SCLC is an aggressive cancer with poor overall survival (OS). LS-SCLC is curable with concurrent chemoradiation (CRT). Cisplatin is the preferred chemotherapy backbone in national guidelines. Unfortunately, many patients with LS-SCLC are elderly, have co-morbidities, and have poor performance status (PS) which preclude cisplatin use. Carboplatin may be a suitable alternative. This analysis evaluates the overall survival (OS) and time to next treatment (TTNT) in LS-SCLC patients receiving concurrent CRT, by 1L platinum use. The study included LS-SCLC patients in the Flatiron Health nationwide de-identified electronic health record-derived database who received CRT in 2013-2019, with follow-up through May 2020. The study excluded patients with no documented visit or medication order within 90 days of diagnosis. Patient characteristics were compared between platinum chemotherapy groups using Wilcoxon rank sum tests and chi-squared tests. TTNT and OS were compared using both unadjusted and inverse propensity weighted Cox proportional hazards models. Propensity scores were built using boosted logistic regression minimizing standardized covariate distances for the covariates smoking history, prophylactic cranial irradiation (PCI), race, gender, age, relevant comorbidities, PS, and creatinine clearance (CrCl). This study included patients treated with carboplatin (n=600) or cisplatin (n=572) in combination with etoposide and RT. Cisplatin patients were younger, had shorter time from diagnosis to radiation, and had less kidney disease. Propensity scores adequately balanced covariates between the two groups. In an unadjusted analysis, OS was greater in the cisplatin compared to the carboplatin group (mOS 22.3 vs. 19.2 m, HR 0.83, p=0.01). In the inverse propensity weighted analysis, this difference was no longer significant (HR 0.93, p=0.41). No differences were seen in TTNT.Tabled 1CarboplatinCisplatinpSMDN600572Age (y)69.1 [62.6, 75.1]65.2 [59.0, 70.2]<0.0010.49ComorbiditiesCardiomyopathy: N (%)12 (2.0%)10 (1.7%)0.9190.02Nephropathy: N (%)27 (4.5%)9 (1.6%)0.0060.17Otopathology: N (%)6 (1.0%)3 (0.5%)0.5500.05Neuropathy: N (%)11 (1.8%)9 (1.6%)0.9060.02ECOG0171 (28.5%)150 (26.2%)0.0830.151160 (26.7%)172 (30.1%)2-355 (9.2%)33 (5.8%)CrCl75.4 [58.3, 99.4]87.9 [70.8, 111.8]<0.0010.41 Open table in a new tab *Categorical variables summarized as N (%) and compared via chi-squared tests, quantitative variables summarized as Median [Interquartile range] and compared via Wilcoxon rank sum tests When balancing on key clinical factors, we observe no statistical difference in OS or TTNT by platinum choice in real-world LS-SCLC patients treated with CRT. Although observational, the results from this large data set are consistent with the hypothesis that either cisplatin or carboplatin is appropriate therapy regardless of health status.