Long-term outcomes of patients with node-negative (N0), triple-negative breast cancer (TNBC) who did not receive adjuvant chemotherapy according to stromal TILs (sTILs)

548 Background: sTILs are a well-established prognostic and predictive biomarker in patients with operable TNBC receiving pre or postoperative systemic therapy. We1 and others2,3 have also shown that sTILs are prognostic in patients who did not receive adjuvant chemotherapy. Here, we detail the outcomes of systemically untreated patients with N0 TNBC according to sTIL score. We focused on the N0 subset as a group of patients who may be candidates for future prospective therapy de-escalation trials. Methods: From a clinically annotated cohort of 605 patients with centrally confirmed TNBC (ER/PR < 1% and HER2 negative) with long-term outcomes data, we identified 182 patients treated with locoregional therapy only (breast surgery +/- radiation therapy and no chemotherapy). The clinicopathological characteristics of this cohort have previously been published1. In this analysis, we report the 5- and 10-year invasive disease-free survival (iDFS) and overall survival (OS) rates of patients with N0 TNBC according to sTIL levels. IDFS and OS were defined as per the STEEP classification and estimated using the Kaplan–Meier method. Comparisons of the survival distributions between groups were assessed by the log-rank test. sTILs were assessed as a continuous parameter according to the International TIL Working Group guidelines. For comparisons of outcomes between groups, tumors were classified as lymphocyte-predominant TNBC (defined as containing ≥50% sTILs) vs non-lymphocyte-predominant ( < 50% sTILs). Results: Of 182 systemically untreated patients, 149 (82%) were N0 and most (78%) were post-menopausal. T stage distribution was T1: 68%, T2: 28%, T3/4: 4%. Among N0 patients, 31 (21%) had lymphocyte-predominant TNBC, and in this group the 5-year iDFS and OS were 89% (95% CI 76-100) and 96% (95% CI 89-100), while the 10-year iDFS and OS were 89% (95% CI 76-100) and 87% (95% CI 73-100), respectively. In contrast, outcomes for patients with non-lymphocyte predominant TNBC were significantly worse. For this group, 5-year iDFS and OS were 62% (95% CI 53-73) and 78% (95% CI 71-86) while the 10-year iDFS and OS were 45% (95% CI 36-58) and 66% (95% CI 68-76), respectively ( log-rank p = 0.02 for iDFS and log-rank p = 0.03 for OS). Conclusions: sTIL quantification identifies a subset of patients with early-stage N0 TNBC with an exceedingly good prognosis, even in the absence of adjuvant chemotherapy. These data provide support for the evaluation of sTILs as part of prospective investigation of systemic therapy de-escalation strategies in N0 TNBC. References:1Leon-Ferre et al, Breast Cancer Res Treat (2018) 167:89-99 2Park et al, Ann Oncol (2019) 12:1941-1949 3De Jong et al, ESMO 2020