Evaluation of tumor-infiltrating lymphocytes using routine H&E slides predicts patient survival in resected non-small cell lung cancer

The presence of tumor-infiltrating lymphocytes (TILs) positively impacts the outcome of non-small cell lung cancer (NSCLC) patients. Most previous studies have assessed TILs using different immunohistochemical assays. The purpose of this study was to develop and validate a histopathological scoring model for the assessment of TILs in whole-tissue hematoxylin and eosin (H&E)-stained section slides of NSCLC patients and to evaluate the model in an immunoscore setting. Therefore, TIL was evaluated manually on H&E slides from 537 surgical specimens of primary resected stage I-III NSCLC patients. Using stromal TIL score as a stepwise discrete variable, increasing survival was seen with rising TIL level: disease-specific survival (DSS; P = .008), overall survival (P = .036) and disease-free survival (P = .006). Subgroup analysis revealed that high stromal TILs level was associated with superior DSS (P = .047) in patients with squamous cell carcinoma, but not in patients with adenocarcinoma. Multivariable analysis confirmed that high TIL levels independently predict improved prognosis for all endpoints in the overall cohort. In conclusion, high stromal TIL level is an independent favorable prognostic factor in stage I-III NSCLC patients. The comprehensive histological evaluation conducted in this study may be helpful in streamlining TIL quantification for routine clinical use in a future NSCLC immunoscore setting.