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What is Cancer
Cancer is a group of more than 100 diseases caused by the uncontrolled growth and spread of abnormal cells. Tumors, or abnormal growth of tissue, may be benign or malignant. Benign tumors are usually slow-growing and not life-threatening, whereas malignant tumors (or cancers) are made up of cells with abnormal genetic material (or DNA) and grow more rapidly. Malignant tumors have a tendency to invade neighboring tissues or organs and to travel and grow in other areas of the body (i.e. to metastasize). If the spread of the cancer is not stopped, cancer cells invade vital organs which can result in death. Cancer cells may remain at their original site (local stage), spread to an adjacent area of the body (regional stage), or spread throughout the body (distant stage). Cancers at the local, regional or distant stage are considered invasive. A very early cancer found in only a few layers of cells, called in situ cancer, is considered non-invasive. (Please see the Glossary for definitions of many of these terms.)
What Causes Cancer
Cancers are thought to be caused by a variety of factors working alone or in combination. Some cancers are caused by external factors such as tobacco, diet, certain chemicals, radiation, and viruses and some by internal factors such as hormones, immune conditions, and inherited genetic mutations. Usually ten or more years pass between exposure to a factor that causes cancer and the detectable disease.
Cancer Incidence and Mortality in the U.S.
Cancer is the second leading cause of death in the U.S., with 1,228,600 new cases and 564,800 deaths estimated for 1998. Over the past 50 years, the death rate from cancer has increased due mainly to a large rise in lung cancer death rates resulting from smoking. During the past few years cancer rates have begun to decrease, possibly as a result of healthier lifestyles, particularly decreases in smoking. Cancer occurs in people of all ages, but its occurrence increases greatly in people over 45 years of age. However, it is also the leading cause of non-accidental death among U.S. children under 15. Men have a higher mortality rate due to cancer than women, and blacks have the highest cancer mortality rate of any major racial group. In the U.S., men have about a 1 in 2 lifetime risk of developing cancer and women have about a 1 in 3 lifetime risk. A much higher percentage of people diagnosed with cancer now are surviving than people diagnosed with cancer in earlier years. Now, about four of every ten people diagnosed with cancer will survive for at least five years.
Incidence in the U.S.
Breast cancer is the most common type of cancer among women in the U.S., accounting for 30 percent of the newly diagnosed cases of cancer among women each year. About 178,700 new cases are estimated for 1998 in the U.S. Approximately one in eight women in the U.S. will have breast cancer at some time in her life, according to the American Cancer Society. The age-adjusted incidence rate of breast cancer among women in the U.S. steadily increased between 1940 and 1987, especially between 1982 and 1987, but has stabilized since 1987 at about 110 newly diagnosed cases per 100,000 women a year. Many researchers believe that some of the increase in breast cancer incidence since 1940 may be due to an increase in the proportion of women who have known risk factors for breast cancer, such as giving birth to the first child later in life and having fewer children. Another possible reason for the increase in the incidence of breast cancer, especially from 1982 to1987, is that more women are using breast cancer screening methods such as mammography that identify breast cancer early. Thus, breast cancers that would have been diagnosed in later years (after 1982-1987) were diagnosed earlier. Breast cancer is rare among men; about 1,600 new cases of breast cancer in men are estimated to occur in 1998 in the U.S., representing 0.25 percent of the total estimated cancers in men.
Mortality in the U.S.
Breast cancer is the second most common cause of death due to cancer in women in the U.S. (lung cancer has recently become the most common) with 43,500 deaths estimated nationwide for 1998. The mortality rate of breast cancer among women is declining. The reasons for the decline are believed to include earlier detection which enables more successful treatment. The five-year relative survival rate for localized breast cancer is 97 percent, for regionally spread breast cancer it is 76 percent, and for women with distant metastases it is 21 percent.
Risk Factors for Breast Cancer Among Women
Many risk factors for breast cancer are known.
The above risk factors partly explain the cases of breast cancer among women.6 Pesticides and other chemicals which mimic or modify the action of estrogens are currently under study by various research institutions. Also under study are a diet high in fat, physical inactivity, hormone replacement therapy, genetic factors, and gene-environmental interactions.
Risk Factors for Breast Cancer in Men
The causes of male breast cancer are not as well understood. Some factors thought to increase the risk of male breast cancer are excess weight in young adulthood, gynecomastia (abnormal swelling of the breasts), Klinefelter=s syndrome (an extra X chromosome), and undescended testes; all possibly related to higher levels of estrogen. Men with a family history of breast cancer, especially a female relative who developed breast cancer before age 45, are at higher risk of breast cancer. High doses of ionizing radiation also can cause male breast cancer. It is thought that the lower estrogen levels in men compared to women may partially explain the much lower rate of breast cancer in men compared to women.
Given the known risk factors for breast cancer, opportunities for prevention are limited. The following should be studied further to see if they reduce the risk of breast cancer: moderate physical activity, a diet low in fat and high in fiber, weight control (particularly in women after menopause), and limited consumption of alcoholic beverages. A study of the use of tamoxifen, a drug that is prescribed for women who have had breast cancer to prevent recurrence, indicates that tamoxifen may prevent breast cancer in high risk women. However, there is concern that tamoxifen may have serious short- and long-term side effects. Other medications which may have similar benefits but are less hazardous are under study.
For now, early detection and treatment are the best means to increase survival and reduce mortality due to breast cancer. Mammography, breast examination by a nurse or physician, and breast self-examination, are all methods to detect breast cancer early. Mammography is especially important because it can detect early breast cancers that even very skilled health practitioners may miss. Appendix I contains recommendations from the American Cancer Society for women about using these methods of early detection. Appendix II has information on the New Jersey Breast and Cervical Cancer Control Initiative which provides for free screening of eligible women in New Jersey.
For additional free information on breast and other cancers these organizations may be contacted: