The Ki-67 Proliferation Index in Tertiary Lymphoid Structures as a Predictor of Survival Outcomes in Patients with Resectable Non-Small Cell Lung Cancer

Background & Objectives : Although the presence of tertiary lymphoid structures (TLS) has been associated with improved immunotherapy efficacy across multiple solid tumors, the prognostic significance of proliferative activity within TLS in patients with resectable non-small cell lung cancer (NSCLC) remains unclear. This study aims to evaluate the predictive value of Ki-67 expression within TLS for survival outcomes in patients with NSCLC and to explore the association between TLS maturity and the cellular proliferation index within these structures. Methods : Postoperative paraffin-embedded pathological specimens from 88 patients with NSCLC were analyzed. Hematoxylin-eosin (H&E) staining and immunohistochemistry (IHC) were performed to evaluate the presence, spatial distribution, and number of TLS. Multiplex immunofluorescence (mIF) staining was used to assess TLS maturity. Kaplan-Meier survival analysis was conducted to determine the prognostic significance of TLS maturity and the cellular proliferation index within TLS. Results : Tumor-associated TLS were identified in the tumor microenvironment of 74 (84.1%) of the 88 patients. The mature TLS was significantly associated with improved recurrence-free survival (RFS) in patients with NSCLC ( P = 0.0068). The cellular proliferation index within TLS demonstrated a significant positive correlation with TLS maturity. Compared with early-stage TLS and primary follicular-like TLS, secondary follicular-like TLS exhibited a significantly higher proliferation index ( P < 0.0001). Furthermore, a high TLS cellular proliferation index was predictive of favorable RFS in patients with NSCLC ( P = 0.0231). Multivariate analysis further indicated that a low TLS cellular proliferation index was an independent adverse prognostic factor for RFS (HR= 1.9040, 95% CI: 1.054-3.440; P = 0.0330). Conclusion : This study demonstrates the prognostic relevance of the cellular proliferation index within TLS in the tumor microenvironment of NSCLC. A high TLS cellular proliferation index was significantly associated with prolonged RFS. These findings suggest that an elevated TLS cellular proliferation index may contribute to improved clinical outcomes by promoting TLS maturation and enhancing antitumor immune responses.