Heterogeneity in genetic susceptibility to prostate cancer

The incidence of prostate cancer is related to aging. Its increase in the last 10 years, varies from country to country and according to ethnic group, with its greatest incidence among African-American males and the least among Asian males. Only two risk factors have thus far been clearly established for prostate cancer: familial aggregation and ethnic origin. No dietary or environmental cause has yet been identified for prostate cancer. However, some variations in endogenous factors, such as sex steroids or IGF1 circulating levels, may partly explain differences in risk observed between different populations. Genetic polymorphisms of genes encoding for 5alpha-reductase, androgen receptor, or vitamin D receptor have been associated with different degrees of risk for prostate cancer and may explain variations in risk among ethnic groups or within geographic areas. Different studies support the theory that familial prostate cancer may be hereditary and not due to a similar lifestyle. Thus, familial inheritance is a parameter that must be considered when advising screening in high-risk families. Indeed, the relative risk for first-degree relatives of prostate cancer patients can reach 2, 5 and 11 when, respectively, 1, 2 and 3 first-degree relatives are affected. Some familial forms appear to be associated with transmission of a rare, putative, autosomal dominant gene (0.003-0.06 allele frequency) with a high penetrance (88% at age 85). Using this transmission model and linkage analysis, three predisposing loci on chromosome 1: HPC-1 (hereditary prostate cancer 1: 1q24-25), PCaP (predisposing for prostate cancer: 1q42-43) and CAPB (predisposing for prostate and brain tumor: 1p36) and one locus on chromosome 20 (HPC20: 20q13) have been described. Moreover, X-linked transmission has been suggested and related to another predisposing gene locus: HPCX (Xq27-28). It is possible that a large proportion of familial prostate cancer is due not to segregation of a few major gene mutations transmitted according to a monogenic inheritance, but rather to familial sharing of alleles at many loci, each contributing to a small increase in cancer risk.