Overview
Some experts theorize that every man will develop some degree of prostate cancer if he lives long enough. Autopsy studies have shown microscopic evidence of prostate cancer in 15 percent to 30 percent of men over the age of 50 and in 60 percent to 70 percent of men who reach age 80.
The number of men diagnosed with prostate cancer is on the rise, but the death rate from the disease is on the decline. Widespread use of the prostate-specific antigen (PSA) test to screen for prostate cancer and the aging of the population is likely responsible for the increase in prostate cancer cases. Whether the PSA test is also responsible for the declining death rate is a matter of great debate.
A male born today has a 16 percent chance of being diagnosed with prostate cancer at some time in his life and a 3 percent chance of dying of the disease. The good news is that reliable diagnostic tests and numerous treatment options are available for prostate cancer, and death rates from prostate cancer are on the decline.
Anatomy
The prostate is a gland that sits below a man's bladder and in front of his rectum. This gland is the size and shape of a crab apple and surrounds the urethra, the tube that carries urine away from the bladder. The prostate gland has several functions. First, it produces prostatic fluid, which is a component of semen. Second, it serves as a valve to keep both urine and semen flowing in the proper direction. Finally, it pumps semen into the urethra during orgasm.
The prostate is made up of two kinds of cells: glandular (epithelial) cells and smooth muscle cells. The glandular cells produce part of the fluid portion of semen. The smooth muscles contract to push prostatic fluid into the urethra during ejaculation. These muscles are involuntary (not under the control of the individual), like those of the intestines and blood vessels.
The prostate can be divided into three main regions, or zones. Immediately surrounding the urethra is a thin layer called the transition zone; it is surrounded by the central zone, which is followed by the largest and outermost portion, the peripheral zone. Prostate cancer usually occurs in the peripheral zone.
Causes
The underlying cause of prostate cancer is unknown. Like other cancers, however, multiple sequential events over a period of many years are probably necessary to produce a cancerous change in a prostate cell. The first step in the cancer process is the action of an initiator that produces a mutation (alteration) in the genetic makeup of a cell. But the subsequent action of a cancer promoter, which stimulates growth of the abnormal cell, is necessary for cancer to progress.
Risk factors
Age, race, and family history are important risk factors for prostate cancer. Environmental factors such as diet may also play a role. No clear association has been found between the development of prostate cancer and physical activity, smoking, vasectomy, the presence of benign prostatic hyperplasia (BPH), or alcohol intake (although binge drinking may have an effect).
- Age: As a man ages, his risk of having prostate cancer increases dramatically. This age-related increase is greater for prostate cancer than for any other type of cancer. The average age at the time of diagnosis is between 65 and 70, and the average age of death is between 77 and 80.
- Race: The incidence of prostate cancer in the United States varies by race. The rate for white men is 101 per 100,000 each year. Black men are at higher risk (137 per 100,000), and Asian-Americans are at the lowest risk (20 to 47 per 100,000).
- Family history: Studies of identical and fraternal twins show that prostate cancer has a stronger hereditary component than any other type of cancer. Having a first-degree relative (a brother or a father) with prostate cancer doubles the risk of prostate cancer; having a second-degree relative (an uncle or grandfather) with the disease confers only a small risk.
- Genetic alternations: A number of these are linked with prostate cancer. The most studied is known as HPC1. Although some analyses have confirmed that mutations in HPC1 (a region of chromosome 1 that may be involved in protecting against prostate inflammation) increase the risk of prostate cancer, other studies have failed to find an association. Other genes involved in the binding or metabolism of androgens and the body's reaction to inflammation or infection may be important.
Although genes can affect the risk of prostate cancer, other factors are also at work. The likelihood that identical twins (who share all genetic information) will both develop prostate cancer is 19 percent to 27 percent, emphasizing the importance of lifestyle and environmental factors in the risk of prostate cancer. For more on lifestyle and environmental factors, see the prevention section.
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