Prostate cancer is the most common form of cancer, excluding skin cancer, in men in the United States. It is primarily diagnosed in men over 65, although it may begin much earlier. Some cancers of the prostate are very slow growing, while others behave aggressively. Prostate cancer often metastasizes to other tissue, including the brain, lungs, lymph nodes, and bones. Early detection is critical in order to increase the chances for survival. The cancer can be felt upon digital rectal examination (DRE). These examinations are recommended routinely for all men over the age of 50 and high-risk men should commence at age 40.

Little is known about the causes of prostate cancer. Risk factors for prostate cancer include family history and being African-American. While most prostate cancers are found in the peripheral zone, they may occur anywhere in the prostate. Most pathologists use the Gleason grading system to assess the tumor progression. A score from 2 to 4 indicates a well-differentiated cancer; 5 to 6 correlates with a moderately differentiated cancer; and 7 to 10 indicates a poorly differentiated cancer. The poorer the differentiation of the cancer cells (the higher the score), the worse the prognosis. Well-differentiated tumors grow slowly, whereas poorly differentiated tumors grow rapidly and are associated with a poor prognosis.