Prognostic value of tumour-infiltrating lymphocytes based on the evaluation of frequency in patients with oestrogen receptor–positive breast cancer

We investigate the prognostic value of tumour-infiltrating lymphocytes (TILs) based on the evaluation of the present frequency in patients with breast cancer rather than that of the density proposed in previous research. Multiphoton microscopy (MPM) was introduced to label-freely obtain TIL images from a total of 564 patients, and then TILs were redefined as TILs-1 to TILs-3 from MPM images according to the relative positions between TILs, tumour cells and collagen fibres. More seminally, a new method, which was based on the present frequency of TILs-1 to TILs-3, was presented for assessing the predictive ability of TILs, and then a tumour-infiltrating lymphocytes score (TILs-score) for each patient was obtained by ridge regression analysis. Data results from Cox proportional hazards regression analysis showed that the TILs-score was an independent prognostic factor for both disease-free survival (DFS) and overall survival (OS) in the complete cohort (n = 564), oestrogen receptor (ER)–positive subgroup (n = 352) and ER-negative subgroup (n = 212), but was more suitable for the ER-positive subgroup. Furthermore, the nomogram model combining the TILs-score with independent clinical factors further improved the predictive ability for the ER-positive subgroup: area under the curve (AUC) at 5-year DFS (OS) and hazard ratio (HR) for DFS (OS) in the training cohort increase from 0.735 (0.785) to 0.814 (0.830) and from 3.156 (5.845) to 4.643 (7.006), respectively, and in the validation cohort from 0.749 (0.748) to 0.804 (0.830) and from 3.104 (3.701) to 3.729 (5.132), respectively. The TILs-score is an independent prognostic factor and displays a strong prognostic value for ER-positive breast cancer. To our knowledge, this is the first time to use MPM for studying the prognostic value of TILs in breast cancer. •A new method is presented for tumour-infiltrating lymphocytes score (TILs-score).•The TILs-score is an independent prognostic factor.•The TILs-score is more suitable for oestrogen receptor-positive breast cancer.