An overview of the conference on low level lead toxicity.

Some earlier studies based on relatively small data sets have suggested that the month of diagnosis affects survival of breast cancer patients. This phenomenon has been suggested to be attributable to daylight-related hormonal factors. Factors related to the holidays of both the medical personnel and the women themselves might also provide the explanation. In this study we assessed the effect of the month of diagnosis on the survival of 32,807 female breast cancer patients diagnosed in Finland in 1956-1985. Our results indicate that the month of diagnosis is a significant prognostic factor after adjusting for age at diagnosis, period of diagnosis, and stage at diagnosis. The adjusted relative excess risk of death was highest among those diagnosed in July and August, and lowest in March and November, the difference between the lowest and highest risk being 18%. Since colorectal cancer should not have any daylight-related hormone dependent risk determinants, a control cohort of 12,950 women with a diagnosis of colorectal cancer in the same calendar period was studied in a similar way. The survival pattern by month of diagnosis among the colorectal cancer patients was similar to that among breast cancer patients, indicating that general factors associated with the health behaviour of women and the health services (such as holidays) rather than biological factors may cause seasonal variations in survival of cancer patients. Seasonal variations in survival of breast cancer patients have been described in New Zealand (Mason et al., 1990) and Finland (Joensuu & Toikkanen, 1991). Differences in patient series, methods of data acquisition, and seasons in the opposite hemispheres make direct comparisons between these series difficult, but evidently the variations did not appear during the same seasons (Joensuu & Toikkanen, 1991). Some authors have found no seasonal variation in survival of breast cancer patients (Galea & Blamey, 1991). As a consequence of the results of a city-based study (Joensuu & Toikkanen, 1991), we decided to carry out a nationwide survival study of female patients with breast or colorectal cancer. The aim of the study was to establish whether there were indeed variations in survival of cancer patients depending on the month of diagnosis. Such variations might be explained by differences in patient delay and health services due to, e.g. summer holidays, or by differences in the biology of the host or the disease. The former theory would be supported, if women whose breast cancers were diagnosed in the …