Abstract S1-06: Stromal tumor-infiltrating lymphocytes(S-TILs): In the alliance N9831 trial S-TILs are associated with chemotherapy benefit but not associated with trastuzumab benefit

Background: Tumor-infiltrating lymphocytes (TILs) at diagnosis are reported to be prognostic in triple-negative breast cancer (BC). Analysis of a small subset of 209 HER2+ patients (pts) with 49 events concluded that higher levels of S-TILs are associated with increased trastuzumab benefit (Loi, 2014). Here we report the largest study to date evaluating S-TILs and their prognostic and predictive association with clinical outcome in N9831 pts treated with either chemotherapy or chemotherapy plus trastuzumab. Methods: Samples assessed were from primary tumors of pts on N9831 arm A (standard AC→T chemotherapy) and arm C (concurrent chemotherapy with trastuzumab) (Perez, 2011). S-TILs were evaluated on H&E whole tumor slides by a single pathologist with ∼10% of cases read by two pathologists in tandem. The percent of stromal lymphocytic infiltrates (S-TILs) was quantitated in deciles; ≥60% S-TILs was used for the categorical cutoff (Denkert, 2010). The association between S-TILs, treatment (tx) and recurrence-free survival (RFS) was studied and the interaction between S-TILs, trastuzumab benefit and RFS was calculated. Results: 489 pts from arm A (chemo) and 456 pts from arm C (chemo with trastuzumab) were assessed and were similar to pts in the overall trial; all had RFS information and a median follow-up of 4.4yr. Tumors from 54% of pts in arms A and C were HR+; 14% were node-negative. Tumors with high S-TILs were more likely to be hormone receptor-negative (p< 0.0001). In multivariable analyses including nodal status, hormone receptor status, tx arm, tumor size, tumor grade, and age, ≥60% S-TILs was significantly associated with RFS (HR 0.20; 95%CI 0.064–0.65, p=0.007) in arm A but not in arm C (HR 1.1; 95%CI 0.42–2.8, p=0.87); the interaction term of arm and ≥60% S-TILs was significant (p=0.042). Semi-continuous deciles were associated with RFS in arm A (p Arm A (N=489)Arm C (N=456)VariableHR (95% CI)p-valueHR (95% CI)p-valueNodal statusLymph node(-)1.00 (ref) Conclusions: In exploratory analyses from this subset HER2+ population from N9831, S-TILs were associated with RFS in patients treated with chemotherapy alone, and were not shown to be associated with RFS in patients treated with chemotherapy plus trastuzumab. Citation Format: Edith A Perez, Karla V Ballman, S Keith Anderson, E Aubrey Thompson, Sunil S Badve, Helen Bailey, Frederick L Baehner. Stromal tumor-infiltrating lymphocytes(S-TILs): In the alliance N9831 trial S-TILs are associated with chemotherapy benefit but not associated with trastuzumab benefit [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr S1-06.