Some data suggest that brothers of prostate cancer patients have higher disease risk than their fathers, supporting an X-linked or recessive mode of inheritance. However, higher observed frequencies in brothers than fathers may merely reflect the strong temporal changes in US incidence rates.
Objectives: (a) to evaluate the fit of X-linked, recessive, and dominant modes of inheritance to prostate cancer incidence, specific for calendar year, age, and race, in population-based samples of US and Canadian families; and (b) to evaluate a simple multifactorial model for familial aggregation of prostate cancer due to shared low-penetrance variants of many genes or shared lifestyle factors.
Methods: The data consist of reported prostate cancer incidence in first-degree relatives of 1,719 white, African-American, and Asian-American men with and without prostate cancer at ages <70 years. Model parameters were estimated by maximizing a pseudo-likelihood function of the data, and goodness of model fit was assessed by evaluating discrepancies between observed and expected numbers of pairs of relatives with prostate cancer.
Results: After adjusting for temporal trends in prostate cancer incidence rates we found that the X-linked model fit poorly. underpredicting the observed number of affected father-son pairs. This also was true of the recessive model, although the evidence for poor fit did not achieve statistical significance. In contrast, the dominant model provided adequate fit to the data. In this model the race-specific penetrance estimates for carriers of deleterious genotypes were similar among African-Americans and whites, but lower among Asian-Americans: risk by age 80 years for carriers born in 1900 was estimated as 75.3% for African-Americans and whites, and 44.4% for Asian-Americans. None of the Mendelian models fit the data better than did the simple multifactorial model.
Conclusions: The good fit of the multifactorial model suggests that multiple genes, each having low penetrance, may be responsible for most inherited prostate cancer susceptibility, and that the contribution of rare highly penetrant mutations is small.