Family history and prostate cancer risk in a population-based cohort of Iowa men

A family history of prostate cancer has been associated with prostate cance r risk in most prior studies, and more limited data suggest that a family h istory of breast cancer may also be important; however, there are no data f rom a population-based cohort study of prostate cancer incidence that adjus ts for major confounders. We conducted follow-up through 1995 on 1557 men, ages 40-86 years, who were randomly selected (81% response rate) as cancer- free controls for a population-based case-control study conducted in Iowa f rom 1987-1989, Family history of cancer in parents and siblings was obtaine d using a mailed questionnaire. Incident cancers and deaths were ascertaine d through linkages to state and national databases; 101 incident cases of p rostate cancer were identified, At baseline, 4.6% of the cohort reported a family history of prostate cancer in a brother or father, and this was posi tively associated,vith prostate cancer risk after adjustment for age [relat ive risk (RR) = 3.2; 95% confidence interval (CI), 1.8-5.7] or after multiv ariate adjustment for age, alcohol, and dietary factors (RR = 3.7; 95% CI, 1.9-7.2). Risk was greater if a brother had prostate cancer (RR = 4.5; 95% CI, 2.1-9.7) than if a father had prostate cancer (RR = 2.3; 95% CI, 1.0-5. 3), Also at baseline, 9.6% of the cohort had a family history of breast and /or ovarian cancer in a mother or sister, and this was positively associate d with prostate cancer risk (age-adjusted RR = 1.7; 95% CI, 1.0-3.0; multiv ariate RR = 1.7; 95% CI, 0.9-3.2). Men with a family history of both prosta te and breast/ovarian cancer were also at increased risk of prostate cancer (RR = 5.8; 95% CI, 2.4-14), There was no association with a family history of colon cancer. Exclusion of well-differentiated, localized tumors did no t alter these findings. These data from an incidence study confirm that a f amily history of prostate cancer is a strong prostate cancer risk factor af ter adjustment for dietary and other risk factors, and suggest that selecti on and recall bias have not had an important influence on most case-control study results. These data also support the idea that a family history of b reast cancer may also be a prostate cancer risk factor.