Follow-up of radio and telegraph operators with exposure to electromagnetic fields and risk of breast cancer

It is still unclear whether exposure to electromagnetic fields (EMF) is associated with breast cancer. To further investigate the issue, we followed-up a cohort of Norwegian female radio and telegraph operators in the period 1 January 1961 to 31 May 2002, with 99 breast cancer cases. The standardized incidence ratio (SIR) for breast cancer was 1.30 (95% confidence intervals (CI) 1.05-1.58), compared with the total Norwegian female population. In a subsequent nested case-control study, exposure to radio frequency (405 kHz-25 MHz) and extremely low-frequency (50 Hz) fields due to stay in the radio room during day and night was cumulated by years of employment and workload according to ship type. The exposure was assessed in two age groups (<50, 50+) with regard to risk of breast cancer. The odds ratios in the group with the highest cumulative exposure were 1.78 (95% CI 0.59-5.41) and 2.37 (95% CI 0.88-6.36) in the younger and the older women, respectively. P-value for trend was 0.03 in both age groups. The results of the oestrogen receptor status analysis by exposure to EMF showed an increased risk of oestrogen receptor-positive breast cancer in the younger women, while the older age group had an elevated risk of oestrogen receptor-negative breast cancer. Thus, the present study contributes to the hypothesis of an association between occupational exposure to EMF and increased risk of breast cancer.

Risk of breast cancer among Norwegian women with visual impairment

Experimental studies suggest that melatonin has a protective effect against breast cancer. Exposure to light suppresses melatonin secretion, but to a lesser degree in totally blind persons. Breast cancer was investigated in a cohort of 15 412 Norwegian visually impaired women. The risk among totally blind women was 0.64 (95% CI = 0.21-1.49, 5 cases only), and for those who became blind before age of 65, the SIR was 0.51 (95% CI = 0.11-1.49). Our findings give support to the 'melatonin hypothesis'.

Incidence of breast cancer in a Norwegian cohort of women with potential workplace exposure to 50 Hz magnetic fields

BACKGROUND

The risk of breast cancer was investigated in a large dynamic population-based cohort of all 1.1 million economically active women in Norway with potential exposure to 50 Hz magnetic fields at the censuses of 1960, 1970, and 1980.

METHODS

The follow-up period for the cohort was 1961-1992. For each woman, date of birth and census information on occupation and socioeconomic status were ascertained. These data were linked to the breast cancer morbidity information in the Cancer Registry of Norway. Exposure to magnetic fields was assessed a priori using two different approaches. In the first approach, hours per week in a potential magnetic field above background level (0.1 microT) were classified by an expert panel. In the second approach, measured magnetic fields from a separate study of men at work were allocated to the women's census job titles. In both approaches, exposure was cumulated over the years of employment (work hours and microT-years, respectively).

RESULTS

The Poisson regression analysis showed a risk ratio (RR) of 1.14 (95% confidence interval (CI) = 1.10-1.19) in the highest exposure category compared to the lowest when using the first approach, and the corresponding RR was 1.08 (95% CI = 1.01-1.16) when using the second approach. For women younger than 50 years, RR was 1.20 (95% CI = 1.11-1.29) and 1.12 (95% CI = 0.98-1.28), respectively.

CONCLUSIONS

The results give some support to the hypothesis that exposure to 50 Hz magnetic fields may increase the risk of breast cancer. However, since no direct information on exposure was available, no firm conclusions can be drawn.

Survival of breast cancer patients in Lithuania and Norway, 1988-1992

In Norway, the incidence of breast cancer is almost twice that in Lithuania, whereas the mortality rates of the disease are approximately the same in both countries. The aim of the present study was to compare the survival of breast cancer patients in the two countries according to stage. The material from both countries included cases diagnosed between 1988 and 1992 with complete follow-up of date of death to the end of 1995. The Norwegian data consisted of all 9403 new cases recorded by the Norwegian Cancer Registry. The Lithuanian data included in all 1649 new cases treated at the Oncology Centre in Vilnius, which represents 40% of breast cancer cases in Lithuania--these cases had the same distribution of the disease by age and stage as for the whole country. The overall 5-year relative survival was lower in Lithuania (57.3%) than in Norway (78.4%). Lower survival was observed in Lithuania compared with Norway for all stages. In stage I, the difference was 7.8% in absolute terms which could be explained by a higher proportion of small tumours among the Norwegian cancer cases (63.7% of tumours were 2 cm or less, while in Lithuania the proportion of small stage I tumours was only 27.9%). Therefore, early diagnosis within the stage I category seems relevant. The difference in survival was, however, most pronounced in stage II (20%) and III (29%). In Norway, the better overall survival is partly explained by a more favourable stage distribution. The lower survival of Lithuanian cases within stage categories could be explained by more advanced metastases to regional lymph nodes and by higher proportions of large tumours within stage.