INCIDENCE OF BREAST-CANCER IN NORWEGIAN FEMALE RADIO AND TELEGRAPH OPERATORS

Exposure to electromagnetic fields may cause breast cancer in women if it increases susceptibility to sex-hormone-related cancer by diminish ing the pineal gland's production of melatonin. We have studied breast cancer incidence in female radio and telegraph operators with potenti al exposure to light at night, radio frequency(405 kHz-25 MHz), and, t o some extent, extremely low frequency fields (50 Hz). We linked the N orwegian Telecom cohort of female radio and telegraph operators workin g at sea to the Cancer Registry of Norway to study incident cases of b reast cancer. The cohort consisted of 2,619 women who were certified t o work as radio and telegraph operators between 1920 and 1980. Cancer incidence was analyzed on the basis of the standardized incidence rati o (SIR), with the Norwegian female population as the comparison group. The incidence of all cancers was close to unity (SIR = 1.2). An exces s risk was seen for breast cancer (SIR = 1.5), Analysis of a nested ca se-control study within the cohort showed an association between breas t cancer in women aged 50 + years and shift work. In a model with adju stment for age, calendar year, and year of first birth, the rate ratio for breast cancer associated with being a radio and telegraph operato r - in comparison with all Norwegian women born 1935 or later - analyz ed with Poisson regression,was 1.5 after adjustment for fertility fact ors, These results support a possible association between work as a ra dio and telegraph operator and breast cancer. Future epidemiologic stu dies on breast cancer in women aged 50 and over, should address possib le disturbances of chronobiological parameters by environmental factor s.