Population-based incidence and survival figures in essential thrombocythemia and agnogenic myeloid metaplasia: an Olmsted County Study, 1976-1995

To provide basic information about occurrence and outcome of essential thrombocythemia (ET) and agnogenic myeloid metaplasia (AMM), we used the Rochester Epidemiology Project medical record linkage system for residents of Olmsted County, Minnesota. We identified all residents who were diagnosed with ET or AMM from 1976 to 1995. Community inpatient and outpatient medical records were reviewed to verify the diagnosis of ET or AMM, and patients were followed passively through their medical records to determine the outcome after diagnosis. We identified 39 cases of ET and 21 of AMM, with age- and sex-adjusted incidence rates of 2.53 and 1.46 cases/100,000 population annually, respectively. The respective median ages at diagnosis were 72 and 67 years. The female-to-male ratios were 1.8 and 1.6 for ET and AMM, respectively, and when adjusted for age, there was no difference in risk. The median follow-up period was 62.9 months for ET and 33.2 months for AMM. Five- and 10-year survivals were 74.4% and 61.3%, respectively, for ET and were significantly lower than expected for age-matched controls (P = 0.012). Prognosis was worse for AMM, with a median progression time of 7 months and a 3-year survival of 52.4%. This was significantly worse than for age-matched controls (P < 0.001). This study provides population-based incidence and comparative survival figures in ET and AMM.