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Urology => Prostate Gland => Prostate Cancer
Prostate Cancer
INTRODUCTION
Prostate Cancer, malignancy of the prostate gland, a walnut-sized organ located under the bladder in males. The prostate gland surrounds the urethra, which is the tube that carries urine from the bladder to the penis.
RISK FACTORS
The specific mechanisms that lead to the development of prostate cancer are still unknown, but several risk factors for the disease have been identified. Incidence increases with age-prostate cancer seldom develops before the age of 40 and is chiefly a disease found in men over the age of 65. It is common in North America-affecting 15 percent of American men in their lifetimes-and in northwestern Europe, but rare in South America, the Near East, and Africa. In America, black males, who suffer from the disease 37 percent more often than white males, have the world's highest incidence. A growing body of evidence links diets rich in animal fats with prostate cancer. One study found that human prostate cancer tumors grew only half as fast in mice with diets of 21 percent fat as in mice with diets of 40 percent fat. Dietary differences are believed to explain why the incidence of prostate cancer is 120 times greater in the United States than in China, where fatty foods are not part of the general diet.
Some foods seem to act as a shield against this disease. A nine-year study published in 1995 suggests that tomato-based products protect against prostate cancer, possibly because tomatoes are rich in a substance called lycopene. Lycopene is an antioxidant, a chemical agent that inhibits or retards the cellular process of oxidation. Too much cellular oxidation can be dangerous to a person's health because it produces molecules called free radicals that increase the risk of cancer developing in body tissues. Similarly, the results of a preliminary study recently conducted in Finland indicate that long-term, moderate doses of vitamin E-an established antioxidant-may block the progress of prostate tumors.
Environmental factors, such as workplace exposures to cadmium, have also been associated with increased risk of prostate cancer. Family history plays another important role. Men whose fathers or brothers develop prostate cancer are more likely to develop the disease. Researchers are beginning to identify genetic markers of prostate cancer. For instance, hereditary prostate cancer 1 (HPC1), a gene detected in 1996, appears to significantly predispose men to prostate cancer when inherited in a mutated form.
SYMPTOMS AND DIAGNOSIS
The prostate-specific antigen (PSA) test is the best tool currently available for detecting prostate cancer in its earliest-and most curable-stages. The test measures levels of prostate-specific antigen in the blood. Prostate cancer cells overproduce this protein, causing an elevation of PSA levels in blood. The test, however, cannot distinguish between rises in PSA due to cancer and those related to other factors, including infection or recent ejaculation.
Prostate cancer usually progresses slowly and produces no symptoms in its initial stages. Warning signs may eventually include difficult or painful urination; frequent urination, especially at night; and blood in the urine or semen. Pain in the lower back, pelvis, or upper thighs may signal that prostate cancer cells have spread to the ribs, pelvis, and other bones. All these symptoms, however, may have other causes, such as infection or prostate enlargement, which is a natural result of the aging process.
A physician will suspect prostate cancer if a nodule or other prostate irregularity is felt during a digital rectal examination, in which the physician uses a gloved finger to gently check the smoothness of the rectal lining. The discovery is usually followed by a biopsy, in which a tissue sample is removed from the prostate and examined under a microscope. The American Cancer Society recommends that men have an annual, digital rectal exam beginning at age 50. In addition, men 50 years and older should have an annual PSA test.
Currently there is much debate over whether men of susceptible age (generally, more than 45 years old) should be routinely screened for prostate cancer-for the same reason that women over 40 are periodically screened for breast cancer. Controversy over routine screening stems from a combination of factors, including the facts that the currently available PSA test is not always a reliable indicator and mass screening involves considerable expense. A large study recently conducted in Quebec, Canada, and two major studies now underway in the United States and Europe may clarify these issues. Moreover, recent advances may soon yield tests for precancerous prostate conditions. These tests will be able to distinguish between cells with normal deoxyribonucleic acid (DNA) and those with cancerous DNA. Such tests will enable physicians to predict the development of prostate cancer long before any cancerous cells can be detected.
TREATMENT
Localized cancers may be treated with hormones and anticancer drugs, which shrink the prostate tumor and suppress its ability to metastasize (spread to surrounding tissue). Certain drugs can slow the cancer's growth after it has spread beyond the prostate.
In many cases, a prostatectomy-the surgical removal of the prostate-is performed, often in conjunction with radiation. However, this surgery can cause impotence and urinary incontinence. An alternative is brachytherapy, or seed implant therapy, in which radioactive iodine "seeds" are inserted into the prostate. The procedure, performed under local anesthesia, spares healthy, nearby tissue and appears to be as effective as surgery for men with early stage prostate cancer.
In men over the age of 70, the disease often progresses so slowly that death results from other causes before symptoms of prostate cancer have time to emerge. For this reason, some physicians believe that many patients in this age group can forego surgery and other treatments as long as their condition is regularly monitored-a treatment known as watchful waiting.
Several potential treatments are under investigation including cryosurgery, in which cancer cells are destroyed by freezing temperatures, and gene therapy, which bolsters immune system defenses against cancer.
PROGNOSIS
According to the American Cancer Society, 89 percent of men diagnosed with prostate cancer survive at least five years after diagnosis, and 63 percent survive ten years. If the cancer is discovered while still localized, the five-year relative survival rate (a measure used to monitor persons who are living five years after diagnosis) is nearly 100 percent. About 58 percent of prostate cancers are discovered at this stage.
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