Prostate cancer is a malignant (cancerous) tumor (growth) that consists of cells from the prostate gland. Generally, the tumor usually grows slowly and remains confined to the gland for many years.
During this time, the tumor produces little or no symptoms or outward signs (abnormalities on physical examination). However, all prostate cancers do not behave similarly. Some aggressive types of prostate cancer grow and spread more rapidly than others and can cause a significant shortening of life expectancy in men affected by them. A measure of prostate cancer aggressiveness is the Gleason score (discussed in more detail later in this article), which is calculated by a trained pathologist observing prostate biopsy specimens under the microscope.
As the cancer advances, however, it can spread beyond the prostate into the surrounding tissues (local spread). Moreover, the cancer also can metastasize (spread even farther) throughout other areas of the body, such as the bones, lungs, and liver. Symptoms and signs, therefore, are more often associated with advanced prostate cancer.