95% CI = 1.11.7, with highest risk in the >1520 years latency group yielding OR = 1.7, 95% CI = 1.12.5. The OR increased statistically significant both per 100 h of cumulative use, and per year of latency for mobile and cordless phone use. Highest ORs overall were found for ipsilateral mobile or cordless phone use, OR = 1.8, 95% CI = 1.42.2 and OR = 1.7, 95% CI = 1.32.1, respectively. The highest risk was found for glioma in the temporal lobe. First use of mobile or cordless phone before the age of 20 gave higher OR for glioma than in later age groups.
AUTHORS' ABSTRACT: Carlberg and Hardell 2014 (IEEE #5849): On 31 May 2011 the WHO International Agency for Research on Cancer (IARC)
categorised radiofrequency electromagnetic fields (RF-EMFs) from mobile phones, and from other devices that emit similar non-ionising electromagnetic fields, as a Group 2B, i.e., a possible, human carcinogen. A causal association would be strengthened if it could
be shown that the use of wireless phones has an impact on the survival of glioma patients.
We analysed survival of 1678 glioma patients in our 19972003 and 20072009 case-control studies. Use of wireless phones in the >20 years latency group (time since first use) yielded an increased hazard ratio (HR) = 1.7, 95% confidence interval (CI) = 1.22.3 for glioma. For astrocytoma grade IV (glioblastoma multiforme; n = 926) mobile phone
use yielded HR = 2.0, 95% CI = 1.42.9 and cordless phone use HR = 3.4, 95% CI = 1.0411
in the same latency category. The hazard ratio for astrocytoma grade IV increased statistically
significant per year of latency for wireless phones, HR = 1.020, 95% CI = 1.0071.033,
but not per 100 h cumulative use, HR = 1.002, 95% CI = 0.9991.005. HR was not statistically significant increased for other types of glioma. Due to the relationship with survival the classification of IARC is strengthened and RF-EMF should be regarded as human carcinogen requiring urgent revision of current exposure guidelines.
AUTHORS' ABSTRACT: Hardell and Carlberg 2015 (IEEE #5850): We made a pooled analysis of two case-control studies on malignant brain tumours with patients diagnosed during 19972003 and 20072009. They were aged 2080 years and 1875 years, respectively, at the time of diagnosis. Only cases with histopathological verification of the tumour were included. Population-based controls, matched on age and gender, were used. Exposures were assessed by questionnaire. The whole reference group was used in the unconditional regression analysis adjusted for gender, age, year of diagnosis, and socio-economic index. In total, 1498 (89%) cases and 3530 (87%) controls participated. Mobile phone use increased the risk of glioma, OR=1.3, 95% CI=1.11.6 overall, increasing to OR=3.0, 95% CI=1.75.2 in the >25 year latency group. Use of cordless phones increased the risk to OR=1.4, 95% CI=1.11.7, with highest risk in the >1520 years latency group yielding OR=1.7, 95% CI=1.12.5. The OR increased statistically significant both per 100h of cumulative use, and per year of latency for mobile and cordless phone use. Highest ORs overall were found for ipsilateral mobile or cordless phone use, OR=1.8, 95% CI=1.42.2 and OR=1.7, 95% CI=1.32.1, respectively. The highest risk was found for glioma in the temporal lobe. First use of mobile or cordless phone before the age of 20 gave higher OR for glioma than in later age groups.
AUTHORS' ABSTRACT: Hardell and Carlberg 2015 (IEEE #5934): Radiofrequency emissions in the frequency range 30 kHz-300 GHz were evaluated to be Group 2B, i.e., "possibly", carcinogenic to humans by the International Agency for Research on Cancer (IARC) at WHO in May 2011. The Swedish Cancer Register has not shown increasing incidence of brain tumours in recent years and has been used to dismiss epidemiological evidence on a risk. In this study we used the Swedish National Inpatient Register (IPR) and Causes of Death Register (CDR) to further study the incidence comparing with the Cancer Register data for the time period 1998-2013 using joinpoint regression analysis. In the IPR we found a joinpoint in 2007 with Annual Percentage Change (APC) +4.25%, 95% CI +1.98, +6.57% during 2007-2013 for tumours of unknown type in the brain or CNS. In the CDR joinpoint regression found one joinpoint in 2008 with APC during 2008-2013 +22.60%, 95% CI +9.68, +37.03%. These tumour diagnoses would be based on clinical examination, mainly CT and/or MRI, but without histopathology or cytology. No statistically significant increasing incidence was found in the Swedish Cancer Register during these years. We postulate that a large part of brain tumours of unknown type are never reported to the Cancer Register. Furthermore, the frequency of diagnosis based on autopsy has declined substantially due to a general decline of autopsies in Sweden adding further to missing cases. We conclude that the Swedish Cancer Register is not reliable to be used to dismiss results in epidemiological studies on the use of wireless phones and brain tumour risk.
