An adjustment to the 1997 estimate for new prostate cancer cases

In January 1997, the American Cancer Society estimated that 334,500 new cases of prostate cancer might occur in the United States during 1997.1 That projection was largely influenced by the rapid increase in incidence rates of prostate cancer during the late 1980s and early 1990s, but it also included a sharp decline between 1992 and 1993.2–5 Because recently available rates provided evidence of continued decline, a midyear adjustment to the 1997 projection was deemed necessary. We now estimate that fewer than 210,000 new cases of prostate cancer may be diagnosed in 1997. The original 1997 estimates were based on census data from the US Bureau of the Census and incidence rates from the Surveillance, Epidemiology, and End Results (SEER) Program of the National Cancer Institute (NCI) for the years 1979 to 1993.1 Between 1987 and 1992, the incidence rate of prostate cancer increased 84%, from 102.9 (age-adjusted to the 1970 US standard population)1 per 100,000 to 189.4 (age-adjusted to the 1970 US standard population) per 100,000; however, between 1992 and 1993, the incidence rate declined 11%.2 Incidence rates of prostate cancer for the years 1994 and 1995 also declined (unpublished SEER data). However, these rates were not available when the original estimates were computed, and the 1995 data are preliminary. Based on the new information, the ACS and the NCI concluded that the original 1997 projection was too high. We developed an adjusted estimate using a linear projection and assuming that the number of prostate cancer cases would decline initially, and then continue to increase at rates in effect before widespread use of prostate-specific antigen (PSA) screening. The revised estimate of new prostate cancer cases that resulted from this approach was 209,900. The adjusted estimates of new prostate cancer cases and the revised estimates of total cancer cases in 1997 are shown for the entire United States in Table 1 and for individual states in Table 2. The rapid increase in prostate cancer incidence that occurred in the late 1980s and early 1990s and the decline that followed recently are probably related to the effects of PSA screening.6 When a screening test such as PSA is rapidly and widely adopted by the population, the incidence rate for the disease under scrutiny increases as the result of diagnosis of cancers at an early stage that otherwise would have been diagnosed at a later time. Once this pool of cases has been depleted, the incidence rate declines. We do not know yet whether the incidence rate of prostate cancer will (1) decline to the level seen before the initiation of PSA screening or (2) approach a different level related either to real changes in incidence or to the diagnosis of cases that otherwise would not have come to attention.7 Because the adoption of PSA screening varied by geographic location and time,6 the declines in prostate cancer incidence also are likely to vary by geographic location and time. Our estimates are based on cancer incidence data collected by the SEER program in the states of Connecticut, Hawaii, Iowa, New Mexico, and Utah and in the metropolitan areas of Atlanta, Detroit, Seattle, and San Francisco. The incidence of prostate cancer in these geographic locations is likely to differ from that for the entire United States because of differences in demographics. From 1989 to 1993, the SEER estimate of prostate cancer incidence (154.5 age-adjusted to the 1970 US standard population per 100,000) was higher than the rate of 142.9 (age-adjusted to the 1970 US standard population) per 100,000 reported by the North American Association of Central Cancer Registries (NAACCR) for the same time period.8 The NAACCR incidence rate included all SEER registries plus the 10 state registries that met NAACCR reporting standards. We do not know whether this difference was influenced by the extent of PSA screening in the different geographic locations or was the result of different and changing rates of prostate cancer, different levels of case reporting, or some combination of these factors. Because changes in PSA screening and incidence rates are occurring at present, making forecasts of the number of new prostate cancer cases for upcoming years is complicated, and the resulting projections will not be precise. The rapid increase in prostate cancer incidence in the late 1980s and early 1990s and the decline that followed recently are probably related to the effects of PSA screening.