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BACKGROUND Incidence of Myelodysplastic Syndromes in the United States Medicare Population The myelodysplastic syndromes (MDS) are a heterogeneous group of marrow failure diseases associated with serious morbidity with the additional risk of leukemia transformation. The disease course may be indolent or aggressive. MDS is a diagnosis of exclusion. Most de novo patients are symptomatic or present with symptoms of anemia The incidence of these disorders in the United States (US) remain largely conjecture with one available study assessing MDS incidence rates based on 18 Surveillance, Epidemiology, and End Results (SEER) areas. Though a common cause of marrow failure in the elderly population, the incidence of MDS in the US elderly population is unknown. METHODS Approach This retrospective, observational, cohort study was conducted using administrative claims data from a nationally representative sample of Medicare patients, comprising 1.7 million members between Jan 2003 to Dec 2003. Data Source The Medicare Standard Analytic File (SAF) is a randomly-selected 5% sample of all Medicare beneficiaries. Medicare beneficiaries are individuals 65 years, eligible for disability, and/or have end-stage renal disease. Data from Jan 2003 to Dec 2003 were included in the analysis. The dataset is fully de-identified and HIPAA-compliant. The SAF includes claims across different settings of care, such as inpatient, outpatient, physician care, skilled nursing facilities, home health and hospice, durable medical equipment. A denominator file provides demographic and coverage information about the beneficiaries in the dataset. Identification of Study Population The International Classification of Disease, Ninth Revision, Clinical Modification (ICD-9) code 238.7 was used to define patients with primary diagnoses of MDS in 2003. To ensure the study cohort identified represented the incidence population, patients diagnosed with myeloid leukemia (ICD-9-CM codes 205.0, 205.1) or anemias of known causes (ICD-9-CM codes 281, 282, 283, and 284) in 2002 were excluded. The incidence of MDS was described by age, gender, and race (Caucasian, African-American, Hispanic/Latino, and Others). RESULTS We identified 5,594 MDS patients out of approximately 1.7 million patients in the Medicare SAF in 2003. After removing 2,516 patients with myeloid leukemia or anemias of known causes in 2002, we obtained a cohort of 3,078 patients with newly-diagnosed MDS in 2003 (181 per 100,000). Of these cases, 530 (17.2%) had a previous history of unexplained anemia, 172 (5.6%) prior chemotherapy or radiotherapy exposure, and 2,376 (77.2%) were de novo. The median age of the Medicare sample was 76 years (range 24-98). Among individuals aged 80, the incidences of MDS in the Medicare database were 92.6, 132.8, 199.2, 261.5 per 100,000, respectively, confirming the SEER findings of an age effect. Age-adjusted incidence rates for MDS in 2003 were higher among males than females (201.7 per 100,000 in males vs. 165.7 per 100,000 in females, p