258 Scientific correlatives from LCCC 1525: a phase II study of a priming dose of cyclophosphamide prior to pembrolizumab to treat metastatic triple negative breast cancer

• Published in: Journal for immunotherapy of cancer 2020-11, Vol.8 (Suppl 3), p.A281-A282
• Main Authors: Woodcock, Mark, Anders, Carey, Swearingen, Amanda Van, Moore, Dominic, Sambade, Maria, Cuaboy, Luz, Garrett, Amy, McKinnon, Karen, Cowens, Kristen, Bortone, Dante, Calhoun, Benjamin, Carey, Lisa, Dees, Claire, Jolly, Trevor, Muss, Hyman, Reeder-Hayes, Katherine, Kaltman, Rebecca, Jankowitz, Rachel, Gudena, Vinay, Olajide, Oludamilola, Perou, Charles, Vincent, Benjamin, Serody, Jonathan
• Format: Article
• Language: English
• Subjects: Apoptosis; Breast cancer; Cancer therapies; Gene expression; Immunotherapy; Metastasis; Monoclonal antibodies; Targeted cancer therapy
• ISSN: 2051-1426
• DOI: 10.1136/jitc-2020-SITC2020.0258

BackgroundIn metastatic triple negative breast cancer (mTNBC), median progression-free survival (PFS) with chemotherapy alone is approximately 2–4 months1 and improvements with single agent checkpoint inhibitors (CI) are limited by modest response rates. Murine breast cancer models have demonstrated a role for intratumoral regulatory T cells (Tregs) in modulating response to CIs.2 A phase II clinical trial was conducted to test the hypothesis that a single, priming dose of cyclophosphamide prior to pembrolizumab would improve PFS in mTNBC. Here we present the correlative genomic and immunologic analyses from this study.MethodsThis trial (https://clinicaltrials.gov/ct2/show/NCT02768701) recruited 40 patients with largely pretreated mTNBC. Response was defined as >30% decrease in imaging-assessed disease burden. Clinical benefit was defined as treatment response or stable disease. Tumor specimens were collected prior to enrollment, and peripheral blood mononuclear cell (PBMC) samples taken prior to cyclophosphamide and before each cycle of pembrolizumab. RNA sequencing was performed on tumor samples for gene expression and immune repertoire reconstruction. Targeted sequencing of the T-cell beta chain, IG kappa, lambda and heavy chain (TRB, IGK, IGL, and IGH, respectively) on PBMCs captured the peripheral immune repertoire. Whole exome sequencing was performed on tumor samples with PBMCs serving as a matched normal.ResultsOf 40 patients enrolled, 31 patients had tumor RNA-seq and at least 15 had matched PBMC-derived immune chains capturing both pre and post treatment. When preliminary RNA-seq samples (n=22) revealed upregulation in B-cell receptor pathways and related gene signatures (figure 1), we updated our planned analysis to exclude tumor specimens collected from lymph nodes. In our final analysis, response to therapy (4 of 25, 16%) was associated in tumor RNA-Seq with gene pathways involving programmed cell death and MAPK activation, while non-responding tumors were enriched in G-protein signaling and inhibition of insulin secretion (figure 2a,b, table 1). Immune gene signatures related to NK cells and B-cell activation, signaling and interaction with T follicular helper cells,3–7 were associated with response (figure 2g). Pre-treatment immune repertoire measures demonstrated a significant association between increased peripheral IGH abundance and richness, and both future clinical benefit and response to therapy (figure 3a-d).Abstract 258 Figure 1Gene