The role of liver kinase B1 in small cell lung cancer: association with prognosis and tumor immune microenvironment features

Small cell lung cancer (SCLC) represents approximately 15% of lung cancers and is characterized by dismal prognosis, despite treatment. Chemoimmunotherapy demonstrated improved overall survival compared to chemotherapy alone in extended stage SCLC. However, the clinical benefit of immunotherapy is modest, and predictive biomarkers are needed. Liver kinase B1 (LKB1) is a tumor suppressor kinase and a key cell metabolism regulator. LKB1 downregulation has been associated with a "cold" tumor immune microenvironment (TIME) in non-small cell lung cancer (NSCLC) and showed potential predictive role for immunotherapy. Mutational and non-mutational mechanisms, such as promoter hypermethylation, may account for LKB1 inactivation. The study of LKB1 expression through immunohistochemistry (IHC) can capture LKB1-deficient tumors also in the absence of genomic alterations. Aims of the study were to describe LKB1 expression in SCLC and LKB1 genetical alterations in SCLC, to evaluate the association of LKB1 expression with clinical factors and its prognostic role in SCLC. In addition, we aimed at describing SCLC TIME (presence of CD8+ and FOXP3+ tumor-infiltrating lymphocytes [TILs] and PD-L1 expression), evaluating the association with clinical features and its prognostic role, and the associations of TIME features with LKB1 expression. This is a retrospective monocentric translational study. We collected all SCLCs consecutively treated at our Institution from 1996 to 2020 with formalin-fixed paraffin-embedded tissue for molecular analyses. Immunohistochemistry (IHC) of LKB1 and PD-L1 on tumor cells (TC) and tumor immune-infiltrating cells (TIIC) was performed, TILs were characterized by CD8 and FOXP3 IHC. We evaluated the impact of clinical and molecular features on overall survival (OS) and the association between molecular markers. RNA extraction and quality assessment were performed. LKB1 expression was significantly correlated with good ECOG performance status and limited stage; multivariate analysis confirmed the correlation only with limited stage. Poor PS, weight loss, symptoms at diagnosis, female sex and extended stage were significantly correlated to a worse prognosis, whereas LKB1 positive expression was significantly correlated to a better prognosis. At multivariate analysis, LKB1 positive expression, limited stage and absence of weight loss were confirmed as independent positive prognostic factors. No TIME feature significantly correlated with clinical factors. A significant negative correlation was found between LKB1 expression and the presence of CD8+ TILs. No correlation was found between LKB1 and PD-L1 expression or presence of FOXP3+ TILs. The presence of FOXP3+ TILs correlated with a significantly better OS. Multivariate analysis confirmed the presence of FOXP3+ TILs and limited stage as independent positive prognostic factors. RNA extraction was carried out, however insufficient RNA quality prevented downstream RNA-seq analysis. Future studies will evaluate patients treated with chemoimmunotherapy and will expand TIME evaluation.