Familial risks by proband status and age are useful for clinical counseling, and they can be used to calculate population-attributable fractions (PAFs), which show the proportion of disease that could be prevented if the cause could be removed.
The authors used the nationwide Swedish Family-Cancer Database on 10.2 million individuals and 182,104 fathers and 3710 sons with medically verified prostate carcinoma to calculate age specific familial standardized incidence ratios (SIRs) with 95% confidence intervals (95%CI) and familial PAFs for prostate carcinoma in sons ages 0-66 years.
The incidence of prostate carcinoma was doubled between the years 1961 and 1998. The familial SIRs for prostate carcinoma were 2.38 (95%CI, 2.18-2.59) for men with prostate carcinoma in the father only, 3.75 (95%CI, 2.73-4.95) for men with prostate carcinoma in a brother only, and 9.44 (95%CI, 5.76-14.03) for men with prostate carcinoma in both a father and a brother. The corresponding familial PAFs were 8.86%, 1.78%, and 0.99%, respectively, yielding a total PAF of 11.63%. Age specific risks were shown for the same proband histories. The SIR was 8.05 for prostate carcinoma before age 55 if a brother had been diagnosed before that age. If, in addition, a father was diagnosed at any age, then the SIR was 33.09.
The authors recommend that having a brother who is diagnosed with prostate carcinoma before age 55 years or having a brother and father who are diagnosed at any age are indications to screen for prostate carcinoma. The familial PAF of prostate carcinoma among a population of sons ages 0-66 years was 11.63%.