Abstract P3-16-01: Immune characterization of inflammatory breast cancer and correlation to pathological complete response

Abstract

Abstract Background: Treatment of inflammatory breast cancer (IBC) includes neoadjuvant chemotherapy (NAC) followed by mastectomy and radiation. Responses are limited however with low pathological complete response (pCR) rates and poor survival. Recent RNA expression studies suggest that activated T cell signaling pathways and immunomodulatory markers such as PD-L1 are associated with a higher pCR rate in IBC; however comprehensive studies of tumor infiltrating lymphocytes (TIL) and protein expression of immunomodulatory molecules are lacking. There is a critical need therefore to study molecular and immune determinants of therapeutic response in IBC, with the goal of identifying biomarkers and actionable strategies to improve treatment outcomes. Methods: Baseline core biopsies from 36 IBC patients, 22 with stage III and 14 with stage IV disease were evaluated. Of these, 21 stage III and 10 stage IV patients underwent mastectomy following NAC, the latter for palliative purposes. Tumor subtype distribution was 14 patients with HER2-/HR-, 6 with HER2+/HR-, 11 with HER2-/HR+, and 5 with HER2+/HR+ disease. TIL infiltration in the tumor stroma was quantified on H&E slides based on consensus guidelines as well as by immunohistochemistry (IHC) staining for CD8. PD-L1 expression in the TIL and invasive tumor was evaluated by IHC in tumors with >1%TIL. Results: Stromal TIL were found in the invasive tumor on pretreatment biopsies in 26 (72%) patients, with TIL percentages ranging from 1% to 60% (mean=11.6; sd=13.8); of note, 1 patient biopsy sample only had tumor emboli on the tissue block and therefore was not evaluable. Higher TIL infiltrate was noted in stage III versus stage IV disease (mean TIL 11.6% versus 3.5%, p=0.028). Mean TIL infiltrate was 11.5% in HER2-/HR-, 10.0% in HER2+/HR-, 10.4% in HER2+/HR+, and 3.6% in HER2-/HR+ tumors (p=NS). At mastectomy, 7/21 stage III patients and 1/10 stage IV patients achieved a pCR. Mean TIL was 13.4% in the pCR group versus 8.2% in the non-pCR group (p=0.37) CD8 and PD-L1 staining was performed on samples with >1%TIL (n=15, of which 14 samples were available for additional staining). An average of 42% of TIL stained positive for CD8 (range 10-80%). There was no significant relationship between %CD8 and pCR, stage, or receptor status. None of these 14 patients demonstrated membranous PD-L1 positivity but all had focal weak cytoplasmic staining in the lymphocytes. Conclusions: Differences exist in the presence of stromal TIL in distinct groups within IBC (stage III versus stage IV disease and across histologic subtypes) and may contribute to differential responses to therapy. When comparing these results to published non-IBC literature (FinHER trial), our IBC patient cohort had lower TIL infiltrate in several histologic subtypes (HER2-/HR- 11.5% vs 25%, p=0.015), HER2+/HR-(10% vs 20%, p=0.10), and HER-/HR+ disease (3.6 vs 7.5%, p=0.01); TIL was comparable for HER2+/HR+ disease. Additional studies are underway (including multiplex analysis of myeloid and lymphoid markers, T cell receptor sequencing, and molecular profiling) in pre-treatment and surgical samples to better understand mechanisms of treatment response and resistance. Citation Format: Reddy SM, Wargo JA, Reuben A, Reuben J, Woodward W, Ueno N, Mittendorf EA, Krishnamurthy S. Immune characterization of inflammatory breast cancer and correlation to pathological complete response [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P3-16-01.