Familial prostate cancer in Sweden. A nationwide register cohort study.

BACKGROUND: Although prostate carcinoma is not widely recognized as a familial cancer, familial aggregation of this disease has been shown in some retrospective case-control studies. To study familial prostate cancer in Sweden, a population-based cohort study was performed, that attempted to avoid possible bias connected with some earlier studies of familial prostate cancer.
METHODS: A nationwide register cohort study was conducted using an unselected study population. The study cohort of 5496 sons of Swedish men found to have prostate cancer between 1959 and 1963 was identified through parish offices. All prostate cancer patients reported between 1958 and 1990 in this cohort were identified through linkage to the Swedish Cancer Register. The expected number of prostate cancer patients was calculated using incidence rates obtained from the same register.
RESULTS: A highly significant increased overall standardized incidence ratio (SIR) of 1.70 (95% confidence interval, 1.51-1.90) was obtained for prostate cancer in this cohort, with 302 observed cases compared with 178 expected prostate cancers. The SIR was 3.38 among patients aged 45-49 years at diagnosis, with the risk gradually decreasing to a SIR of 1.35 among patients older than 80 years (trend, P = 0.013). Among sons with a father whose prostate cancer was diagnosed at an early age (< 70 years), a significant trend (P = 0.01) for prostate cancer risk was observed due to early onset of the disease.
CONCLUSIONS: This cohort study provides further evidence that a positive family history of prostate cancer is a risk factor for developing the disease in an unselected population. The increased risk was found for all ages, but was more pronounced in younger men.