The National Cancer Institute has published its first monograph focusing on the effects of socioeconomic status on cancer.
Area Socioeconomic Variations in U.S. Cancer Incidence, Mortality, Stage, Treatment, and Survival, 19751999, published in July, is aimed at helping public health researchers and policy-makers track the nations progress toward reducing the cancer burden and health disparities among the U.S. population.
"The impact of socioeconomic factors on cancer has been less well studied in the past than for other chronic diseases such as heart disease, diabetes, stroke, and respiratory conditions," noted Gopal Singh, Ph.D., the monographs lead author. "And the association is a complex one."
Singh and colleagues examined incidence, mortality, stage at diagnosis, and survival for all cancers combined and for breast, cervical, colorectal, lung, and prostate cancers and melanoma. They also studied surgical treatment patterns in breast, lung, and prostate cancers. Mortality data are for the entire U.S. population, and other types of data were extracted from the 11 cancer registries that are part of NCIs Surveillance, Epidemiology, and End Results (SEER) program. They classified counties in a three-tiered system according to the proportion of inhabitants living in poverty. They also analyzed SEER data at the level of the census tract, an area containing about 4,000 residents and designed by the Census Bureau to be relatively homogeneous in socioeconomic status.
About 13% of the U.S. population lives in counties classified as high-poverty, with more than 20% of their population living below the poverty threshold, defined for the 1990 U.S. census as an annual income of $12,674 for a family of four. About 56% of the population lives in counties where between 10% and 20% of residents are below the poverty level (medium-poverty areas), and 31% of the population lives in counties with a poverty level of less than 10% (low-poverty areas).
In a time when U.S. health disparities are a subject of increasing concern, the report includes some troubling findings. In general, Singh said, high-poverty areas were characterized by later-stage diagnosis, poorer survival, and higher mortality rates.
"Even though we see a substantial decline in mortality over time in all [socioeconomic] groups, there is still a considerable gradient" where the poor have worse outcomes, he said. For all cancers combined in men, the mortality rate was 2% higher in high-poverty areas in 1975. But by 1999, the difference had risen to 13%. For women, all-cancer mortality was 3% lower in high-poverty areas than low-poverty areas in 1975, but 3% higher in high-poverty areas in 1999.
Singh said the findings probably reflect a lack of health insurance, lack of access to care, and lack of information about cancer detection and treatment among the poor.
"High-poverty areas have substantially lower rates of mammography and colorectal cancer screening," he said. Residents of high-poverty areas were also less likely to receive optimal surgical treatment for breast, prostate, and lung cancers.
"One thing that struck me was cervical cancer distribution by stage," added coauthor Barry Miller, Dr.P.H. "Its one of the cancers where we know screening is important to catch cases before they become lethal, and great strides have been made in an effort to get all women screened. Yet we still see a socioeconomic differential." While 59.6% of cervical cancer cases were diagnosed at the localized stage in low-poverty areas, the proportion falls to 52.3% in high-poverty areas.
Nancy Krieger, Ph.D., at the Harvard School of Public Health, studies socioeconomic position and disease, and has worked to develop methods of "geocoding" such as those used in the NCI study.
"Its remarkable, and disturbing, to have counties where more than 20% of the residents are below poverty level, and you can see the impact of that on adverse outcomes, particularly for mortality and survival for many cancer sites," Krieger said.
She added that the inclusion of longitudinal data on trends in the report is particularly useful. "One reason why this kind of monograph is so important is it allows us to see how [the impact of socioeconomic status on cancer] plays out over the long termsomething you cant always see in a cross-sectional study."
Because counties are a fairly large unit of analysis and may include substantial socioeconomic variation within them, Krieger said, "its good to see they have some of the census-tract-level data as well" in the NCI study. Yet she said additional detailed analyses at the census tract level are needed. As a participant in the Department of Health and Human Services Cancer Disparities Health Review, Krieger has recommended that the nations cancer registries include geocoding as a routine part of their monitoring.
Among other highlights of the report:
· Women in poor areas are less likely to be diagnosed with breast cancer than women in more affluent areas, with an 18% difference in incidence between high- and low-poverty areas for 19971999. Reproductive patterns, such as earlier childbearing, are believed to reduce risk among poorer women. But while women in poor areas also used to be less likely to die of breast cancer (15% lower mortality rate in 1976), their mortality rate has now surpassed that of women in wealthier areas (17% higher mortality for 19951997). "Breast cancer is simultaneously a disease of affluence and of poverty," Krieger said.
· For prostate cancer, incidence and mortality show socioeconomic gradients in opposite directions: incidence is higher, but mortality lower, in areas with less poverty. From 1975 through 1989, prostate cancer mortality did not vary much by area poverty rates. But since 1990, the authors wrote, "there has been a widening of the area socioeconomic gradient, with men in high-poverty counties in 1999 experiencing a 22% higher prostate cancer mortality than men in low-poverty counties." Singh said this may in part be a result of greater adoption of PSA screening among more affluent segments of the population during the 1990s. Among men in high-poverty areas, 9.1% of cases were diagnosed when they already had distant metastases; for men in low-poverty areas the number was 4.8% (See Stat Bite, p. 1432).
· Both lung and colorectal cancer rates seem to reflect the effects of changing patterns of consumption in American society. In the mid-20th century, cigarette smoking was more common among the affluent, while toward the centurys end it became a habit more associated with lower socioeconomic status. Lung cancer mortality was 7% greater in high-poverty areas in 1975 and 25% greater in high-poverty areas in 1999. Similarly, diets among the poor may once have been healthier than affluent Americans diets, particularly when meat was less affordable. Now, the poor are believed more likely to eat high-fat diets that increase risk for colorectal cancer. The colorectal cancer mortality rate for men in high-poverty areas in 1975 was 12% lower than in low-poverty areas, but by 1999 men in poorer areas had 5% higher mortality.
· Risk for melanomaand death from melanomaincreases with socioeconomic status. Incidence rates were 69% higher for men and 82% higher for women in low-poverty areas during 19971999. Mortality rates were 32% and 25% higher for men and women, respectively, in low-poverty counties in 1999. Singh said this might reflect the fact that lighter-skinned Americans (at higher skin cancer risk) are more likely to be affluent than their darker-skinned counterparts, and they may also have more opportunities to enjoy recreation in the sun.
The report is available on the NCI Website at http://seer.cancer.gov/publications/ses.
![]() |
||||
|
Oxford University Press Privacy Policy and Legal Statement |