Carcinoma of the prostate is the most common malignancy in men in the West and, after lung cancer, the most common cause of cancer death in men over age 55. The incidence of prostate cancer increases dramatically with each decade after age 50, and disease rates appear to vary by population. North Americans (particularly African-Americans) develop prostate cancer at one of the highest rates in the world; Japan and Africa have low rates of the disease. These differences appear to be related to lifestyle: the children of Japanese immigrants to the U.S. develop prostate cancer at the same rate as their European American counterparts (84 cases per 100,000 after age 65).

Ninety-five percent of prostate cancers are adenocarcinomas. The other 5% include squamous cell carcinoma, transitional cell carcinoma, sarcoma and, rarely, metastatic disease from another primary site (lung, melanoma, or lymphoma). In the vast majority of cases, prostate cancer remains dormant for decades: one-third of malignancies are identified at autopsy.

No aetiological agent has been identified, but environmental, nutritional, hormonal, and genetic factors have been implicated. Because incidence increases among men who immigrate to the United States from areas with low incidence rates, a diet high in saturated fat may be a factor. In addition, workers in tyre and rubber manufacturing, sheet metal industries, farmers, and those exposed to cadmium have high mortality rates from prostate cancer. Some studies suggest that testosterone plays a role in the development of prostate cancer, but information is inconclusive. Family clusters have been identified, making hereditary risk likely.

Nonpalpable localised prostate cancer is often asymptomatic. Symptoms may be associated with local extension and distant metastases.