Prostate cancer is a malignant (cancerous) tumor that begins in a man's prostate gland. The prostate gland is the size and shape of a walnut and located behind the base of the penis, in front of the rectum, and below the bladder. Prostate cancer has been the source of enormous public and professional interest over the last few years, and the recent introduction of PSA screening and changes in disease management have led to changes in incidence trends and treatment. Prostate cancer is classified as a malignant tumor because it is a mass of cells which can invade other parts of the body, where this invasion of other organs is called metastasis.

Prostate cancer starts when normal cells in the gland undergo a change that leads to abnormal growth. It can grow unnoticed for years, with no obvious symptoms. Prostate cancer risk is much higher after the age of 50 years old, and African American men have the highest risk of prostate cancer. Treatment of Prostate cancer often depends on the stage of the cancer. Depending how fast the cancer grows and how different it is from surrounding tissue helps determine the stage it is in.

Prostate cancer commonly is treated with radiation therapy, which use high energy rays (similar to x-rays) to kill cancer cells. Prostate cancer affects one in six men and is known as the second leading cause of cancer death among men in the US. Gene therapy shows promise as a treatment strategy that can help target both localized and metastatic types of prostate cancer.

Radiation may cause damage to these normal tissues leading to side effects such as temporary or occasionally permanent urinary, gastrointestinal, or sexual dysfunction. Radiation therapy is sometimes used after surgery or instead of surgery, where this treatment is aimed directly at the tumor to kill the cancer cells. Radiation therapy is most often recommended to patients whose cancer has not spread outside the prostate, and the treatment's effectiveness at curing the disease is similar to surgery.