Predictive value of tumor infiltrating lymphocytes (TIL) for response to breast cancer neoadjuvant chemotherapy (NCT).

585 Background: The association of tumor microenvironment immune response with outcome after breast cancer (BC) NCT has been suggested by several studies. However, the relevance of each TIL subpopulation is still controversial. The objective of this study was to evaluate the predictive and prognostic value of TIL before and after NCT in patients with BC. Methods: We analyzed TIL and CD68 cells in pre- and post-chemotherapy biopsies of BC patients treated with NCT (80.4% sequential AC-docetaxel). A tissue microarray with paired pre- and post-NCT biopsies was built, and stained with immunohistochemistry (IHC) for CD3, CD4, CD8, CD20, FOXP3 and CD68. Morphometric analysis (TIL count/mm2) was performed after slide scanning and digitalization. Results: We included 121 consecutive patients with invasive BC, most of them with stages IIB (28%) or IIIA-C (56.4%). IHC phenotype: 50.4% Her2- hormone-sensitive (HS), 13.2% Her2+ HS, 10.7% Her2+ non-HS, and 21.5% triple negative. Pathologic complete response (pCR): 17.4%. Median overall survival (OS) and disease free survival (DFS) has not been reached (median follow-up: 60 months). Higher than median pre-NCT TIL infiltration was predictive of pCR to NCT: CD3 > 172/mm2 (p=0.001; Hazard Ratio [HR]: 9,61, 95% confidence interval [95%CI] 2.49–37.02); CD4 > 67/mm2 (p=0.001; HR: 8.82, 95%CI 2.43–31.96); CD20 > 42/mm2 (p=0.001; HR: 8.71, 95%CI 2.31–32.74). Logistic regression multivariate models including grade and IHC phenotype confirmed the independent predictive value of higher pre-NCT CD3, CD4, and CD20 for pCR. In the group of patients with HS Her2- BC without pCR (n=44), higher infiltration (cut-point: median value) by some TIL subpopulations and by CD68 cells in post-NCT residual tumor associated to lower DFS: CD8 > 37/mm2 (log-rank; p=0.04), CD20 > 14/mm2 (p=0.07) and CD68> 39/mm2 (p=0.06). Conclusions: Higher pre-treatment CD3, CD4 and CD20 TIL predicted pRC in patients with invasive BC receiving anthracyclines and taxanes NCT, while higher infiltration of residual tumor by CD8 associated to worse DFS in patients with HS Her2- BC without pCR after NCT. TIL might be useful as predictive factors in the setting of NCT for BC [Supported by GEICAM-Beca Ana Balil].