1596
In the remote possibility of one of our divers having a symptomatic bubble embolus, hyperbaric treatment is immediately
available. The morbidity of contrast echocardiography is, as James points out, about 0-07% in 41000 studies, with no mortality (to our knowledge). This seems a safe test. We have had no side-effects with 60 studies. Exercise testing is a well-established investigation for ischaemic heart disease. It has a complication rate (mortality, myocardial infarction, serious arrhythmia) of 0-09% in 518 448 tests.2 Would James propose that clinicians abandon this more hazardous procedure? The paper James cites in respect of cerebral perfusion deficits in divers with DCS3 had no control non-divers: so it is difficult to say how many of the defects were due to DCS. The ocular fundus lesions described in divers4 are asymptomatic, and their relevance is not known. We think that contrast echocardiography is a safe procedure, relevant to both commercial and sports divers, and we see no reason to abandon it.
ISCO International Standardised Classification of Occupations
TABLE II OBSERVED (0) AND EXPECTED (E) NEW CASES OF MALE BREAST CANCER
STEPHEN J. CROSS LESLEY F. THOMSON HAI SHAING LEE THOMAS G. SHIELDS KEVIN P. JENNINGS
of
Department Cardiology, Royal Infirmary,
Aberdeen
Fosterhill, Aberdeen AB9 2ZD, UK and Hyperbaric Medicine Unit, Aberdeen
TABLE I-OCCUPATIONS WITH POTENTIAL EXPOSURE TO ELF FIELDS NORWEGIAN 1960 CENSUS, FOLLOW-UP 1961-85
Royal Infirmary
-
-
-
-
-
-
1. Lee
F, Ginzton L. A central nervous system complication of contrast echocardiography. J Clin Ultrasound 1983; 11: 292-94. 2. Stuart R, Ellastad MH. National survey of exercise stress testing facilities. Chest 1980; 77: 94-97. 3. Adkisson G, MacLeod M, Hodgson M, et al. Cerebral perfusion deficits in dysbaric illness. Lancet 1989; ii: 119-21. 4. Polkinghorne PJ, Sehmi K, Cross MR, et al. Ocular fundus lesions in divers. Lancet 1988; ii: 1381-83.
Electromagnetic fields and male breast cancer
SiR,—Several reports during the past decade have suggested an association between occupational exposure to very-low-frequency electric and/or magnetic (ELF) fields and cancer, especially leukaemia and brain cancer. 1,2 An association between female breast cancer and exposure to overhead power transmission lines was found in a Colorado case-control study of adult cancer.3 An increased risk of male breast cancer has also been reported in male workers exposed to ELF fields. 4.5The hypothesis that use of electric power may increase risk of breast cancer has been discussed by Stevens,6who evaluated the experimental and epidemiological studies. His hypothesis is based on experimental evidence that shows an effect of light and ELF fields on pineal melatonin production, and on the relation of melatonin to mammary
carcinogenesis. We have studied breast cancer risk in Norwegian males holding occupations associated with exposure to ELF fields, according to census data. The Cancer Registry of Norway has obtained from the Norwegian Central Bureau of Statistics data covering all living persons 20 years or older and alive at the 1960 census, including data on occupation. Data have been linked to the 1970 census and to the cancer registry by their identification number. From this file a cohort of 37 952 men in the 1960 census in an occupation with a potential exposure to ELF fields was selected (table I). Standardised incidence ratios (SIR) were calculated for male breast cancer with the incidence rates for all economically active men at the 1960 census as standard rates. During the 25 years of follow-up (1961-85), 12 cases were observed; 5.81 were expected (SIR 207,95% confidence interval [CI] 107-361). Table n shows the distribution of breast cancer among electrical workers according to occupational status at the 1960 and 1970 censuses and with different follow-up periods. The table also shows breast cancer incidence by occupational group for the follow-up 1961-85. The results indicate an association between these occupations and incidence of male breast cancer, but the numbers are small and
