The risk of malignant tumours in first-degree relatives of men with early onset prostate cancer: a population-based cohort study.

Previous studies have indicated that hereditary prostate cancer is common among men with early onset prostate cancer. The aim of this study was to investigate the incidence of malignant tumours in first-degree relatives of men with early onset prostate cancer. All prostate cancer cases diagnosed before the age of 51 years from 1958 to 1994 were identified in the population-based Swedish Cancer Register. The first-degree relatives of clinical cases were identified through parish data. Their vital status and cancer incidence were studied in the Swedish Cancer Register, the Cause of Death Register and the Census Register. The expected incidence of malignant tumours for the first-degree relatives were calculated using regional cancer register data. Cause-specific standardised incidence ratios (SIR) and 95% confidence intervals (CI) were calculated. The study included 423 first-degree relatives of 89 men with clinical prostate cancer. The first-degree relatives' SIR for malignant tumours was 0.99 (95% CI 0.78-1.23). The SIR for prostate cancer diagnosed at any age was 1.43 (95% CI 0.82-2.33), and 3.37 for first-degree relatives diagnosed before the age of 70 years (95% CI 1.36-6.94). There was no significantly increased risk of any non-prostatic malignant tumour. Only in five of the families did the pedigree show a pattern of hereditary prostate cancer. The first-degree relatives of men with early onset prostate cancer had more than a 3-fold increase in the risk of developing prostate cancer before the age of 70 years, but their total cancer risk was not increased. This study does not support the assumption that dominantly inherited susceptibility is a major cause of early onset prostate cancer.