Fig 2.

Familial risk of common cancers. Most common cancers, including breast, colorectal, and prostate cancer, exhibit familial aggregation, with the disease being more common in family members than in the general population. While familial aggregation may be secondary to genetic or environmental factors, evidence from monozygotic twins of patients suggests that genetic factors are mainly responsible.^11,12 As demonstrated in this figure, known high-penetrance cancer predisposition syndromes explain only a fraction of the familial risk of cancer.^13–16 While genome-wide association studies have identified numerous low-penetrance loci for each of these three common cancers, their contribution to the familial risk of cancer remains limited and a large portion of the familial risk of these cancers remains unexplained. GWAS, genome-wide association study; SNP, single nucleotide polymorphisms.