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Show Methods The most recent year of reported available cancer data is 1995. Hence, the SEER Program currently has 22 years of follow-up data. This could be a potential problem because some cancer sites with long survival may include living cases diagnosed before the start of the SEER Program. These cases would not be included in a prevalence estimate, such that an overall prevalence estimate would be biased downward. However, we are more interested in prevalence for cases diagnosed within 0-1, 0-5, 0-10, 0-15, and 0-20 years, because health care costs tend to be much more concentrated in the initial years after diagnosis. As a matter of public policy planning, it is of interest to know how cancer prevalence changes as a function of the number of years from diagnosis since treatment and follow-up care are a function of time. So because care typically declines with time survived, it may not be as important to obtain an unbiased measure of overall prevalence as to identify prevalence by time since diagnosis. To compute prevalence for a specific disease (e.g., lung cancer), three types of data are used for each age group (0-4, 5-9, . . ., 80-84, 85+): (a) a column of lung cancer cases for each year, 1973 through 1995; (b) a triangular table of those dying by year of diagnosis (left axis) and year of death (top axis); (c) a triangular table of those lost to follow-up according to year of diagnosis (left axis) and year loss-to follow-up (top axis). A triangular table (d) is then constructed from these data which indicate for each year of diagnosis the number still alive and not lost to follow-up for subsequent years [i.e., (d) = (a) - (b) - (c)]. For example, the number of cases diagnosed in 1980 is adjusted according to the number dying or lost to follow-up in subsequent years to get the number of diagnosed cases still observed in the registry from 1980 to 1995. Since not everyone lost to follow-up dies from their disease, additional steps are needed to provide an estimate of the number alive adjusted for loss to follow-up: we divide (b) by (d) to give the annual death hazards (e); one minus the annual death hazards is estimated (f) [i.e., (f) = 1 - (e)]; actuarial survival (g) is obtained by multiplying cells in (f) cumulatively over columns within each row; and the number alive adjusted for loss to follow-up (h) is obtained by multiplying (a) by each column of (g). Thus, we obtain a triangular table of the estimated number alive in a given year (top axis) by year of diagnosis (left axis) for each age group. These data were combined across age groups to obtain crude prevalence and divided by population values from the United States Bureau of the Census to obtain crude prevalence rates. Results In Table 2, smoking-related cancer prevalence rates are presented per 100,000 for white men in Utah and SEER (with Utah removed), 1993-1995, based on cases diagnosed within the previous 0-1, 0-5, 0-10, 0-15, and 0-20 years. Prevalence rates in the United States are between two and three times greater than the prevalence rates in Utah. The largest difference appears for lung and laryngeal cancers. The smallest difference occurs for cancers of the oral cavity and pharynx. The prevalence rates for the remaining smoking-related cancers are about 100% greater in the United States than in Utah. Only the prevalence rates for cancers of the oral cavity and pharynx become similar between Utah and the United States when conditioned on different times from diagnosis (i.e., from 53% to 9% greater in the United States than Utah when conditioned on 0-1 and 0-20 years from diagnosis, respectively). On the basis of the white male population of 930,301 in Utah in 1995, the estimated number of smoking-related prevalent cases of white men in Utah in 1995 was computed for cumulative years 0-1, 0-5, 0-10, 0-15, and 0-20 of diagnosed cases (Table 3). Estimates are also shown of what the number of prevalent cases would have been in Utah if people in this state had experienced similar cigarette smoking prevalence as in the United States. The difference may be the result of the lower levels of cigarette smoking in Utah relative to the United States. The number of prevalent cases of smoking-related cancers avoided in Utah is striking. For 1995, the lower levels of cigarette smoking in Utah has resulted in an estimated 3,383 fewer smoking-related prevalent cancer cases among white men diagnosed within 0-20 years. 12 |