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EP208 Tumor infiltrating lymphocytes – marker of therapy response in breast cancer

Introduction/Background Tumor infiltrating lymphocytes (TILs) are mononuclear immune cells (mainly CD8+ cytotoxic T lymphocytes), infiltrating tumor and surrounding tissues. High levels of TILs might be associated with better response to chemotherapy and better overall survival and disease free survival in patients with particular subtypes of breast cancer. Methodology Our study comprised of an analysis of 45 consecutive patients with HER2 positive or triple negative breast cancer (TNBC), treated in the neoadjuvant setting with chemotherapy (antracycline-based chemotherapy and taxanes) and Trastuzumab (if HER2 positive). TILS were assessed using HE staining on core biopsies (cut-off 5%), in chemo-naive patients. Postoperative, pathological complete response (pCR) was assessed for all specimens. Results The median age of our population was 58 years old. 96% of cases were invasive ductal carcinoma NST, 3% - invasive lobular carcinoma and 1% - mixt type. Regarding the molecular subtype, 63.6% were HER2 amplified and 37.4% were TNBC. In our population, 60% of patients had pCR. Of the pCR patients, 81% had TILs positive, while 67% of non-pCR patients had TILs positive. In the HER2 positive subpopulation, 81% of the TILs positive and 40% of the TILs negative had pCR, while in the TNBC subpopulation 55.5% of the TILs positive had pCR. Level of TILs expression did not show a significant difference between pCR and non-pCR groups (39% vs 38%), only the presence or absence of TILs. Conclusion In conclusion, increasing pCR in HER2 positive and triple negative breast cancer correlated with the presence, but not with the levels of TILs. TILs presence on biopsy specimen could be used as a marker of therapy response and insertion of a radiopaque marker in tumor bed in patients with increased likelihood of pCR should be considered, to make breast conserving surgery possible. TILs definite role in breast cancer should be established in future trials. Disclosure Nothing to disclose.