Increased Cancer Incidence Since Mid-1970s Due Mainly to Screening and Smoking; Cancer Death Rates Are Stable or Declining.
The incidence of cancer rose 18.6 percent in men and 12.4 percent in women from the mid-1970s to the early 1990s due mainly to large increases in breast, prostate, and lung cancers in older Americans, according to a study published today by National Cancer Institute (NCI) researchers. Susan S. Devesa, Ph.D., lead author of the study, which appears in the February 1, 1995 issue of the "Journal of the National Cancer Institute," said the increase in breast and prostate cancers is largely due to greater use of early detection techniques because the majority of new cases are being found at early stages of the diseases. The increase in lung cancer is due primarily to cigarette smoking, she said. The authors concluded that environmental hazards do not seem to play a major role in the overall increase in cancer incidence rates.
Devesa and her colleagues evaluated cancer incidence and mortality rates for 28 cancers among men and 30 cancers in women using data from the NCI's Surveillance, Epidemiology, and End Results Program from 1975-1979 and 1987-1991. Comparisons were made between the two time periods with separate evaluations for men and women, each form of cancer, and five age groups for clues as to why rates are changing.
Total cancer incidence increased in all the age groups evaluated by the NCI researchers, and while the common cancers of the breast, prostate, and lung caused the bulk of the increase, incidence rates for several less common cancers are also rising. Increasing rates of non-Hodgkin's lymphoma, melanoma, and nonmelanoma skin cancer (mainly Kaposi's sarcoma) are likely caused by increased exposure to cancer-causing agents.
Much of the increase in non-Hodgkin's lymphoma among young and middle-aged men is related to AIDS, but most of the increase in women and older men remains unexplained and may be related to exposure to pesticides, hair dyes, and other chemicals. Increases in melanoma are due to changing exposures to the sun, and increases in Kaposi's sarcoma are due to AIDS.
Increasing incidence rates of kidney, testicular, and brain cancers are less easily explained. Kidney cancers are moderately related to smoking, but diagnostic improvements may be partially responsible for the rise in incidence rates. Diuretic use is suspected as a possible risk factor. The increasing incidence of brain cancer, mainly in older ages, is due in part to better imaging technology, but further study is needed, especially because there is also an increase in incidence of brain tumors in people under age 35.
The incidence rates of some cancers declined. Colon cancer rates decreased for women and middle-aged men, although rates increased among older men. Increased use of endoscopy (sigmoidoscopy and colonoscopy), whereby pre- cancerous polyps can be found and removed, is likely to have influenced the rates. Cancer of the corpus uteri also continued to decline, most likely because use of unopposed menopausal estrogens (estrogen without progesterone) fell out of favor. Stomach cancer rates continued their decline due at least partly to increasing availability and consumption of fresh fruits and vegetables. NCI recommends eating five or more servings of fruits and vegetables each day.
Cancer death rates rose slightly from 1975-1979 to 1987-1991, only 3 percent among men and 6 percent among women. Increases were limited to older individuals, as rates for men and women under age 55 declined. Among men, mortality rates dropped for brain/nervous system cancer, bone cancers, and leukemia in males up to age 15; for testicular cancer and Hodgkin's disease in young adults; for lung cancer under the age of 55; and for bladder cancer in older individuals. For most other cancers, increases in mortality generally were much smaller than the increases in incidence.
For females, mortality rates declined for leukemia and brain/nervous system, bone, and soft tissue cancers in children; rates dropped for leukemia, Hodgkin's disease, and breast cancer in women age 15 to 34; and breast, ovarian, and colon cancer rates declined in women age 35 to 54. The rising cancer mortality rates among women aged 55 years and older were largely due to lung cancer and to a lesser extent, breast cancer and non-Hodgkin's lymphoma. For blacks, patterns generally resembled those among whites with the exceptions that increases in lung cancer incidence in men and declines in cervical cancer incidence in women played larger roles. Total cancer incidence rates increased in each age group among men, but among women they decreased for ages 15 to 34 and changed little for ages 35 to 54. Testicular cancer and melanoma rates did not change greatly among black men, so rising colon and kidney cancer incidences had more impact on overall trends.
Lung cancer incidence declined among black men ages 35 to 54 and rose among those older, with the increases larger in absolute and relative terms than among white men. Mortality rates for most cancers rose more or declined less among blacks than whites; larger declines in cervix and stomach cancers among blacks were the exceptions. Mortality rates generally declined among blacks under age 55 and increased at older ages.
Thus, the researchers determined that, although the incidence of cancer increased across all age groups among whites and most age groups among blacks, the specific cancers responsible varied by age, sex, and race. Total cancer mortality rose less than incidence and actually declined among those under age 55. Improvements in diagnosis contribute to much of the incidence increases, whereas the mortality trends have been influenced also by improvements in treatment and survival, according to Devesa and her colleagues.
"Increasing exposure to general environmental hazards seems unlikely to have had a major impact on the overall trends, although rising rates for certain tumors have been clearly influenced by changing exposures to tobacco smoking, HIV infection, and sunlight," said Devesa. "The increasing trends for some cancers, such as non-Hodgkin's lymphoma and testicular, kidney, brain, and liver cancers, remain unexplained, and may reflect changing exposures to carcinogens yet to be identified. A more complete understanding of cancer trends and their ultimate reduction will require further research into the origins of specific cancers and the means of prevention, treatment, and control."
Note: On page 157 of the February 1, 1995 issue of "Journal of the National Cancer Institute," the "In This Issue" summary of the study by Devesa et al. contains an error by citing breast cancer instead of lung cancer as attributed to smoking. The last sentence of the first paragraph should read: