Familial prostate cancer and possible associated malignancies: nation-wide register cohort study in Sweden.

There is a familial aggregation of prostate cancer, and 5 to 10% of all prostate cancers are estimated to be inherited in an autosomal-dominant mode. A population-based cohort study was performed in order to study familial prostate cancer and associated malignancies. A nation-wide register cohort study was conducted using an unselected study population. The cohort of 5,595 sons and 5,089 daughters of Swedish men found to have prostate cancer between 1959 and 1963 was identified. All types of cancer reported between 1958 and 1992 in this cohort were identified through linkage to the Swedish Cancer Registry. The expected number of different cancers was calculated using incidence rates obtained from the Registry. A highly significant increased overall standardized incidence ratio (SIR) of 1.65 (95% CI, 1.49-1.83) was obtained for prostate cancer, with 370 observed cases compared with 224 expected prostate cancers. The SIR was 3.18 among cases 45 to 49 years old at diagnosis, with the risk gradually decreasing to a SIR of 1.45 among cases over 80 years of age. Among sons and daughters with a father whose prostate cancer was diagnosed at an early age (<70 years), an increased risk for colorectal cancer SIR 1.48 (1.10-1.95) was observed. No significant difference in cancer risk for other sites was observed among the daughters and sons of men with prostate cancer. This cohort study confirms earlier studies that a positive family history of prostate cancer is an important risk factor for developing this disease. Though increased risk was found for all ages, it was more pronounced in younger men. Since no other malignancy was significantly associated with prostate cancer, it is most likely that familial prostate cancer is "site-specific".