Epidemiologic insights into early-onset myelodysplastic syndrome: A longitudinal SEER analysis (2000-2022)

Abstract Background: Myelodysplastic syndromes (MDS) are clonal hematopoietic disorders marked by ineffective hematopoiesis and peripheral cytopenias, with a heterogeneous clinical course. MDS primarily affects older adults, with a median diagnosis age of near 70 years, but it can occur in young individuals and has been shown to be associated with specific germline and somatic mutations in this age group. Because early-onset MDS is rare, its epidemiology is poorly described. In this study, we used population-based data to better understand epidemiological patterns of MDS diagnosed before age 50. Methods: A retrospective cohort analysis was performed using SEER registry data from 2000 to 2022 to investigate the epidemiology of early-onset MDS among adults aged 20-49 years. Age-adjusted incidence rates were calculated per 100,000 person-years using the 2000 U.S. standard population. Demographic characteristics, including sex, race, and geographic region, were described. State-level incidence rates and race-specific case counts were analyzed. Relative survival estimates at 12 and 60 months were assessed across all early-onset age groups in 5-year intervals using SEER-derived observed and expected survival. Results: A total of 2,856 early-onset MDS cases were identified across 797,888,076 person-years, yielding an age-adjusted incidence rate of 0.4 per 100,000. Annual incidence rates remained stable between 2000 and 2022, ranging consistently from 0.3 to 0.4 per 100,000. The most frequent histologic subtype was myelodysplastic syndrome, not otherwise specified (ICD-9989), accounting for 1,580 cases. Racial distribution showed 1,958 cases among White individuals (rate 0.4), followed by Black (440 cases, 0.6), Asian/Pacific Islander (250 cases, 0.3), and American Indian/Alaska Native (29 cases, 0.3). The highest incidence rates were observed in the SEER registry for Seattle (5.23 per 100,000), New Jersey (4.36), and Kentucky (4.04). Female patients with early-onset MDS had consistently better survival than males, with a 12-month relative survival of 87.6% vs. 79.9% and 5-year survival of 67.6% vs. 52.1%. Relative survival at 12 and 60 months was generally similar across racial groups and between metropolitan and nonmetropolitan areas, with overlapping estimates and no consistent disparities observed. However, smaller subgroups showed wider variation. Compared to adults aged 50 and over, younger patients with early-onset MDS demonstrated substantially higher 5-year relative survival (59.9% vs. 40.3%). Conclusion: Early-onset MDS is rare, with stable incidence over two decades and notable geographic variation, suggesting possible environmental influences. Females had better survival than males, and younger patients fared better than older adults. These findings add to the limited body of research on early-onset MDS, a disease whose subtle clinical presentation makes early diagnosis challenging.