Background: There is limited research evaluating real-world platinum sensitivity and treatment patterns among patients with limited vs. extensive stage small cell lung cancer (SCLC). Methods: We identified patients with SCLC in 2017 using ICD-10 diagnosis (Dx) and drug codes in the 2016-20 Medicare Parts A/B/D 100% Research Identifiable Files. Patients had 1+ lung cancer Dx and continuous enrollment in Parts A/B/D from the month prior to first Dx in 2017 (index) through 2020 or death. Patients with evidence of end-stage renal disease, prior lung or any metastatic cancer Dx within 12 months of index, lung resection/lobectomy, or use of a drug indicated only for non-SCLC or lung neuroendocrine cancer per NCCN guidelines were excluded. Use of systemic therapies cisplatin (ci), carboplatin (ca), etoposide intravenous (etIV), atezolizumab (at), durvalumab (du) and irinotecan (ir) were observed. Patients included in our study were treated with first-line NCCN Category 1 preferred regimens: ca/etIV, ca/etIV/at, ca/etIV/du, ca/ir, ci/etIV, ci/etIV/du, or ci/ir. First line of therapy (LoT1) was defined based on the first claim for a first-line regimen administered within 90 days following or up to 14 days before index. The end of LoT1 was defined as the earliest of death, 32 days after the last administration, or the start of a second line of therapy (LoT2). Patients initially treated with ca/etIV/at, ca/etIV/du, ca/ir, ci/etIV/du, or ci/ir regimens were flagged with extensive stage disease. Patients not receiving these regimens were classified as limited stage disease if they had 15+ days of radiation therapy over a 6-week period during or within 60 days of LoT1. Patients were deemed platinum sensitive (PS) if we did not observe a LoT2, hospice, or death within 6 months of LoT1. Uncategorizable patients were flagged Status Unknown (SU). All other patients were deemed platinum refractory (PR). Results: We identified 3,772 SCLC patients receiving NCCN Category 1 preferred regimens: 43% (1,607) had limited stage, and 57% (2,165) had extensive stage at index. Among patients with extensive stage, 71% (1,541) were PR compared with 34% (548) of patients with limited stage. On average, patients with extensive stage had fewer platinum cycles in LoT1 than those with limited stage. Conclusions: More platinum refractory patterns were observed among Medicare FFS patients with extensive stage SCLC than among patients with limited stage SCLC. Patients with extensive stage SCLC also underwent fewer platinum cycles in their first line of therapy.