Analysis of unexpected small cell lung cancer following surgery as the primary treatment

Purpose: Small cell lung cancer (SCLC) is considered a systemic disease and surgery is generally not recommended to treat it. High heterogeneity within the tumor and preoperative diagnostic capabilities can sometimes fail to identify SCLC correctly, leading to a subset of unexpected SCLC patients that are diagnosed only after pulmonary resections. Methods: We retrospectively reviewed the clinical records of patients who were diagnosed as having SCLC only after surgery between 2008 and 2015 at a single institution. Results: A total of 125 unexpected SCLC patients were identified, including those with pure (p-SCLC; n = 76, 60.8%) and combined (c-SCLC; n = 49, 39.2%) SCLC. Highly differential diagnoses were observed between pre- and postoperative tissue examinations. Sixty-nine (55.2%) patients with postoperatively pathological-proven SCLC, including 31 with p-SCLC and 38 with c-SCLC, were diagnosed preoperatively with poorly differentiated carcinoma (n = 23), squamous carcinoma (n = 14), adenocarcinoma (n = 10), malignant cells with necrosis (n = 10), large cell carcinoma (n = 8), or carcinoid (n = 4). Also, inconsistencies between the clinical (c-) and pathological (p-) stages were found in this cohort, which were less common in patients with preoperative PET examination than those without (24.4% vs. 43.8%; p = 0.032). Multivariable analyses showed that higher p-stage (hazards ratio (HR) = 1.7349, p = 0.0025), sub-lobar resection (HR = 1.9078, p = 0.0395), and a lack of prophylactic cranial irradiation treatment (PCI, HR = 0.3873, p = 0.0057) were unfavorable prognostic factors for overall survival. Conclusion: Non-resection approaches reveal an inadequate diagnosis of SCLC. PET examination facilitates the evaluation of the clinical staging of SCLC. For unexpected SCLC undergoing resection, favorable outcomes can be achieved if radical resection and postoperative PCI are performed.