Pulmonary Squamous Cell Carcinoma Dissemination Through Air Spaces (STAS): Clinicopathologic Findings in Different Tumor Origins

Background: Spread through air spaces (STAS) is a recognized histologic pattern of invasion associated with poor prognosis in non-small-cell lung cancer (NSCLC), particularly adenocarcinoma. However, its presence in pulmonary squamous cell carcinoma (SCC), whether primary or metastatic, remains largely unexplored. Given the limited available evidence, this study was designed as an exploratory analysis to evaluate the prevalence and potential prognostic significance of STAS in pulmonary SCC. Material and Methods: In this exploratory retrospective study, we analyzed 57 patients who underwent surgical resection for pulmonary squamous cell carcinoma (P-SCC) at the Department of Thoracic Surgery at the University Hospital Erlangen between 2008 and 2020. The cohort included both primary lung SCC and metastatic SCC to the lung from extrapulmonary sites, primarily from ear, nose, and throat (ENT) tumors. Histological slides were reviewed to assess the presence of STAS, as defined by established morphological criteria. The Chi-square test was used to investigate the presence of STAS. Disease-free survival (DFS) and overall survival (OS) was evaluated using Kaplan–Meier analysis, and the prognostic impact of STAS along other variables were assessed using Cox proportional hazards regression. Results: A total of 57 patients with squamous cell carcinoma (SCC), 22 (39%) had primary lung SCC and 35 (61%) had metastatic SCC from head and neck tumours (ENT). Spread through air spaces (STAS) was detected in 20 patients (35%). Disease-free survival (DFS) differed according to primary tumour location (p-value of 0.009), with higher 1-, 3-, and 5-year DFS in patients with primary lung SCC (86.4%, 77.3%, 63.3%) than in those with head and neck SCC (54.3%, 31.4%, 22.2%). DFS was also significantly higher in patients undergoing solitary resections compared with multiple resections (78.6%, 64.3%, 49.5% vs. 33.3%, 6.7%, not estimable; p-value < 0.001). DFS was slightly longer in STAS-negative patients compared with STAS-positive patients (1-, 3-, 5-year DFS: 64.9%, 51.4%, 40.5% vs. 70%, 45%, not estimable), (median DFS 36 vs. 25 months; p-value of 0.776). Overall survival (OS) was significantly longer in patients with primary lung SCC (median OS 125 months) than in those with head and neck SCC (27 months; p-value of 0.039). STAS-negative patients had also a longer OS than STAS-positive patients (median OS 46 vs. 38 months; HR = 1.11, 95% CI 0.56–2.20; p-value of 0.771). Conclusions: STAS was identified in metastatic pulmonary SCC lesions as well as in primary lung SCC, occurring in approximately one-third of cases. However, due to the limited cohort size and the exploratory univariate design of the study, the prognostic significance of STAS could not be definitively established and requires further investigation in larger, adequately powered studies.