Tumour-infiltrating lymphocytes and response to neoadjuvant letrozole in patients with early oestrogen receptor-positive breast cancer: analysis from a nationwide phase II DBCG trial

Abstract

Background The presence of tumour-infiltrating lymphocytes (TILs) is associated with response to neoadjuvant chemotherapy among patients with triple-negative and HER2-positive breast cancer. However, the significance of TILs is less clear in luminal breast cancer. Here, we in postmenopausal patients with primary oestrogen receptor-positive (ER+), HER2 normal, operable breast cancer assessed the importance of inducing TILs during 4 months of letrozole on response in a neoadjuvant phase II study. Methods Participants were postmenopausal women with ER+, HER2 normal operable breast cancer assigned to 4 months of neoadjuvant letrozole. Pretreatment core biopsies and surgical specimens were assessed centrally for the percentage of TILs on haematoxylin and eosin-stained slides according to the International Immuno-Oncology Biomarker Working Group on Breast Cancer guidelines. Pathological response was assessed by the Residual Cancer Burden (RCB) index and a modified Miller-Payne grading system and was analysed according to change in TILs. Results Tumour specimens were available from 106 of the 112 patients treated per protocol. TIL concentration increased with mean 6.8 percentage point (p < 0.0001) during treatment (range - 39 to 60). An increase in TILs was significantly associated with pathological response with OR = 0.71 (95% CI 0.53-0.96; p = 0.02) per 10% absolute increase for pathological response and correspondingly OR = 0.56 (95% CI 0.40-0.78; p = 0.0007) for lower RCB index per 10% increase. Conclusion Increasing TILs during letrozole was significantly associated with a poor treatment response. An increase in TILs during endocrine therapy might imply immunogenicity, and these patients could be targetable by immunotherapy.