Descriptive Studies

Abstract

This project conducts a variety of descriptive epidemiologic studies to quantify cancer incidence and mortality; to investigate variations in cancer rates by demographic factors; to examine temporal trends and geographic patterns; and to identify leads for further analytical research. Geographic Variation in Cancer Rates Evaluation of geographic variation in cancer rates may suggest clues to the roles of environmental or cultural influences. Identification of regions at notably high or low risk may indicate areas where more intensive studies might be particularly fruitful. We published a new atlas of cancer mortality in the United States during 1950-94. Data files pertaining to more than 9.5 million whites and 1.1 million blacks who died during 1970-94 and 4.8 million whites who died during 1950-69 from cancer and corresponding estimates of person-years at risk were used by the "Mortality Rate Generator" (MRG) software program to calculate observed and expected counts, age-adjusted rates, and confidence limits for more than 40 forms of cancer by race, sex, time period, and geographic area. Using special graphics software for Windows on a personal computer, more than 250 maps at the county or State Economic Area (SEA) level were generated and included in the atlas. Summary tables and figures were prepared. The updated maps show that the patterns previously observed for several cancers have persisted, such as the broad stretches of high rates for cancers of the breast, colon, and rectum in the Northeast, although the regional variation has diminished somewhat as rates have risen in many areas of the South. For some tumors, the geographic clustering of areas with elevated rates has become more pronounced in the recent time period, as shown for cancers of the corpus uteri, prostate, bladder, and biliary tract. For lung cancer, there have been remarkable changes in the geographic patterns corresponding to regional/temporal variations in smoking trends by sex and race, with the recent emergence of high mortality rates among white men across the South, among white women in the far western states, and among blacks in northern urban areas. The updated geographic patterns should help in formulating etiologic and other hypotheses, and in targeting high-risk populations for further epidemiologic research and cancer control interventions. The text, maps, rates, and the data used to generate the maps are available on the internet (http://www.nci.nih.gov/atlasplus). In addition to an online version of the Atlas, there is a component of the Web site that allows the user to create customized maps based on parameters selected by the user from a menu. The user can determine map color, number of data ranges and the percent of deaths to be included in each range, and ranging method (geographic patterns or time trends). The user can also view an entire state at the SEA or county level, as well as view an individual SEA or county. In each case, a table is included with the map and legend showing the mortality rates, number of deaths, statistical significance, and sparseness status of the selected geographic entity, as well as the ones in which it is contained. The Web site database has been expanded to include county data for Blacks, SEA and state data for Other non-whites, data for the nine 5-year periods from 1950-54 to 1990-94, and four age groups (0-19, 20-49, 50-74, and 75+). Multiple maps displaying geographic patterns or time trends are also available, and these can be animated. Furthermore, dynamic charts displaying mortality rates at the state, SEA, or county level are available. Future enhancements will add rates calculated in a variety of ways. A Web-based version of MRG will be added to the site, enabling the user to have more flexibility in choice of cancers, age groups, and sex and race aggregation. Mapping techniques can highlight the spatial or temporal variations in rates of cancer mortality. In mapping geographic patterns of cancer mortality, spatial units are grouped into categories defined by specified rate ranges, and then the units in each category are assigned a particular color in the map. We examined the consequences of using different ranging methods when comparing maps over several time intervals. Two ranging methods were employed: 1) Ranges defined for individual time interval by the deciles of rates in that interval (ranging within intervals), and 2) constant ranges for all time intervals defined by the deciles of rates for the entire 45-year period from 1950 through 1994 (ranging across intervals). Ranging within time intervals displays geographic patterns and changes in geographic patterns, regardless of time trends in rates. Ranging across time intervals shows temporal changes in rates but with some loss of information about geographic variability. We have been analyzing changes in the geographic patterns for those cancers with substantial variation by area, race, and/or gender. Lung