The risk that a common cancer

The risk that a common cancer will occur in relatives of an
affected person is generally low, but familial aggregations that
cannot be explained by environmental factors alone exist for
some neoplasms. Up to 5% of cases of breast, ovary, and bowel
cancers are inherited because of mutations in incompletely
penetrant, autosomal dominant genes. There are also several
cancer predisposing syndromes that are inherited in a
mendelian fashion, and the genes responsible for many of
these have been cloned.