Abstract P3-11-01: Interaction between molecular subtype and stromal immune infiltration dynamics in breast cancer patients treated with neoadjuvant chemotherapy

Purpose: High levels of tumor-infiltrating lymphocytes (TILs) before neoadjuvant chemotherapy (NAC) are associated with higher pathological complete response (pCR) rates, and better survival in TNBC and HER2-positive breast cancers (BCs). We investigated the value of changes in TIL levels and final TIL levels after treatment, by evaluating lymphocyte infiltration before and after NAC in a real-life BC cohort. Patients and methods: We assessed stromal TIL levels in 716 pre- and post-treatment matched paired specimens, according to the guidelines of the international TIL working group. Results: Pre-NAC TIL levels were higher in tumors for which pCR was achieved than in cases of residual disease (33.9% versus 20.3%, p=0.001), in luminal tumors and TNBCs, but not in HER2-positive BCs, (pInteraction =0.001). The association between pre-NAC TIL levels and pCR was non-linear in TNBCs (p=0.005). Mean TIL levels decreased during NAC (pre-NAC TILs: 24.1% versus post-NAC TILs: 13.0%, p Conclusion: The associations of pre, post-NAC TIL levels with response to treatment and DFS differ between BC subtypes and may deviate from linearity. The characterization of immune subpopulations may improve our understanding of the complex interactions between pre- or post-NAC setting, BC subtype, response to treatment and prognosis. Citation Format: Hamy A-S, Bonsang-Kitzis H, De Croze D, Laas E, Darrigues L, Topciu L, Menet E, Vincent-Salomon A, Lerebours F, Pierga J-Y, Brain E, Feron J-G, Benchimol G, Lam G-T, Lae M, Reyal F. Interaction between molecular subtype and stromal immune infiltration dynamics in breast cancer patients treated with neoadjuvant chemotherapy [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-11-01.