AUTHORS' ABSTRACT: Soderqvist, Carlberg and Hardell 2015 (IEEE #5936): For some time it has been investigated whether low-intensity non-thermal microwave radiation from mobile phones adversely affects the mammalian bloodbrain barrier (BBB). All such studies except one have been either in vitro or experimental animal studies. The one carried out on humans showed a statistically significant increase in serum transthyretin (TTR) 60 min after finishing of a 30-min microwave exposure session. The aim of the present study was to follow up on the finding of the previous one using a better study design. Using biomarkers analyzed in blood serum before and after the exposure this single blinded randomized counterbalanced study, including 24 healthy subjects aged 1830 years that all underwent three exposure conditions (SAR10G = 2 W/kg, SAR10G = 0.2 W/kg, sham), tested whether microwaves from an 890-MHz phone-like signal give acute effects on the integrity of brain-shielding barriers. Over time, statistically significant variations were found for two of the three biomarkers (TTR; ²-trace protein); however, no such difference was found between the different exposure conditions nor was there any interaction between exposure condition and time of blood sampling. In conclusion this study failed to show any acute clinically or statistically significant effect of short term microwave exposure on the serum levels of S100², TTR and ²-trace protein with a follow up limited to two hours. The study was hampered by the fact that all study persons were regular wireless phone users and thus not naïve as to microwave exposure.
AUTHORS' ABSTRACT: Carlberg and Hardell 2015 (IEEE #6043): A pooled analysis of two case-control studies on meningioma with patients diagnosed during 1997-2003 and 2007-2009 was conducted. Both genders were included, aged 20-80 and 18-75 years, respectively, at the time of diagnosis. Population-based controls, matched according to age and gender, were enrolled. Exposure was assessed by questionnaire. In the entire study, cases with all brain tumor types were included. The whole reference group was used in the unconditional logistic regression analysis on meningioma, with adjustments for gender, age, year of diagnosis and socio-economic index (SEI). In total, 1,625 meningioma cases and 3,530 controls were analyzed. Overall no association with use of mobile or cordless phones was found. In the fourth quartile of use (>1,436 h) somewhat increased risk was found for mobile phones yielding an odds ratio (OR)=1.2, 95% confidence intervals (CI)=0.9-1.6 and cordless phones OR=1.7, 95% CI=1.3-2.2. Higher risk was calculated in the highest decile (>3,358 h), OR=1.5, 95% CI=0.99-2.1 and OR=2.0, 95% CI=1.4-2.8, respectively. In addition, the longest latency time gave somewhat increased risk for both phone types although the result was not statistically significant. There was no association for ipsilateral use or anatomical tumor location. The present study showed a somewhat increased risk among heavy users of mobile and cordless phones. Since meningioma is generally a slow-growing tumor, longer latency period is necessary for definitive conclusions.
AUTHORS' ABSTRACT: Soderqvist, Carlberg, Hardell 2012 (IEEE #6215): BACKGROUND: Since the International Agency for Research on Cancer recently classified radiofrequency electromagnetic fields, such as those emanating from mobile and cordless phones, as possibly carcinogenic to humans (group 2B), two additional reports relevant to the topic have been published. Both articles were new updates of a Danish cohort on mobile phone subscribers and concern the possible association between assumed use of mobile phones and risk of brain tumors. The aim of the present review is to reexamine all four publications on this cohort.
METHODS: In brief, publications were scrutinized, and in particular, if the authors made explicit claims to have either proved or disproved their hypothesis, such claims were reviewed in light of applied methods and study design, and in principle, the stronger the claims, the more careful our review.
RESULTS: The nationwide Danish cohort study on mobile phone subscribers and risk of brain tumors, including at best 420,095 persons (58% of the initial cohort), is the only one of its kind. In comparison with previous investigations, i.e., case-control studies, its strength lies in the possibility to eliminate non-response, selection, and recall bias. Although at least non-response and recall bias can be excluded, the study has serious limitations related to exposure assessment. In fact, these limitations cloud the findings of the four reports to such an extent that render them uninformative at best. At worst, they may be used in a seemingly solid argument against an increased risk--as reassuring results from a large nationwide cohort study, which rules out not only non-response and recall bias but also an increased risk as indicated by tight confidence intervals.
