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2019 ASCO Annual Meeting!

Session: Developmental Immunotherapy and Tumor Immunobiology

Type: Poster Session

Time: Saturday June 1, 8:00 AM to 11:00 AM

Location: Hall A

An open label, multicenter phase II study combining imprime PGG (PGG) with pembrolizumab (P) in previously treated metastatic triple-negative breast cancer (mTNBC).

Conduct of Clinical Research

Developmental Immunotherapy and Tumor Immunobiology

2019 ASCO Annual Meeting

Abstract No:

Poster Board Number:
Poster Session (Board #194)

J Clin Oncol 37, 2019 (suppl; abstr 2550)

Author(s): Steven O'Day, Virginia F. Borges, Bartosz Chmielowski, Ruta D. Rao, Maysa M. Abu-Khalaf, Alison Stopeck, Petros Nikolinakos, Melinda L. Telli, Bin Xie, Montaser F. Shaheen, Paulette Mattson, Michele Anne Gargano, Joanna Cox, Vassiliki Karantza, Michael Jon Chisamore, Bruno Osterwalder, Nandita Bose, Mark T. Uhlik, Jeremy Graff; John Wayne Cancer Institute, Santa Monica, CA; University of Colorado Comprehensive Cancer Center, Aurora, CO; Division of Hematology-Oncology, David Geffen School of Medicine at UCLA, Los Angeles, CA; Rush University Medical Center, Chicago, IL; Sidney Kimmel Cancer Center at Jefferson, Philadelphia, PA; Stony Brook Cancer Center, Stony Brook, NY; University Cancer and Blood Center, LLC, Athens, GA; Stanford University School of Medicine, Stanford, CA; Swedish Cancer Institute, Issaquah, WA; University of Arizona Cancer Center, Tucson, AZ; Biothera Pharmaceuticals, Inc., Eagan, MN; Biothera, Eagan, MN; Merck & Co., Inc., Kenilworth, NJ; Merck & Co., Inc., Rahway, NJ; Merck KGaA, Darmstadt, Germany

Abstract Disclosures


Background: Checkpoint inhibitor (CPI) monotherapy shows limited clinical response in previously treated mTNBC patients (pts) (Table). Agents are needed that extend this benefit to more mTNBC pts. PGG is a novel, IV administered PAMP that, in pts with 20ug/ml anti-beta glucan antibody (ABA+), activates innate immune cells. Preclinically, PGG reprograms myeloid cells to repolarize the immunosuppressive tumor microenvironment & enhance antigen presentation, driving T cell activation- the mechanistic basis to explore PGG + P in mTNBC patients. Methods: 44 mTNBC pts ( 1 line of chemotherapy [Tx] for metastatic disease, ABA) received PGG (4 mpk IV weekly) + P (200 mg IV q3w) until PD or intolerable toxicity. 1° endpoints were ORR by RECIST v1.1 & safety. 2° endpoints included OS & DCR. CT scans (q6 wks) were reviewed locally. Tumor biopsies (pre & 6 wks on Tx) & blood samples were assessed for PGG-mediated immune activation. Results: Table shows IMPRIME 1 clinical response data (Keynote086, PCD4989g shown for context). Confirmed response was also evident in pts with liver or visceral metastases, high LDH. 10 IMPRIME 1 pts were originally ER/PR+, received hormonal Tx and progressed to TNBC. Of these, 5 are confirmed PR, 4 SD (3 still on Tx), 1 PD. No unexpected safety signals were observed. Conclusions: These are the first clinical data to suggest that PGG provides added clinical benefit for pts with previously treated mTNBC and support further development of PGG + P for mTNBC. Clinical trial information: NCT02981303

% (N= 44)
Keynote 086a
% (N=170)
% (N=94)
ORR13.6 (6)5.36.4
SD40.9 (18)1813
PD40.9 (18)60.664
DCR - CR+PR+SD ≥ 24wks22.7 (10)7.610
Median OS in months13.79.07.3
% OS 6/ 12 months83.0/ 65.569.7/ 39.860/ 37

aAdams 2018, bEmens 2019 In peripheral blood, Tx increased activated (HLA-DR/CD86+) monocyte & dendritic cell subsets as well as CD8 T cells (Ki67/HLA-DR/PD1+), particularly in responsive pts. All tumor biopsy pairs showed heavy infiltration by activated myeloid (PDL1+) and CD8 T cells (Ki67/granzyme B+) after Tx. These data support the mechanistic basis for PGG-based combination with P. NCT02981303 sponsored by Biothera in collaboration with Merck & Co., Inc.

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