Cancer risks to spouses and offspring in the family-cancer database

It is generally accepted that cancer is caused by environmental and inherit ed factors but these are only partially identified. Family studies can be i nformative but they do not separate shared lifestyles and genes. We estimat e familial risks for concordant cancers between spouses in common cancers o f both sexes in order to quantify cancer risks from the shared environment. The risks are compared to those seen between parents and offspring in orde r to estimate the inherited component. The nation-wide Family-Cancer Databa se was used as the source of family and cancer data. Standardized incidence ratios (SIRs) were calculated for concordant cancer in offspring by parent al cancer and in spouses. Among the 23 cancer sites considered, all but two showed an increased SIR for off-spring by father or mother. Only two sites , stomach and lung, showed an increase in SIR of concordant cancer among sp ouses. Additionally, pancreatic cancer and melanoma were increased in coupl es where at least one spouse was diagnosed before age 50. If both spouses p resented melanoma before age 40, SIR was 3.82 for husbands. SIRs of colon, renal, and skin (squamous cell) cancers were unchanged by spouses' concorda nt cancer. Shared lifestyle among spouses seems to explain only a small pro portion of cancer susceptibility. Because lifestyles are likely to differ m ore between parents and offspring than between spouses, familial cancer ris ks between parents and offspring are likely to be more due to heritable rat her than environmental effects. (C) 2001 Wiley-Liss, Inc.