Results
Trend in age-adjusted rates
The age-adjusted incidence (figure 1) indicates a consistently higher rate for males versus females across all years, an increasing trend over the years for males, and a virtually constant rate for females. Accounting for a latency period of 20–40 years for mesothelioma, the increased incidence for males reflects the increased use of asbestos (15) in the United States (figure 2) and the high levels of occupational exposure prior to the late 1960s, when formal workplace exposure limits were established. The age-adjusted rate for males was flat from 1990 through 2000. Projections of future male mesothelioma cases, discussed later, indicate that the number of male cases per year has peaked and is declining.
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| FIGURE 2. Asbestos use (consumption) in the United States and projected numbers of male and female mesothelioma cases based on a birth-cohort and age model estimated from Surveillance, Epidemiology, and End Results (SEER) Program data for two periods, 1973–1992 and 1973–2000.. |
Comparison of trends: data for 1973–1992 versus 1973–2000
A direct comparison of mesothelioma trends based on current data with trends published by Price (7) would not be meaningful because the SEER data have changed since 1992. Two registries were added starting with 1992 data, and mesothelioma counts for the years 1973 through 1991 have been corrected. Therefore, our modeling is based on the current SEER database, first using cases diagnosed from 1973 through 1992 and then using all cases, 1973 through 2000.
Model fits
For each data set (males, females; two time intervals), the predicted values tracked the observed values reasonably well, although there were a few data points with large deviances. The 1973–1992 data sets had 80 data points; the 1973–2000 data sets had 101 data points. When the large deviances were excluded, the statistical fits were acceptable (p > 0.05 based on total deviance) for each model. The numbers of data points remaining were, for 1973–1992, 79 for males and 80 for females and, for 1973–2000, 92 for males and 99 for females.
Lifetime risk of mesothelioma
For females, the lifetime risk of mesothelioma is approximately constant at 3.6 x 10–4 (figure 3). The lifetime risk for males (1973–1992 data, not shown) is a maximum of 2.1 x 10–3 for the 1925–1929 birth cohort and then declines sharply for subsequent cohorts, except for an isolated increase for the 1940–1944 cohort. Regarding the 1973–2000 data, the maximum risk is 1.8 x 10–3 (figure 3). The trend is relatively flat before starting downward after the 1940–1944 cohort.
| FIGURE 3. Lifetime probability (risk) of mesothelioma (pleural + peritoneal) and 95% confidence intervals (vertical bars) based on a birth-cohort and age model estimated from 2003 Surveillance, Epidemiology, and End Results Program data covering 1973–2000 |
Projected number of mesothelioma cases
For the two data sets, mesothelioma projections for females (figure 2) are virtually identical. Although the age-adjusted rate for females is constant, the number of mesothelioma cases increases slightly over time as a function of population size and shifting age distribution. Currently (2003), the annual estimate of female mesothelioma cases is approximately 560.
The trend for males in both data sets peaks in the 2000–2004 time frame at slightly more than 2,000 mesothelioma cases (figure 2). The 1973–2000 model shows fewer mesothelioma cases than the 1973–1992 model during the peak years, but not overall. The total numbers of male mesothelioma cases projected for 2003 through 2054 are 70,990 for the 1973–2000 data and 73,892 for the 1973–1992 data.