It is well-known that prostate cancer often "runs in families." Men with close relatives (especially their fathers or brothers) who have had prostate cancer have a much higher risk of developing it themselves.
It is likely that two components that contribute to the increased risk of prostate cancer among men who have family members with prostate cancer:
Family Health Habits
Men who grow up in the same family often develop the same health habits.
They tend to eat similar diets, exercise in similar amounts, have similar weight problems, etc. Daily lifestyle habits have been shown to have some effect on the overall risk of developing any number of medical conditions including prostate cancer.
Lifestyle choices and familial health habits are definitely not the whole story when it comes to prostate cancer in families, however.
Genetics
The increased risk of prostate cancer among male family members persists when those men have vastly different lifestyles, live in completely different environments, or even have never met (in the case of children who were put up for adoption).
This means that there must be a genetic component to the increased risk among family members.
Scientists have learned a great deal recently about the possible genetic basis for prostate cancer in some men. Many researchers believe that genetics plays a dominant role in whether or not some men get prostate cancer and plays little to no role for other men.
A great deal more discovery is needed in order to fully understand the role of genetics on prostate cancer risk.
The Bottom Line
The fact that prostate cancer runs in families is due to both genetics as well as health habits that are passed down through families.
Sources:
Carter BS, Bova GS, Beaty TH, et al.: Hereditary prostate cancer: epidemiologic and clinical features. J Urol 150 (3): 797-802, 1993.
Page WF, Braun MM, Partin AW, et al.: Heredity and prostate cancer: a study of World War II veteran twins. Prostate 33 (4): 240-5, 1997.
Verhage BA, Baffoe-Bonnie AB, Baglietto L, et al.: Autosomal dominant inheritance of prostate cancer: a confirmatory study. Urology 57 (1): 97-101, 2001.
