Cancer (medicine)

D

Population Demographics

Population studies show that a person’s age, race, and gender affect the probability that he or she will develop cancer. Most cancers occur in adults middle-aged or older. The risk of cancer increases as individuals age because genetic mutations accumulate slowly over many years, and the older a person is, the more likely that he or she will have accumulated the collection of mutations necessary to turn an otherwise healthy cell into a cancerous cell. More than three-fourths of all cancers in North America are diagnosed in people over age 55.

Statistics show that men are more likely to develop cancer than women. In the United States, nearly half of all men will develop cancer at some point in their lifetimes, whereas slightly more than one-third of women will. Cancer statistics for Canada are similar. Stomach cancer is nearly twice as common in men as in women, as are certain types of kidney cancer. However, the reasons for the discrepancy between the sexes are unknown.

Some cancers are more prevalent in particular races than others. In the United States, for example, bladder cancer is twice as common in white people as in black people. White women are slightly more likely to develop breast cancer than are black women, but black women are more likely to die of the disease. Asian, Hispanic, and Native American women have the lowest breast cancer risk. On the whole, African Americans, especially men, are more likely to develop cancer—and more likely to die from it—than members of any other group in the United States. Reasons for the discrepancies between races are still not entirely clear, but many epidemiologists trace them to differences in diet and exercise, unequal access to medical care, and exposure to carcinogens.

IV

Types of Cancer

More than 100 types of cancer develop in the various organs in the body. Cancers are described according to where in the body the cancer originated, what type of tissue it originated in, and what type of cell it started in. For example, breast cancer describes any cancer that originated in the breast. If the cancer spreads to a new organ, such as the lungs, the tumor is called metastatic breast cancer, not lung cancer.

---

---

Each organ in the body is composed of different types of tissue, and most cancers arise in one of three main types—epithelial, connective, or blood-forming tissue. Carcinomas are cancers that occur in epithelial tissues—the skin and inner membrane surfaces of the body, such as those of the lungs, stomach, intestines, and blood vessels. Carcinomas account for approximately 90 percent of human cancers. Sarcomas originate in connective tissues—such as muscle, bone, cartilage, and fat—that support and connect other parts of the body. Much rarer than carcinomas, sarcomas account for less than 2 percent of all cancers. Leukemias develop in blood cells, and lymphomas originate in the lymphatic system. Combined, these cancers of the blood-forming tissues account for about 8 percent of all human cancers.

Cancers are further identified according to the type of cell affected. For example, squamous cells are flat, scalelike cells found in epithelial tissue. Cancers that originate in these cells are called squamous cell carcinomas. Adenomatous cells are glandular or ductal cells, and carcinomas that originate in these cells are called adenocarcinomas. Sarcomas that develop in fat cells are called liposarcomas, and those that develop in bone cells are called osteosarcomas.

A

Prostate Cancer

Cancer of the prostate gland, a walnut-sized organ surrounding the urethra in men, is the most common cancer among men in North America, after skin cancer. For unknown reasons, the prevalence in black men is nearly twice as high as in white men. Prostate cancer risk increases with age, and some evidence suggests that high-fat diets may increase the risk of developing the disease.

Most prostate cancers are adenocarcinomas, cancers that arise in glandular cells of the prostate’s epithelial tissue. Prostate cancers usually progress slowly and produce no symptoms in the initial stages. Eventually, the tumor may enlarge the prostate gland, pressing on the urethra and causing painful or frequent urination and blood in the urine or semen. Sometimes 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 of the prostate or prostate enlargement, a natural result of the aging process. The prognosis for men diagnosed with prostate cancer is excellent if it is caught and treated early.

B

Breast Cancer

Breast cancer is the most common type of cancer in women, and the second most common cancer in North America. The majority of cases occur in women over 50, and as with most cancers, the risk of developing breast cancer increases with age. An American woman who lives to age 90 has a one in eight chance of developing breast cancer. Breast cancer strikes men as well as women, but male breast cancer accounts for less than 1 percent of all breast cancer cases. Cancer researchers have found that approximately 5 percent of all breast cancer cases are associated with inherited mutations in genes such as BRCA1, BRCA2, and p53. The protein HER-2 (also called HER2/neu), produced by oncogenes, is present in about one-third of all breast cancers. Other risk factors include a family history of the disease, early onset of menstruation, late menopause, never having children, or having a first child after age 30, conditions that extend the duration of estrogen exposure in the body.

In 2006 researchers reported a 7 percent decrease of the incidence of breast cancer in the United States from 2002 to 2003. They attributed this decrease to declining use of hormone replacement therapy, which many women took to lessen the effects of menopause. A study linking HRT with an increased risk of breast cancer, reported in 2002, caused many women to stop using the therapy.

Most breast cancers are first detected as an unusual mass or lump in the breast. If the cancer is detected and treated early, the odds of recovering from breast cancer are extremely good.

C

Lung Cancer

Lung cancer is the third most common type of cancer in North America. Although it ranks below prostate cancer and breast cancer in prevalence, lung cancer is the leading cause of cancer deaths among both men and women in the United States and Canada. The death rate from lung cancer is declining among The five-year survival rate for lung cancer is quite low, but it climbs to about 50 percent if the cancer is detected early.

The single largest risk factor for lung cancer is cigarette smoking, a behavior that accounts for 85 to 90 percent of all cases. The incidence of lung cancer, as well as the death rate, is declining among North American men as a result of the drop in smoking. Lung cancer rates have been increasing among women, who took up smoking in large number during and after World War II. The lung cancer incidence and death rate among North American women has now reached a plateau and is expected to decline, as more and more women have ceased to smoke.

Long-term exposure to secondhand smoke also causes lung cancer. Other major risk factors include workplace exposure to carcinogenic chemicals, particularly asbestos and organic chemicals such as vinyl chloride. Exposure to radon gas and other air pollutants also increases lung cancer risk, particularly among smokers.

Lung cancer often goes unnoticed in its early stages. As the disease develops, a persistent cough may develop or a chronic cough may worsen. Other symptoms include chest pain, shortness of breath, hoarseness, bloody fluid coughed up from the respiratory tract, and frequent bouts of bronchitis or pneumonia. Sometimes the first symptoms of lung cancer are bone pain, headaches, dizziness, or other signs that the disease has metastasized.

	More from Encarta
	•  Presidential Myths Quiz •  Coffee break: Recharge your brain