CONCLUSION: Although two of the most comprehensive case-control studies on the matter both have methodological limitations that need to be carefully considered, type I errors are not the only threats to the validity of studies on this topic--the Danish cohort study is a textbook example of that.
AUTHORS' ABSTRACT: Carlberg and Hardell 2012 (IEEE #6231):We performed two case-control studies on brain tumours diagnosed during 1 January 1997 to 30 June 2000 and 1 July 2000 to 31 December 2003, respectively. Living cases and controls aged 20-80 years were included. An additional study was performed on deceased cases with a malignant brain tumour using deceased controls. Pooled results for glioma yielded for ipsilateral use of mobile phone odds ratio (OR)=2.9, 95% confidence interval (CI)=1.8-4.7 in the >10 years latency group. The corresponding result for cordless phone was OR=3.8, 95% CI=1.8-8.1. OR increased statistically significant for cumulative use of wireless phones per 100h and per year of latency. For high-grade glioma ipsilateral use of mobile phone gave OR=3.9, 95% CI=2.3-6.6 and cordless phone OR=5.5, 95% CI=2.3-13 in the >10 years latency group. Heredity for brain tumour gave OR=3.4, 95% CI=2.1-5.5 for glioma. There was no interaction with use of wireless phones. X-ray investigation of the head gave overall OR=1.3, 95% CI=1.1-1.7 for glioma without interaction with use of wireless phones or heredity. In conclusion use of mobile and cordless phone increased the risk for glioma with highest OR for ipsilateral use, latency >10 years and third tertile of cumulative use in hours. In total, the risk was highest in the age group <20 years for first use of a wireless phone.
AUTHORS' SUMMARY: Hardell, Carlberg, Mild 2011 (IEEE #6234): These results confirm our previous findings of an increased risk for malignant brain tumour among mobile phone users.
AUTHORS' ABSTRACT: Carlberg, Hardell et al.
2016 (IEEE #6430): BACKGROUND: Radiofrequency radiation in the frequency range 30 kHz-300 GHz was evaluated to be Group 2B, i.e. 'possibly' carcinogenic to humans, by the International Agency for Research on Cancer (IARC) at WHO in May 2011. Among the evaluated devices were mobile and cordless phones, since they emit radiofrequency electromagnetic fields (RF-EMF). In addition to the brain, another organ, the thyroid gland, also receives high exposure. The incidence of thyroid cancer is increasing in many countries, especially the papillary type that is the most radiosensitive type.
METHODS: We used the Swedish Cancer Register to study the incidence of thyroid cancer during 1970-2013 using joinpoint regression analysis.
RESULTS: In women, the incidence increased statistically significantly during the whole study period; average annual percentage change (AAPC) +1.19 % (95 % confidence interval (CI) +0.56, +1.83 %). Two joinpoints were detected, 1979 and 2001, with a high increase of the incidence during the last period 2001-2013 with an annual percentage change (APC) of +5.34 % (95 % CI +3.93, +6.77 %). AAPC for all men during 1970-2013 was +0.77 % (95 % CI -0.03, +1.58 %). One joinpoint was detected in 2005 with a statistically significant increase in incidence during 2005-2013; APC +7.56 % (95 % CI +3.34, +11.96 %). Based on NORDCAN data, there was a statistically significant increase in the incidence of thyroid cancer in the Nordic countries during the same time period. In both women and men a joinpoint was detected in 2006. The incidence increased during 2006-2013 in women; APC +6.16 % (95 % CI +3.94, +8.42 %) and in men; APC +6.84 % (95 % CI +3.69, +10.08 %), thus showing similar results as the Swedish Cancer Register. Analyses based on data from the Cancer Register showed that the increasing trend in Sweden was mainly caused by thyroid cancer of the papillary type.
CONCLUSIONS: We postulate that the whole increase cannot be attributed to better diagnostic procedures. Increasing exposure to ionizing radiation, e.g. medical computed tomography (CT) scans, and to RF-EMF (non-ionizing radiation) should be further studied. The design of our study does not permit conclusions regarding causality.
