Of note, the diagnostic sensitivity, specificity, DOR, and AUC for small cell lung cancer were 0.90 (0.84–0.94), 0.95 (0.94–0.97), 249.5 (103.94–598.8), and 0.98, respectively, showing that RASSF1A methylation was a promising biomarker for diagnosing small cell lung cancer with both high diagnostic and exclusion value. Here, RASSF1 is linked to small cell lung carcinoma.