As many as 9 percent of Caucasian males and 10 percent of African-American males in the US will develop prostate cancer in their lifetime.

The majority of cases of prostate cancer are sporadic, which means that one person in the family developed prostate cancer by chance at a typical age of onset. In these cases, other male relatives have little to no increased risk of developing prostate cancer.

About 15 percent of prostate cancers are familial, which means there is a father or brother also affected, at typical ages of onset. Familial cancers may be due to a combination of genes and shared lifestyle factors or environmental exposures (multifactorial inheritance). On the other hand, some of these histories can represent a chance occurrence of sporadic cancers. A familial history may also arise due to a single gene mutation (hereditary cancer) that has reduced penetrance (a mutation associated with lower cancer risks and later onset of cancer). In general, with familial cancer, close relatives have a modestly increased risk of developing the cancer in question. The chance that genetic testing will be beneficial in further assessing cancer risks is usually small. Studies have found a trend of an increased chance to develop prostate cancer, with an increasing number of family members. In other words, the more relatives you have with prostate cancer, the higher the risk:

Approximately 5 percent to 10 percent of all prostate cancers and 45 percent of cases in men younger than age 55 can be attributed to a cancer susceptibility gene that is inherited as a dominant trait (from parent to child). Genetic heterogeneity has been observed with prostate cancer, which means that more than one gene has been implicated in its cause, including genes on chromosomes #1, 7, 8, 10, 11, 17, and X. At present, there are many continuing research studies to determine the specific mechanism of how gene mutations contribute to an increased susceptibility for prostate cancer; clinical testing is not available at the time of this writing.