the results should be interpreted with caution. The distribution of breast cancer among the selected subgroups of this type of occupation also supports an association, although the job titles selected may not be the best for an evaluation of cancer risk to workers exposed to ELF fields. A rise in risk of male breast cancer among those with an occupation entailing ELF field exposure both in 1960 and in 1970 cannot be claimed. Register data does not allow for extended confounder analysis, because of lack of information on actual job exposures and other factors relevant for development of breast cancer. Our results seem to support the justification of further studies on the association between breast cancer and occupational exposure to ELF fields. Cancer Registry of Norway, 0310 Oslo 3, Norway
TORE TYNES AAGE ANDERSEN
1. Savitz
DA, Calle EE. Leukemia and occupational exposure to electromagnetic fields: epidemiologic surveys. J Occup Med 1987; 29: 47-51. 2. Modan B. Exposure to electromagnetic fields and brain malignancy: A newly discovered menace? Am J Ind Med 1988; 13: 625-27. 3. Wertheimer N, Leeper E. Adult cancer related to electric wires near home. Int J Epidemiol 1982; 11: 4; 345-55. 4. Matanoski GM, Breysse P. The Hopkins telephone worker study. Poster at Contractors Review Meeting (Portland, Oregon, Nov 13-16, 1989). 5. Deemers PA, et al. Occupational exposure to electromagnetic radiation and breast cancer in males. AmJ Epidemiol 1990; 132: 775-76. 6. Stevens R. Electric power use and breast cancer: a hypothesis. Am J Epidemiol 1987; review of
125: 556-61
CORRECTIONS Risk factors for transmission of hepatitis B virus to Gambian children In this article by Dr M. Vall Mayans and colleagues (Nov 3, p 1107), the acknowledgements should have stated that this work was partly supported by the Department of Cooperation and Development of the Ministry of Foreign Affairs of Italy.
Antibody profile of early HTLV-L infection. In this article by Dr Y-M. A. Chen and colleagues (Nov 17, p 1214) line 5 of the second paragraph of the Introduction should have read "from New York City, 7 were seronegative" and line 4 of the Subjects and methods "enrolled in the study (69% of the 2221 adults in the villages)."
In the remote possibility of one of our divers having a symptomatic bubble embolus, hyperbaric treatment is immediately
available. The morbidity of contrast echocardiography is, as James points out, about 0-07% in 41000 studies, with no mortality (to our knowledge). This seems a safe test. We have had no side-effects with 60 studies. Exercise testing is a well-established investigation for ischaemic heart disease. It has a complication rate (mortality, myocardial infarction, serious arrhythmia) of 0-09% in 518 448 tests.2 Would James propose that clinicians abandon this more hazardous procedure? The paper James cites in respect of cerebral perfusion deficits in divers with DCS3 had no control non-divers: so it is difficult to say how many of the defects were due to DCS. The ocular fundus lesions described in divers4 are asymptomatic, and their relevance is not known. We think that contrast echocardiography is a safe procedure, relevant to both commercial and sports divers, and we see no reason to abandon it.
ISCO International Standardised Classification of Occupations
TABLE II OBSERVED (0) AND EXPECTED (E) NEW CASES OF MALE BREAST CANCER
STEPHEN J. CROSS LESLEY F. THOMSON HAI SHAING LEE THOMAS G. SHIELDS KEVIN P. JENNINGS
of
Department Cardiology, Royal Infirmary,
Aberdeen
Fosterhill, Aberdeen AB9 2ZD, UK and Hyperbaric Medicine Unit, Aberdeen
TABLE I-OCCUPATIONS WITH POTENTIAL EXPOSURE TO ELF FIELDS NORWEGIAN 1960 CENSUS, FOLLOW-UP 1961-85
Royal Infirmary
-
-
-
-
-
-
1. Lee
F, Ginzton L. A central nervous system complication of contrast echocardiography. J Clin Ultrasound 1983; 11: 292-94. 2. Stuart R, Ellastad MH. National survey of exercise stress testing facilities. Chest 1980; 77: 94-97. 3. Adkisson G, MacLeod M, Hodgson M, et al. Cerebral perfusion deficits in dysbaric illness. Lancet 1989; ii: 119-21. 4. Polkinghorne PJ, Sehmi K, Cross MR, et al. Ocular fundus lesions in divers. Lancet 1988; ii: 1381-83.
