On June 3, 2019 SELLAS Life Sciences Group, Inc. (Nasdaq: SLS) ("SELLAS" or the "Company"), a clinical-stage biopharmaceutical company focused on the development of novel cancer immunotherapies for a broad range of cancer indications, reported results from a preplanned analysis of immunologic responses in the cohort of patients with triple negative breast cancer (TNBC) from the prospective, randomized, single-blinded, controlled Phase 2b independent investigator-sponsored clinical trial of nelipepimut-S (NPS) +/- trastuzumab (Herceptin) targeting HER2 low-expressing breast cancer patients (Press release, Sellas Life Sciences, JUN 3, 2019, View Source [SID1234536812]). This analysis was presented on June 2, 2019 at the 55th Annual Meeting of the American Society of Clinical Oncology (ASCO) (Free ASCO Whitepaper) in Chicago, IL.
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"Effective adjuvant/maintenance therapy strategies are urgently needed to prevent recurrence or to prolong remission in patients with TNBC after successful frontline standard therapy for early-stage disease. In this setting, immune-directed therapy with NPS, a peptide vaccine targeting HER2, a protein expressed at low levels in TNBC, along with trastuzumab, led to high rates of antigen-specific immunization by both ex vivo and in vivo validated measures, corroborating the immunobiological synergy between these two agents," said Elizabeth A. Mittendorf, MD, PhD, Rob and Karen Hale Distinguished Chair in Surgical Oncology, Director of Research, Breast Surgical Oncology Brigham and Women’s Hospital, Director, Breast Immuno-Oncology Program Dana-Farber/Brigham and Women’s Cancer Center, and the Principal Investigator of the Phase 2b study.
"These ex vivo and in vivo results in TNBC patients, particularly the newly discovered correlation between mounting an immune response and remaining clinically relapse-free over time, provide a solid mechanistic rationale for the previously observed clinically meaningful and statistically significant prolongation in disease-free survival (DFS), and the significant decrease in the frequency of relapses identified by standard clinical follow-up, in favor of NPS plus trastuzumab," said Angelos M. Stergiou, MD, ScD h.c., President and Chief Executive Officer of SELLAS.
"As we continue discussions with potential partners and the U.S. Food and Drug Administration (FDA) on this promising program, we remain excited with these data demonstrated in the TNBC population," added Dr. Stergiou.
The Phase 2b study enrolled patients with HER2-low expressing breast cancer who remained clinically disease-free after completion of frontline standard of care therapy. Patients were selected to harbor node-positive disease and/or TNBC, as well as expressing human leukocyte antigen (HLA) types indicated for NPS administration (A2, A3, A24/26; pertinent to approx. 85% of the global population). Patients were randomized to placebo with granulocyte-macrophage colony-stimulating factor (GM-CSF) (n=139) or NPS with GM-CSF (n=136), while they all received trastuzumab every 3 weeks for one year. The Company previously reported results of the final analysis of efficacy and safety outcomes in the cohort of patients whose tumors did not express hormone receptors, TNBC (n=97). DFS of patients treated with NPS plus trastuzumab (n=53) was 92.6% compared to 70.2% for those treated with trastuzumab alone (n=44) and represented a clinically meaningful and a statistically significant improvement with the combination therapy, p=0.01. This was associated with a statistically significant reduction by 71.9% (p=0.01) in the frequency of clinically detected recurrences in favor of the combination in the TNBC cohort.
Ninety-one of the 97 TNBC patients in this clinical study were analyzed for immune responses (IR) at five timepoints, 51 of whom received the combination therapy. IR were evaluated ex vivo by clonal expansion of antigen NPS-specific cytotoxic T-lymphocytes (CTL) by dextramer-staining/flow cytometry at predefined time points over three years. In vivo IR were assessed by cutaneous delayed type hypersensitivity (DTH) reactions periodically, by measuring the diameter of skin induration (in mm) post intradermal NPS treatment.
NPS plus trastuzumab-treated TNBC patients exhibited increases in CTL frequencies compared with baseline by 1.1-, 1.73-, and 2.86-fold at 18, 24 and 30 months, respectively. The mean CTL frequencies in these patients increased from 29±0.1 per 10-4 at baseline to 112±2.6% at 30 months, a 2.86-fold difference that was highly clinically indicative (p = 0.058), as compared with patients receiving trastuzumab only, whereby CTL frequencies were 20±0.1 per 10-4 at baseline compared with 52±1.6 per 10-4 at 30 months, a 1.6-fold non-significant difference (p=0.70). Three patients in the combination arm recurred (5.9%) as compared with 12 (30%) in the trastuzumab-alone arm. TNBC patients treated with NPS plus trastuzumab whose disease recurred did not mount an IR by ex vivo assessment (absolute CTL frequency change) or by in vivo DTH (no change in skin induration), while non-recurrent patients mounted both vigorous NPS-specific clonal CTL expansion and enhanced in vivo DTH.