Relatives of prostate cancer patients have an increased risk of prostate and stomach cancers: a population-based, cancer registry study in Finland

Objective: Five to ten percent of prostate cancers may be caused by inherit ed genetic defects. In order to explore the nature of inherited cancer risk s in the genetically homogeneous Finnish population, we investigated the in cidence of prostate cancer and other cancers in first-degree relatives of p rostate cancer patients by linking the population-based parish records on r elatives with the Finnish Cancer Registry (FCR) data. Methods: The study population was composed of first-degree relatives of two groups of prostate cancer patients diagnosed in Finland during 1988-1993: (1) all early-onset (less than or equal to 60years) patients (n=557) from t he entire country, (2) a sample (n=989) of prostate cancer patients diagnos ed at an age of > 60 years. A total of 11,427 first-degree relatives were i dentified through parish records, and their cancer incidence was determined based on a total of 299,970 person-years. Standardized incidence ratios (S IR) were calculated based on expected cancer rates in the general populatio n. Results: The SIR of prostate cancer was increased in both Cohort 1 (2.5, 95 % CI 1.9-3.2) and Cohort 2 (1.7, 95% CI 1.4-2.1). The risk of prostate canc er was high for relatives of patients diagnosed at an early age, and then l eveled off for patients in the median age of prostate cancer diagnosis (70- 79 years). However, the prostate cancer risk for relatives of patients diag nosed greater than or equal to 80years was again statistically significantl y elevated (SIR 1.8, 95% CI 1.3-2.6), suggesting a contribution of genetic factors to prostate cancer also at a late age of onset. Gastric cancer was the only other cancer type with a significantly elevated risk among the rel atives. Increased risk of gastric cancer was seen only in male relatives of prostate cancer patients diagnosed at an early age, with the highest risk detected for the male relatives of prostate cancer patients diagnosed at an age of 55 years or less (SIR 5.0, 95% CI 2.8-8.2). Conclusions: Our population-based study indicates that hereditary factors m ay play an important role in the development of prostate cancer among the r elatives of men diagnosed both at younger and older ages. This finding is r elevant in the context of our observations that HPCX (hereditary prostate c ancer susceptibility locus on Xq27-28) linkage in Finland is found exclusiv ely among families with late age of onset. The association of gastric cance r with prostate cancer has not been reported previously, and may reflect th e effects of a novel predisposition locus, which increases the risk to both of these common tumor types.