AUTHORS' ABSTRACT: Hardell et al. 2016 (IEEE #6448): The Stockholm Central Railway Station in Sweden was investigated for public radiofrequency (RF) radiation exposure. The exposimeter EME Spy 200 was used to collect
the RF exposure data across the railway station. The exposimeter covers 20 different radiofrequency bands from 88 to 5,850 MHz. In total 1,669 data points were recorded. The median value for total exposure was 921 ¼W/m2 (or
0.092 ¼W/cm2; 1 ¼W/m2=0.0001 ¼W/cm2) with some outliers over 95,544 ¼W/m2 (6 V/m, upper detection limit). The mean total RF radiation level varied between 2,817 to 4,891 ¼W/m2 for
each walking round. High mean measurements were obtained for GSM + UMTS 900 downlink varying between 1,165 and 2,075 ¼W/m2. High levels were also obtained for UMTS 2100 downlink; 442 to 1,632 ¼W/m2. Also LTE 800 downlink, GSM 1800 downlink, and LTE 2600 downlink were in the
higher range of measurements. Hot spots were identified, for example close to a wall mounted base station yielding over 95,544 ¼W/m2 and thus exceeding the exposimeter's detection
limit. Almost all of the total measured levels were above the precautionary target level of 3-6 ¼W/m2 as proposed by the BioInitiative Working Group in 2012. That target level was one-tenth of the scientific benchmark providing a safety margin
either for children, or chronic exposure conditions. We compare the levels of RF radiation exposures identified in the present study to published scientific results reporting adverse biological effects and health harm at levels equivalent to, or below those measured in this Stockholm Central Railway Station project.
It should be noted that these RF radiation levels give transient exposure, since people are generally passing through the areas tested, except for subsets of people who are there for hours each day of work.
AUTHORS' ABSTRACT: Carlberg and Hardell 2017 (IEEE #6756): Objective. Bradford Hills viewpoints from 1965 on association or causation were used on glioma risk and use of mobile or cordless phones.
Methods. All nine viewpointswere evaluated based on epidemiology and laboratory studies. Results. Strength:meta-analysis of case-control studies gave odds ratio (OR) = 1.90, 95% confidence interval (CI) = 1.312.76 with highest cumulative exposure. Consistency: the risk increased with latency, meta-analysis gave in the 10+ years latency group OR = 1.62, 95% CI = 1.202.19.
Specificity: increased risk for glioma was in the temporal lobe.Using meningioma cases as comparison group still increased the risk.
Temporality: highest risk was in the 20+ years latency group,OR = 2.01, 95% CI =1.412.88, for wireless phones. Biological gradient: cumulative use of wireless phones increased the risk. Plausibility: animal studies showed an increased incidence of glioma and malignant schwannoma in rats exposed to radiofrequency (RF) radiation.There is increased production of reactive oxygen species (ROS) from RF radiation. Coherence: there is a change in the natural history of glioma and increasing incidence. Experiment:
antioxidants reduced ROS production from RF radiation. Analogy: there is an increased risk in subjects exposed to extremely
low-frequency electromagnetic fields. Conclusion. RF radiation should be regarded as a human carcinogen causing glioma.
AUTHOR'S ABSTRACT: Hardell 2017 (IEEE #6768): In May 2011 the International Agency for Research on Cancer (IARC) evaluated cancer risks from radiofrequency (RF) radiation. Human epidemiological studies gave evidence of increased risk for glioma and acoustic neuroma.
RF radiation was classified as Group 2B, a possible human carcinogen. Further epidemiological, animal and mechanistic
studies have strengthened the association. In spite of this, in most countries little or nothing has been done to reduce exposure and educate people on health hazards from RF
radiation. On the contrary ambient levels have increased. In 2014 the WHO launched a draft of a Monograph on RF fields and health for public comments. It turned out that five of the six members of the Core Group in charge of the draft
are affiliated with International Commission on Non-Ionizing Radiation Protection (ICNIRP), an industry loyal NGO, and thus have a serious conflict of interest. Just as by ICNIRP,
evaluation of non-thermal biological effects from RF radiation are dismissed as scientific evidence of adverse health effects in the Monograph. This has provoked many comments sent to the WHO. However, at a meeting on March 3, 2017 at the WHO
Geneva office it was stated that the WHO has no intention to change the Core Group.
