Modification of cancer risk in offspring by parental cancer (Sweden)

Objectives: Familial cancer risks were studied in offspring whose parents h ad a similar (concordant) or a different (discordant) cancer in order to as sess the modification of cancer risks from one generation to another. Methods: We used the nation-wide Swedish Family-Cancer Database to calculat e familial rate ratios (FRRs) to the offspring when their parents had conco rdant and discordant cancers. Cancer sites were included if there was at le ast one pair of parents with the same cancer. In situ cancers were included in a separate analysis in order to increase the numbers of cases. Results: The risk of colon, all bowel, lung and breast cancer and melanoma increased 1.1-1.2 times when one parent and 1.3-1.6 times when two parents had any discordant cancer, suggesting involvement of environmental and here ditary effects shared by many forms of cancer. When both parents had colon cancer or melanoma, the respective risks in the offspring were 3.0 and 9.3 but only based on single triplets. For all bowel cancer the risk was 3.4, a pproximately multiplicative from the familial one parent-offspring risk. Fo r concordant lung and breast cancer triplets the risk in offspring was 11.8 and 29.4, respectively. Conclusions. Even discordant cancer in parents increased cancer risk in off spring. This may be due to environmental and hereditary causes, and deserve s consideration in epidemiological studies. The high risks in families wher e both parents had the same cancer suggest interactions of hereditary and e nvironmental factors.