How common is familial cancer?

Background: Family history of a disease may point to its heritable or environmental etiology. It can be described by the proportion of the familial disease, i.e. same disease in two or more family members. A family history always needs to be specified as to the number of generations covered and their ages. Patients and methods: Proportions of site-specific familial cancers (familial proportions) were calculated using the Swedish Family-Cancer Database, the largest dataset of its kind in the world, with cancers from the Swedish Cancer Registry. Familial proportions refer to the offspring population up to age 72 years when their parents or siblings were diagnosed with a concordant (same) cancer. Results: A total of 34 cancer sites and 205 638 cases were covered. Prostate cancer showed the highest familial proportion of 20.15%, followed by breast (13.58%) and colorectal (12.80%) cancers. Salivary gland cancers showed the lowest familial proportion of 0.15%, but bone, laryngeal, anal, connective tissue and other genital cancers also remained <1%. The familial proportion depended on the prevalence of the particular cancer and on its familial risk. Conclusions: The derived familial proportions can justifiably be used in statements 'X% of the patients had a family history of the cancer'.