AUTHORS' ABSTRACT: Hardell et al. 2017 (IEEE #6770): Exposure to radiofrequency (RF) radiation was classified as a possible human carcinogen, Group 2B, by the International Agency for Research on Cancer at WHO in 2011. The exposure pattern is changing due to the rapid development of technology. Outdoor RF radiation level was measured during five tours in Stockholm Old Town in April, 2016 using the EME Spy 200 exposimeter with 20 predefined frequencies. The results were based on 10,437 samples in total. The mean level of the total RF radiation was 4,293 µW/m2 (0.4293 µW/cm2). The highest mean levels were obtained for global system for mobile communications (GSM) + universal mobile telecommunications system (UMTS) 900 downlink and long-term evolution (LTE) 2600 downlink (1,558 and 1,265 µW/m2, respectively). The town squares displayed highest total mean levels, with the example of Järntorget square with 24,277 µW/m2 (min 257, max 173,302 µW/m2). These results were in large contrast to areas with lowest total exposure, such as the Supreme Court, with a mean level of 404 µW/m2 (min 20.4, max 4,088 µW/m2). In addition, measurements in the streets surrounding the Royal Castle were lower than the total for the Old Town, with a mean of 756 µW/m2 (min 0.3, max 50,967 µW/m2). The BioInitiative 2012 Report defined the scientific benchmark for possible health risks as 30-60 µW/m2. Our results of outdoor RF radiation exposure at Stockholm Old Town are significantly above that level. The mean exposure level at Järntorget square was 405-fold higher than 60 µW/m2. Our results were below the reference level on 10,000,000 µW/m2 established by the International Commission on Non-Ionizing Radiation Protection (ICNIRP), which, however, are less credible, as they do not take non-thermal effects into consideration and are not based on sound scientific evaluation. Our highest measured mean level at Järntorget was 0.24% of the ICNIRP level. A number of studies have found adverse, non-thermal (no measurable temperature increase) health effects far below the ICNIRP guidelines.
AUTHORS' ABSTRACT: Hardell and Carlberg 2017 (IEEE #6856): We used the Swedish Inpatient Register (IPR) to analyze rates of brain tumors of unknown type (D43) during 1998-2015. Average Annual Percentage Change (AAPC) per 100,000 increased with +2.06%, 95% confidence interval (CI) +1.27, +2.86% in both genders combined. A joinpoint was found in 2007 with Annual Percentage Change (APC) 1998-2007 of +0.16%, 95% CI -0.94, +1.28%, and 2007-2015 of +4.24%, 95% CI +2.87, +5.63%. Highest AAPC was found in the age group 20-39 years. In the Swedish Cancer Register the age-standardized incidence rate per 100,000 increased for brain tumors, ICD-code 193.0, during 1998-2015 with AAPC in men +0.49%, 95% CI +0.05, +0.94%, and in women +0.33%, 95% CI -0.29, +0.45%. The cases with brain tumor of unknown type lack morphological examination. Brain tumor diagnosis was based on cytology/histopathology in 83% for men and in 87% for women in 1980. This frequency increased to 90% in men and 88% in women in 2015. During the same time period CT and MRI imaging techniques were introduced and morphology is not always necessary for diagnosis. If all brain tumors based on clinical diagnosis with CT or MRI had been reported to the Cancer Register the frequency of diagnoses based on cytology/histology would have decreased in the register. The results indicate underreporting of brain tumor cases to the Cancer Register. The real incidence would be higher. Thus, incidence trends based on the Cancer Register should be used with caution. Use of wireless phones should be considered in relation to the change of incidence rates.
AUTHORS' ABSTRACT: Hedendahl, Hardell et al. 2017 (IEEE #6900). Introduction: Wireless access to the Internet is now commonly used in schools. Many schools give each student their own laptop and utilize the laptops and wireless fidelity (Wi-Fi) connection for educational purposes. Most children also bring their own mobile phones to school. Since children are obliged by law to attend school, a safe environment is important. Lately, it has been discussed if radiofrequency (RF) radiation can have long-term adverse effects on childrens health.
Method: This study conducted exposimetric measurements in schools to assess
RF emissions in the classroom by measuring the teachers RF exposure in order to
approximate the childrens exposure. Teachers in grades 712 carried a body-borne
exposimeter, EME-Spy 200, in school during 14 days of work. The exposimeter can
measure 20 different frequency bands from 87 to 5,850 MHz.
Results: Eighteen teachers from seven schools participated. The mean exposure to
RF radiation ranged from 1.1 to 66.1 ¼W/m2. The highest mean level, 396.6 ¼W/m2,
occurred during 5 min of a lesson when the teacher let the students stream and watch
YouTube videos. Maximum peaks went up to 82,857 ¼W/m2 from mobile phone uplink.
Discussion: Our measurements are in line with recent exposure studies in schools in
other countries. The exposure levels varied between the different Wi-Fi systems, and if
the students were allowed to use their own smartphones on the schools Wi-Fi network
or if they were connected to GSM/3G/4G base stations outside the school. An access
point over the teachers head gave higher exposure compared with a school with a
wired Internet connection for the teacher in the classroom. All values were far below
International Commission on Non-Ionizing Radiation Protections reference values, but
most mean levels measured were above the precautionary target level of 36 ¼W/m2
as proposed by the Bioinitiative Report. The length of time wireless devices are used is
an essential determinant in overall exposure. Measures to minimize childrens exposure
to RF radiation in school would include preferring wired connections, allowing laptops,
tablets and mobile phones only in flight mode and deactivating Wi-Fi access points, when not used for learning purposes.