What is Prostate Cancer?

Prostate cancer is when cancer forms in the prostate gland. It is the second-leading cause of cancer deaths for men in the U.S. About 1 in 9 men will be diagnosed with prostate cancer in their lifetime. This year, nearly 165,000 men will be diagnosed with prostate cancer.

Growths in the prostate can be benign (not cancer) or malignant (cancer).

Benign growths (like benign prostatic hypertrophy (BPH):

  • Are rarely a threat to life
  • Don't invade the tissues around them
  • Don't spread to other parts of the body
  • Can be removed and can grow back very slowly (but usually don't grow back)

Malignant growths (prostate cancer):

  • May sometimes be a threat to life
  • Can infect nearby organs and tissues (such as the bladder or rectum)
  • Can spread (metastasize) to other parts of the body (like lymph nodes or bone) 
  • Often can be removed but sometimes grow back

Prostate cancer cells can spread by breaking away from a prostate tumor. They can travel through blood vessels or lymph nodes to reach other parts of the body. After spreading, cancer cells may attach to other tissues and grow to form new tumors, causing damage where they land.

When prostate cancer spreads from its original place to another part of the body, the new tumor has the same kind of abnormal cells and the same name as the primary (original) tumor. For example, if prostate cancer spreads to the bones, the cancer cells in the bones are actually prostate cancer cells. The disease is metastatic prostate cancer, not bone cancer. For that reason, it's treated as prostate cancer in bone.

To understand prostate cancer, it helps to know how the prostate normally works.

The Prostate

Male reproductive system
Male reproductive system

The prostate and seminal vesicles are part of the male reproductive system. The prostate is about the size of a walnut and weighs about one ounce. The seminal vesicles are two much smaller paired glands. These glands are attached to each side of the prostate. The prostate is below the bladder and in front of the rectum. It goes all the way around the urethra. The urethra is a tube that carries urine from the bladder out through the penis.

The main job of the prostate and seminal vesicles is to make fluid for semen. During ejaculation, sperm is made in the testicles, and then moves to the urethra. At the same time, fluid from the prostate and the seminal vesicles also moves into the urethra. This mixture-semen-goes through the urethra and out of the penis as ejaculate.

When cancer occurs, it is found in the prostate gland and almost never in the seminal vesicles.