About the Prostate

Only men have a prostate. As shown in the picture below, it's a walnut-sized gland located in front of the rectum and underneath the urinary bladder. The prostate's job is to make some of the fluid that protects and nourishes sperm cells in semen. Just behind the prostate gland are the seminal vesicles that make most of the fluid for semen. The urethra, which is the tube that carries urine and semen out of the body through the penis, runs through the prostate.

The prostate starts to develop before birth and continues to grow until a man reaches adulthood. This growth is fueled by male hormones (called androgens) in the body. The main androgen is testosterone. The prostate stays about the same size in adults as long as male hormones are present. In older men, the inner part of the prostate around the urethra may continue to grow, a condition called benign prostatic hyperplasia (BPH). While this can cause problems with urinating because it can press on the urethra (the tube that carries the urine), BPH is not cancer.

Prostate Cancer

Although several types of cells are found in the prostate, over 99% of prostate cancers develop from the gland cells. Gland cells make the prostate fluid that is added to the semen. The medical term for a cancer that starts in gland cells is adenocarcinoma.

Other types of cancer can also start in the prostate gland, including sarcomas, small cell carcinomas, and transitional cell carcinomas. But because these other types of prostate cancer are so rare, if you have prostate cancer it is almost certain to be an adenocarcinoma. The rest of this document refers only to prostate adenocarcinoma.

While some prostate cancers can grow and spread quickly, most prostate cancers grow slowly. In fact, autopsy studies show that many older men (and even some younger men) who died of other diseases also had prostate cancer that never affected them during their lives. In these studies, 70% to 90% of the men had cancer in their prostate by age 80, but in many cases neither they nor their doctors even knew they had it.

Pre-cancerous Conditions of the Prostate

Many doctors believe that prostate cancer begins with a pre-cancerous condition called prostatic intraepithelial neoplasia (PIN). PIN begins to appear in the prostates of some men as early as their 20s. Almost half of all men have PIN by the time they reach 50. In this condition, there are changes in how the prostate gland cells look under the microscope, but the cells are basically still in place -- they don't look like they've invaded other parts of the prostate (like cancer cells would). The changes are classified as either low-grade, meaning the patterns of prostate cells appear almost normal, or high-grade, meaning they look more abnormal.

If you have had high-grade PIN found on a prostate biopsy, there is about a 20% chance that you also have cancer in your prostate. For this reason, doctors often watch men with high-grade PIN carefully and may advise a repeat prostate biopsy, especially if the original biopsy did not take samples from all parts of the prostate.

Another finding that may be reported on a prostate biopsy is atypical small acinar proliferation (ASAP), which is sometimes just called atypia. In ASAP, the cells look like they might be cancerous when viewed under the microscope, but there are too few of them on the slide to be sure. If ASAP is found, there's about a 40% to 50% chance that cancer is also present in the prostate, which is why many doctors advise getting a repeat biopsy within a few months.