Familial relationships in squamous cell carcinoma of the skin.

The Swedish Family-Cancer Database, which was updated in 1999 to cover individuals born after 1934 with their biological parents, totals 9.6 million persons. We used this resource to study invasive and in situ skin cancers. We identified 198 families in which a parent and an offspring had skin cancer. The familial standardized incidence ratios (SIRs) were 2.4 for invasive and 2.8 for in situ skin cancers in offspring. The SIRs for offspring depended only weakly on the age at diagnosis, as evaluated in two age groups. Compared with offspring whose parents had a single skin cancer, offspring whose parents had multiple skin cancers had a 70% increase in SIR. The discordant parental cancer sites that showed associations with skin cancer in offspring were melanoma, ocular melanoma, and a group of cancers observed in immunosuppressed patients.