INCIDENCE OF CHRONIC LYMPHOCYTIC-LEUKEMIA IN OLMSTED COUNTY, MINNESOTA, 1935 THROUGH 1989, WITH EMPHASIS ON CHANGES IN INITIAL-STAGE AT DIAGNOSIS

Objective: To determine whether the stage at the time of diagnosis of chronic lymphocytic leukemia (CLL) had changed during a 55-year period . Design: We conducted a study of the cohort of residents of Olmsted C ounty, Minnesota, who had been diagnosed as having CLL during the peri od from 1935 through 1989. Material and Methods: By analysis of medica l records, patients with CLL mere characterized by Rai stage, absolute lymphocyte count, age at diagnosis, need for therapy, and reported ca use of death in nonsurvivors. Trends for these variables were analyzed by decade throughout the study period. Results: The overall annual in cidence rate of CLL per 100,000 population in Olmsted County increased from 2.6 in the 1935 through 1944 period to 5.4 in the 1975 through 1 984 period; however, the increasing rate was found only for those 50 y ears of age or older and was especially dramatic for those 75 years ol d or older. Analysis of Rai stage over time demonstrated an increase i n the proportion of cases diagnosed as Rai stage 0. In addition, the m edian absolute lymphocyte count decreased, the median time to initiati on of therapy increased, and the median age of patients with Rai stage 0 CLL at the time of diagnosis increased over time. Overall, 54% of p atients had received therapy for CLL by the time of last follow-up. Am ong the nonsurvivors, CLL was documented as the underlying or a contri buting cause of death in 69%. Conclusion: The overall increase in CLL was thought to be due to enhanced methods of early diagnosis and impro ved health care for the elderly population. Thus, artifact may best ex plain the observed trend, although we cannot exclude the possibility o f an actual increase in incidence rates over time.