Electromagnetic fields and male breast cancer
SiR,—Several reports during the past decade have suggested an association between occupational exposure to very-low-frequency electric and/or magnetic (ELF) fields and cancer, especially leukaemia and brain cancer. 1,2 An association between female breast cancer and exposure to overhead power transmission lines was found in a Colorado case-control study of adult cancer.3 An increased risk of male breast cancer has also been reported in male workers exposed to ELF fields. 4.5The hypothesis that use of electric power may increase risk of breast cancer has been discussed by Stevens,6who evaluated the experimental and epidemiological studies. His hypothesis is based on experimental evidence that shows an effect of light and ELF fields on pineal melatonin production, and on the relation of melatonin to mammary
carcinogenesis. We have studied breast cancer risk in Norwegian males holding occupations associated with exposure to ELF fields, according to census data. The Cancer Registry of Norway has obtained from the Norwegian Central Bureau of Statistics data covering all living persons 20 years or older and alive at the 1960 census, including data on occupation. Data have been linked to the 1970 census and to the cancer registry by their identification number. From this file a cohort of 37 952 men in the 1960 census in an occupation with a potential exposure to ELF fields was selected (table I). Standardised incidence ratios (SIR) were calculated for male breast cancer with the incidence rates for all economically active men at the 1960 census as standard rates. During the 25 years of follow-up (1961-85), 12 cases were observed; 5.81 were expected (SIR 207,95% confidence interval [CI] 107-361). Table n shows the distribution of breast cancer among electrical workers according to occupational status at the 1960 and 1970 censuses and with different follow-up periods. The table also shows breast cancer incidence by occupational group for the follow-up 1961-85. The results indicate an association between these occupations and incidence of male breast cancer, but the numbers are small and
the results should be interpreted with caution. The distribution of breast cancer among the selected subgroups of this type of occupation also supports an association, although the job titles selected may not be the best for an evaluation of cancer risk to workers exposed to ELF fields. A rise in risk of male breast cancer among those with an occupation entailing ELF field exposure both in 1960 and in 1970 cannot be claimed. Register data does not allow for extended confounder analysis, because of lack of information on actual job exposures and other factors relevant for development of breast cancer. Our results seem to support the justification of further studies on the association between breast cancer and occupational exposure to ELF fields. Cancer Registry of Norway, 0310 Oslo 3, Norway
TORE TYNES AAGE ANDERSEN
1. Savitz
DA, Calle EE. Leukemia and occupational exposure to electromagnetic fields: epidemiologic surveys. J Occup Med 1987; 29: 47-51. 2. Modan B. Exposure to electromagnetic fields and brain malignancy: A newly discovered menace? Am J Ind Med 1988; 13: 625-27. 3. Wertheimer N, Leeper E. Adult cancer related to electric wires near home. Int J Epidemiol 1982; 11: 4; 345-55. 4. Matanoski GM, Breysse P. The Hopkins telephone worker study. Poster at Contractors Review Meeting (Portland, Oregon, Nov 13-16, 1989). 5. Deemers PA, et al. Occupational exposure to electromagnetic radiation and breast cancer in males. AmJ Epidemiol 1990; 132: 775-76. 6. Stevens R. Electric power use and breast cancer: a hypothesis. Am J Epidemiol 1987; review of
125: 556-61
CORRECTIONS Risk factors for transmission of hepatitis B virus to Gambian children In this article by Dr M. Vall Mayans and colleagues (Nov 3, p 1107), the acknowledgements should have stated that this work was partly supported by the Department of Cooperation and Development of the Ministry of Foreign Affairs of Italy.
Antibody profile of early HTLV-L infection. In this article by Dr Y-M. A. Chen and colleagues (Nov 17, p 1214) line 5 of the second paragraph of the Introduction should have read "from New York City, 7 were seronegative" and line 4 of the Subjects and methods "enrolled in the study (69% of the 2221 adults in the villages)."
