A novel immune cell signature predicts pathological complete response to neoadjuvant chemotherapy in triple negative breast cancer patients in the Q-CROC3 trial.

Abstract

e12614 Background: Tumor infiltrating lymphocytes (TILs) have been associated with good prognosis and response to neoadjuvant chemotherapy. Several reports have shown that the heterogeneity of tumor infiltrating immune cells affects the response to chemotherapy, with for example low levels of FOXP3 expressing T cells associated with good prognosis and pathological complete response (pCR) to chemotherapy. Methods: We examined different immune cell markers on 52 pre-chemotherapy biopsy specimens obtained from triple negative breast cancer patients undergoing neo-adjuvant chemotherapy from the Q-CROC-03 trial. Slides were stained for CD8, CD3,PD-1, PDL-1, FOXP-3 and Granzyme B using multi-colour immunohistochemistry and automated cell counting of stroma and epithelial counts was conducted using the Vectra/inForm image analysis platform. We had total of 39 variables for analysis and we performed Penalized logistic regression for variable selection. Results: Nine variables were found statistically significant to predict response to chemotherapy, PD1+ stroma counts being the one with the highest probability of association with response. A tree algorithm was then used on all 9 variables to identify the best variable and threshold combination to identify patients who respond to chemotherapy. We separated our cohort in test (25% of samples n = 13) and training (75% of samples n = 39) sets for this analysis. Restricting the tree depth to 2 variables for clinical interpretability identified the combination of average counts of stromal PD1+ and average density of stromal FOXP3+ as predictors of chemo response (accuracy 0.82). Both stromal average PD1+ counts and average stromal FOXP3+ density positively correlated with the levels of TILS. Conclusions: Combining FOXP3 and PD1 protein expression in the stroma of pre-treatment biopsies of triple negative breast cancers receiving neoadjuvant chemotherapy is highly predictive of pCR.