Early onset and familial predisposition to prostate cancer significantly enhance the probability for breast cancer in first degree relatives.

Genetic predisposition accounts for >/=10% of all cancer of the prostate (CaP) and is therefore considered a major risk factor, together with age and ethnic origin. Several epidemiological studies have suggested that familial clustering of CaP may be associated with an increased frequency of breast and other cancers among relatives. In order to correlate the incidence of CaP with prevalence of breast and other cancers, we have performed uni- and multi-variate analyses on 691 complete pedigrees including probands, who were consecutive patients with confirmed CaP treated in three French urological departments. We have shown a significantly higher risk (RR = 2.3, p = 0.01) to develop breast cancer in families with multiple than in those with a single CaP. Risk of observing other types of cancer within these families was not significant. We then calculated the breast cancer risk in early onset prostate cancer families, and observed a relative risk that is even more significant (RR = 5.5, p = 0.002). Furthermore, the risk was >30 times that a proband's mother have breast cancer if CaP occurred below 55 years of age, rather than after 75 years (p = 0.003). This study has therefore shown for the first time, the relatively high penetrance for breast cancer in relatives of early onset CaP patients. Copyright 2000 Wiley-Liss, Inc.