Histopathological features of squamous cell carcinoma of lung neoadjuvant immunotherapy focusing on responses

Objective: To analyze the pathologic features of responses to neoadjuvant immunotherapy of squamous cell carcinoma (SCC) of the lung. Methods: The study included 31 patients with resected lung SCC post neoadjuvant immunotherapy. All patients were recruited from the neoadjuvant anti-PD-1 (Sintilimab) phase Ⅰb clinical trial (ChiCTR-OIC-17013726). The histopathological morphology and different degrees of pathologic response to immunotherapy were evaluated basing on irPRC standard. Results: According to the percentage of residual viable tumor (% RVT), pathologic responses of complete pathologic response (cPR), major pathologic response (MPR) and non-MPR were noted in 19% (n=6), 29% (n=9), and 52% (n=16) of patients respectively. In addition, extensive immune activation phenomena (immune cell infiltration, including infiltration of lymphocytes, plasma cells, foamy macrophages, lymphocyte aggregation and tertiary lymphoid structures formation) and tissue repair features (giant cells, granuloma formation, proliferative fibrosis and neovascularization) were observed in tumor regression bed. Conclusions: Neoadjuvant immunotherapy has favorable effect on lung SCC. Pathologic assessment of resected lung cancer specimens after neoadjuvant immunotherapy shows unique histopathological features consistent with its mechanism.