The prostate is a gland found only in males. As shown in the picture, the prostate is just below the bladder. The size of the prostate varies with age. In younger men, it is about the size of a walnut, but it can be much larger in older men. The tube that carries urine (the urethra) runs through the center of the prostate. The prostate contains cells that make some of the fluid (semen) that protects and nourishes the sperm.
The prostate begins to develop before birth and keeps on growing until a man becomes an adult. Male hormones (called androgens) such as testosterone cause this growth. The prostate usually stays at about the same size or grows slowly in adults, as long as male hormones are present.
Benign prostatic hyperplasia
The inner part of the prostate around the urethra may keep on growing as men get older. This causes BPH (benign prostatic hyperplasia) which can lead to problems passing urine because the prostate can press on the urethra. BPH is not cancer and does not change into cancer. But it can be a real medical problem for some men. If it needs treatment, medicines can often be used to shrink the size of the prostate or to relax the muscles in it, which usually helps with urine flow. If medicines aren’t helpful, some type of surgery, such as a transurethral resection of the prostate (TURP) may be needed. (See the “Surgery for prostate cancer” section for a description of this procedure.)
There are several types of cells in the prostate, but nearly all prostate cancers start in the gland cells. This kind of cancer is known as adenocarcinoma. The rest of the information here refers only to prostate adenocarcinoma.
Some prostate cancers can grow and spread quickly, but most of the time, prostate cancer grows slowly. Autopsy studies show that many older men (and even younger men) who died of other diseases also had prostate cancer that never caused a problem during their lives. In many cases neither they nor their doctors even knew they had it.
Possible pre-cancerous changes of the prostate
Some doctors believe that prostate cancer starts out with very small changes in the size and shape of the prostate gland cells, although this is not known for sure.
Prostatic intraepithelial neoplasia (PIN)
In PIN, 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 gone into other parts of the prostate (like cancer cells would). These changes can be either low-grade (almost normal) or high-grade (abnormal). Almost half of all men have PIN by the time they reach age 50.
The importance of low-grade PIN to prostate cancer is not clear. If low-grade PIN is found on a prostate biopsy, the follow-up for patients is most often the same as if nothing abnormal was seen.
If high-grade PIN has been found on your prostate biopsy, there is about a 20% to 30% chance that you also have cancer in another place in your prostate. This is why doctors often watch men with high-grade PIN carefully and may advise them to have a repeat prostate biopsy, especially if the first biopsy did not take samples from all parts of the prostate.
Proliferative inflammatory atrophy (PIA)
This is another finding that may be noted on a prostate biopsy. In PIA, the prostate cells look smaller than normal, and there are signs of inflammation in the area. PIA is not cancer, but researchers believe that PIA may sometimes lead to high-grade PIN, or perhaps to prostate cancer.