cancer mortality rates among white males in the United States were observed to be elevated during 1950-69 in counties with shipbuilding industries during World War II; risk was found to be associated with asbestos exposure. When we evaluated the geographic patterns in more recent years, 1970-94, for whites and compared them with the 1950-69 patterns, we found that rates generally were higher in shipyard counties than in all nonshipyard counties and in coastal nonshipyard counties for both sexes and time periods, rates increased markedly from 1950-69 to 1970-94 in all groups, with the changes more pronounced in females than males, which may be attributed to the combined effects of low asbestos exposures and changes in smoking behavior. From 1950-1954 through 1990-1994, national melanoma mortality rates among whites increased by 191% and 84% among males and females, respectively. The state-specific rates exhibited a strong but diminishing latitudinal gradient, reflecting the complex interplay of UV radiation levels in each geographic region, the sun-protection behaviors of each generation of males and females in childhood and adulthood, the geographic mobility of the population, and the risk awareness and early detection. Ultraviolet B (UVB) radiation exposure increases the risk of skin cancer in whites. Motivated by indications that United States geographic variation of relative skin cancer risk in blacks approaches that in whites, we used Poisson regression to estimate the risk of skin cancer in blacks as a function of average annual surface-levels of UVB radiation, measured by Robertson-Berger meters. For black males, the age-adjusted relative risk of mortality for a 50% increase in UVB radiation was significantly above one for malignant melanoma, 1970-1994 (1.16; 95% confidence interval, 1.02-1.32) and nearly so for nonmelanoma skin cancer, 1970-1981 (1.18; 95% confidence interval, 1.00-1.39), for which the time period was chosen to avoid AIDS-related deaths from Kaposi's sarcoma. Although the public health implication is uncertain because of the much lower absolute risk of skin cancer in blacks compared with whites, the findings suggest that sunlight exposure increases skin cancer risk in blacks. Research into the geographic patterns and their determinants is ongoing. The geographic patterns for breast cancer mortality have remained remarkably static, but are more pronounced for women older than age 50 years than for younger women. We are examining the age-specific patterns in greater detail over time and comparing them among white and black women. We are using a spatial scan statistic using county-based mortality data from 1970 through 1989 to test whether the elevated regional rates of prostate cancer mortality shown in the recent atlas of cancer mortality were statistically different from rates in the rest of the country and whether they could be explained by known or hypothesized risk factors. Generating New Hypotheses based on Cancer Trends and Demographic Patterns We analyzed the descriptive epidemiology for cancers of the esophagus, bladder and kidney, the leukemias, as well as for cancers among children, among the elderly, and among women, using national and international incidence and mortality data. Our analysis of the recent U.S. trends in lung cancer mortality found an unexpected worsening of the birth cohort trend in risk for people born after 1950; we also found a significant decrease in the slope of the calendar period trend in 1990 for both whites and blacks, observed primarily in people 55 years of age and older. Prostate cancer is the most commonly diagnosed cancer in western men, and incidence is rising rapidly in most countries, including low-risk populations. Age-adjusted incidence and mortality rates from 15 and 13 countries between 1973-77 and 1988-92, respectively, were compared to provide leads for future analytic studies. Large increases in both incidence and mortality rates of prostate cancer were seen for all countries. Increasing incidence rates in the United States and Canada are likely to be due in part to the widespread use of transurethral resection of the prostate and prostate-specific antigen testing, while increases in the Asian countries are probably related to westernization in these low-risk populations. The large disparities in incidence between high- and low-risk countries may be due to a combination of genetic and environmental factors. Future studies are needed to examine gene-gene and gene-environment interactions in various countries concurrently to shed light on the etiology of prostate cancer and to help elucidate reasons for the large differences in risk between populations. In contrast to mortality data, which are limited to specifying the form of cancer, incidence data include information on histologic type of the tumor and in many instances, the subsite of origin. We have used incidence data from the Surveillance, Epidemiology, and End Results (SEER) program to invest