Familial cancers in a nationwide family cancer database: age distribution and prevalence.

We calculated sex- and age-specific familial relative risks (FRRs) of cancer in offspring of cancer probands at 19 male and 20 female cancer sites, based on the nationwide Family Cancer Database from Sweden. The proportion of familial cancers among all cancers was also determined. The database contained 550,000 primary cancers. The familial risk at known sites: colon, breast, ovary, testis, skin (melanoma), nervous system, thyroid and other endocrine glands were confirmed. The FRR of thyroid cancer exceeded any other cancer and was over twice as high for male as for female offspring, and appeared to constitute an early- and late-onset component. Novel register-based findings were familial risks in cervical and uterine cancer, and in male offspring of male probands kidney and skin (mainly squamous cell) cancer. Familial risks were noted also for lung cancer, lymphoma and leukaemia but they may have largely environmental causes. The proportion of familial cancers depended on the site, ranging from 11% in prostate to 8.7% in female breast and to well below 1% at many sites.