Abstract PO3-13-06: TILs are an independent prognostic factor in early-stage TNBC patients achieving pathologic complete response after neoadjuvant chemotherapy

Abstract Introduction: In patients with triple negative breast cancer (TNBC) the achievement of pathological complete response (pCR) after neoadjuvant chemotherapy (NACT) is associated with better long-term clinical outcomes. However, the attainment of pCR does not guarantee cure, since ~ 10% of patients undergo disease relapse. Higher levels of tumor infiltrating lymphocytes (TILs) are associated with better prognosis in TNBC patients undergoing upfront surgery and in patients with residual disease after NACT. However, the prognostic role of TILs among TNBC patients undergoing pCR during NACT has not been investigated so far. Methods: We included 134 TNBC patients (ER cutoff 10%) who achieved pCR after NACT. These cases were identified from a cohort of 348 TNBC patients who received NACT at Istituto Oncologico Veneto (Padova) and Istituto Nazionale Tumori (Milano) from April 2004 to April 2021. TILs were quantified in pre-NACT tumor biopsy according to International guidelines. We assessed the association between TILs and relapse-free survival (RFS) or overall survival (OS). Results: Main patients characteristics were: median age 48 years; ductal histotype 92.8%; histologic grade 3 95.2%; stage I 9.7%, stage II 71.6%, stage III 18.7%. Almost all patients received anthracyclines (98.5%) and taxanes (99.3%) as part of NACT for a median number of 4 cycles each; 55.2% of patients received carboplatin. At a median FU of 4.6 years, the 5-yr RFS and OS rates were 90.4% and 94.4%, respectively. As a continuous variable (1% increment), TILs were independently associated with better RFS and OS after adjusting for patient age and tumor stage: HR 0.90 (95%CI 0.83-0.98), p=0.015 and HR 0.89 (95%CI 0.80-1.00), p=0.041, respectively. The best prognostic TILs cut-off in this cohort was 20%. Patients with TILs20% showed a 100% 5-yr RFS rate (0/63 events) vs 82.6% (12/71 events) for patients with TILs 20% (log-rank p 0.001). OS rates at 5 years were 100% and 90.1% for high vs low TILs (log-rank p=0.007). Conclusions: This is the first demonstration of an independent prognostic role of baseline TILs in TNBC patients achieving pCR after NACT. Baseline TILs may discriminate patients who are cured after achieving pCR from patients at risk of disease relapse despite the achievement of pCR. These latter may be candidate to treatment escalation in the context of clinical trials. Our work provides relevant data in the ongoing debate on the role of adjuvant therapy (primarily pembrolizumab) following pCR. Citation Format: Maria Vittoria Dieci, Claudio Vernieri, Davide Massa, Lorenzo Nicolè, Gaia Griguolo, Federica Miglietta, Andrea Vingiani, Riccardo Lobefaro, Fabio Girardi, Grazia Vernaci, Tommaso Giarratano, Carlo Alberto Giorgi, Giancarlo Pruneri, Matteo Fassan, Filippo De Braud, Valentina Guarneri. TILs are an independent prognostic factor in early-stage TNBC patients achieving pathologic complete response after neoadjuvant chemotherapy abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-13-06.