Devesa Examines Cancer Trends, By The Numbers
By Carla Garnett
On the Front Page...
Increasing use of food refrigeration, declining use of certain preservatives, and rising consumption of fresh fruits and vegetables may have led to a reduction in stomach cancer mortality in the United States. That is one of several conclusions epidemiologists have drawn based on studying cancer trends over the last half century, according to Dr. Susan Devesa, who discussed "Variations in Cancer Rates: The Influence of Age, Gender, Race, Time, and Space," during a recent summer lecture series on health disparities. The lectures are targeted each year to NIH's summer students through the Office of Education, NIH Office of Intramural Research. In her lecture, Devesa explained how epidemiologists use statistical data to help predict a nation's healthcare and medical research needs.
The statistics can seem grim, indeed: In the United States this year, more than 500,000 people will die of cancer; more than one million will be newly diagnosed with cancer. This does not include superficial cancers of the skin, Devesa noted. Odds are that one in four males and one in five females will die of cancer. One in two males, and one in three females, will be diagnosed with cancer during their lifetime.
In 1970, the U.S. had close to 330,000 cancer deaths. By 1997, cancer deaths in the nation were up to nearly 540,000, a 64 percent increase. However, Devesa pointed out, Americans are living longer than they did in the 1970's and people's risk of dying from cancer increases the longer they live. The age-adjusted mortality rate (a statistical formula that factors in population growth and aging) rose only about 2 percent during the same time period from 1970 to 1997.
Devesa was an ideal candidate to deliver this particular lecture to this particular audience: A native Washingtonian who graduated from Bethesda-Chevy Chase High School and earned her graduate degrees at Johns Hopkins, she has studied domestic health disparities for more than 20 years. Her 1979 doctoral dissertation, in fact, was on the association of cancer incidence with income and education among blacks and whites. In addition, she herself first became acquainted with NIH more than 30 years ago as a summer student. Since 1993, Devesa has served as chief of the descriptive studies section in the Biostatistics Branch of NCI's Division of Cancer Epidemiology and Genetics.
After providing data on cancer in general, Devesa examined particular forms of the disease in several populations and in a number of selected geographic areas; she then compared and contrasted rates among them. She showed data that help epidemiologists make observations and predictions about disease trends, often leading to formation of public health policy.
For instance, she showed a slide that presented the lung cancer death rates in men between 1930 and 1996. Lung cancer has been the leading form of cancer death among American men since the early 1950's, rising rapidly until the rates began to drop for the first time in 1991. That decline corresponds with a 30-year lag time between peak tobacco usage by men in the 1960's. The first Surgeon General's Report on Smoking and Tobacco Use was released in 1964, she reminded the audience. Similarly, Devesa noted, increased cigarette smoking by women over the past few decades has led to a steady rise in lung cancer deaths among females; lung cancer surpassed breast cancer in 1987 as the leading cause of cancer death in women. "We have yet to see the peak in lung cancer deaths among women," she observed.
Lung cancer deaths were not the most frequent cancer deaths early in the 20th century, she pointed out.
"In the past, stomach cancer was the most frequent form of cancer death in men, but the rates have declined over most of this century," she said. "From 1950 through the late 1980's, colorectal cancer was the second most frequent form of cancer death among men, but in recent decades, prostate cancer has risen and surpassed colorectal cancer as the second leading form of cancer death in men." In women, uterine cancer was the most frequent form of cancer death in the early decades of the 20th century; breast cancer was the leading cancer from the 1950's through 1987, when it was surpassed by lung cancer.
A look at slides taken from color-coded geographic maps included in NCI's new Atlas of Cancer Mortality in the United States, 1950-1994 was also enlightening. The map presenting lung cancer mortality rates among white males during 1970-1994 revealed elevated rates in the southeast quadrant of the U.S., largely reflecting the prevalence of cigarette smoking. The map for 1950-1969 had revealed elevated rates in South Atlantic and Gulf Coast areas, subsequently linked to asbestos exposure in shipbuilding counties during World War II.
"Everything I have presented so far has been based on mortality data, derived from death certificates," Devesa said. "To get information on who is being diagnosed with cancer to calculate incidence rates, we need to review hospital records and pathology reports quite a different data collection system. However, we do not yet have a national cancer incidence registry." The NCI supports the Surveillance, Epidemiology and End Results (SEER) program, which was established in 1973 in response to the enactment of the 1971 National Cancer Act and has supported nine population-based cancer registries around the nation.
Devesa then presented data on racial/ethnic differences in rates. Prostate and lung cancer rates among men were highest among African Americans, followed by white non-Hispanics, and lower yet among white Hispanics, Asian-Pacific Islanders and American Indians. Among women, there was little difference in lung cancer rates between white non-Hispanics and African Americans, whose rates were higher than among the other minority groups. The highest incidence of breast cancer was among white non-Hispanics and of cervix uteri cancer was among white Hispanics.
Devesa said the nation is seeing some progress in lowering rates for some cancers. She noted that substantial decreases have occurred in incidence and mortality rates for cervical cancer in black and white females, largely related to detection of early-stage and premalignant disease by Pap smear and subsequent successful treatment, although rates remain higher in blacks. One type of cancer for which whites have higher incidence and mortality rates is non-Hodgkin's lymphoma, Devesa said. In addition, rates have been rising for several decades, but researchers do not yet fully understand why.
Five-year relative survival rates vary considerably by form of cancer. Rates were less than 20 percent among whites and blacks diagnosed with lung cancer, 86 percent for white women and 71 percent for black women with breast cancer, 94 percent for white men and 87 percent for black men with prostate cancer, and 72 percent for white women and 59 percent for black women diagnosed with cervical cancer. Rates also vary by stage of disease at diagnosis. For example, among breast cancer patients, survival rates ranged from 97 percent to 21 percent depending on whether the disease was localized or had spread at the time of diagnosis.
Devesa concluded by pointing out the opportunities for improvement presented by the epidemiological data. In terms of primary prevention, she said avoidance of exposure to carcinogens and behavior modification may help to reduce the incidence and mortality rates. Only a small proportion of cancers are believed to be hereditary, she said. Secondary prevention efforts namely, diagnosis of preinvasive and early-stage disease will help lower the mortality rates of a number of cancers, she said.
"Epidemiologists suggest that an increased use of refrigeration and declining use of food preservatives over the last half century may have led to the decline in stomach cancer deaths," she said, giving an example of behavioral changes leading to better cancer numbers. "Just think, at one point in our nation's history, more than 60 percent of men smoked. Now, less than 30 percent of men smoke." Clearly, she said, behavior modification through public education about the dangers of smoking helped to reduce the number of smokers, resulting in a peaking of the lung cancer rates among men, not yet seen among women.
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