Cancer risk in a cohort of Danes working in Greenland

Greenland is a high-incidence area for certain virus-associated cancers. The long term cancer risk in a cohort of 7,761 Danish employees who had been working for some time (median 19.7 months) in Greenland during the period 1955-1978 was studied. During a total of 162,300 person-years (average 20.9 years) of follow-up ending on December 31, 1992, the number of cancers observed was 732 vs. 669 expected (relative risk (RR) = 1.09, 95% confidence interval (CI) 1.02-1.18). Whereas the men did not experience any unusual cancer incidence at any cancer site, the women were at elevated risk of developing breast cancer (RR = 1.5, 95% CI 1.2-1.8 (n = 96)); malignant melanoma (RR = 1.8, 95% CI 1.0-2.9 (n = 16)); and lymphatic and hematopoietic malignancies (RR = 1.7, 95% CI 1.0-2.8 (n = 16)). Exposure during adulthood to a high-incidence area for cervical cancer, nasopharyngeal carcinoma and tumors of the major salivary glands did not confer any measurable increase in the risk for these virus-associated cancers. Postponement of childbearing might explain part of the elevated breast cancer risk. Intensive exposure to ultraviolet light, that is likely to explain the increased risk of malignant melanoma among the women, might also be involved in the excess incidence of lymphatic and hematopoietic malignancies observed in these women. However, why the men did not experience similar alterations in the risk of melanoma and cancers of the immune system is enigmatic.