102P Results from a phase II trial of pembrolizumab (P) plus gemcitabine (Gem) in patients (pts) with HER2-negative advanced breast cancer (ABC): GEICAM/2015-04 (PANGEA-Breast) study

Abstract Background This trial is based on a combination strategy with two immunostimulatory agents in the search of synergism that may induce responses with long-term clinical benefit in ABC pts. Safety data from the run-in-phase were published in ESMO IO 2018. Here, we report the results from the phase II part of the study. Methods HER2-negative ABC pts previously treated with anthracyclines and taxanes (unless contraindicated), ≤ 4 chemotherapy lines and/or ≥ 2 hormone therapy lines, and irrespective of PD-L1 status, were eligible. Study treatment consisted of 21-day cycles (cy) of P 200mg on day 1 and Gem 1250mg/m2 on days 1 and 8 until progressive disease (PD) or unacceptable toxicity, whatever occurred first. Primary objective was Objective Response Rate (ORR). Results Thirty-six pts were included in the first stage of a Simon’s design. Recruitment was stopped as only 5 pts presented an objective response (partial) (≥ 7 responses needed to continue recruiting pts). Median age was 52 years (range 31-77), 21 pts had triple negative disease, the majority of pts had an ECOG performance status ≤ 1 (n = 35), visceral involvement (n = 28) and ≥ 2 metastatic locations (n = 27). Median number of prior lines (any therapy) for ABC was 4 (range 0-11). Pts received a median of 4.5 cy of Gem and 4 cy of P (same range for both drugs, 1-24). The median relative dose intensity of P and Gem was 100% and 80%, respectively. Treatment discontinuation due to PD was reported on 29 pts. The ORR was 15.2% (95% confidence interval (CI) 5.1-31.9) and the Clinical Benefit Rate was 17% (95% CI 33.5-69.2); median duration of objective response was 4.3 months (mo) (95% CI 2.3-7.4), median Progression-Free Survival was 3.1 mo (95% CI, 2-4.3), and median Overall Survival was 7.9 mo (95% CI 6.5-10.3). Eight pts were on treatment ≥ 6 mo before PD (2 pts on 11.4 and 16.1 mo). Grade (G) ≥ 3 AEs related to the study treatment were reported on 14 pts (39%), being neutropenia the most common G3 (22.2%) and G4 (5.6%) AE. Conclusion P can be safely combined with Gem, the combination did not meet the efficacy objective in terms of ORR but 22.2% pts were on treatment ≥ 6 mo. Clinical trial identification NCT03025880. Legal entity responsible for the study GEICAM Spanish Breast Cancer Group. Funding MSD. Disclosure J. Cruz: Honoraria (self), Advisory / Consultancy: Glaxo; Honoraria (self), Advisory / Consultancy: AstraZeneca; Honoraria (self), Advisory / Consultancy: Roche; Honoraria (self), Advisory / Consultancy: Novartis; Honoraria (self), Advisory / Consultancy: Pharmamar; Honoraria (self), Advisory / Consultancy: Eisai; Honoraria (self), Advisory / Consultancy: Lilly; Honoraria (self), Advisory / Consultancy: Celgene; Honoraria (self), Advisory / Consultancy: Astellas; Honoraria (self), Advisory / Consultancy: Amgen; Honoraria (self), Advisory / Consultancy: Pfizer. M. Ramos Vazquez: Honoraria (self), Advisory / Consultancy: AstraZeneca; Honoraria (self), Advisory / Consultancy: Roche; Honoraria (self), Advisory / Consultancy: Novartis; Honoraria (self), Advisory / Consultancy: Pfizer. J. Cortes: Honoraria (self), Honoraria (institution), Advisory / Consultancy: Roche; Honoraria (self), Advisory / Consultancy: Celgene; Advisory / Consultancy: Cellestia; Honoraria (institution), Advisory / Consultancy: AstraZeneca; Advisory / Consultancy: Biothera Pharmaceutical; Advisory / Consultancy: Merus; Advisory / Consultancy: Seattle Genetics; Advisory / Consultancy: Daiichi Sankyo; Advisory / Consultancy: Erytech; Advisory / Consultancy: Athenex; Advisory / Consultancy: Polyphor; Honoraria (self), Advisory / Consultancy: Lilly; Honoraria (institution), Advisory / Consultancy: Servier; Honoraria (self), Honoraria (institution), Advisory / Consultancy: MSD; Advisory / Consultancy: GSK; Honoraria (self): Novartis; Honoraria (self), Honoraria (institution): Eisai; Honoraria (self), Honoraria (institution): Pfizer; Honoraria (self): Samsung Bioepis; Honoraria (institution), MedSIR (Stock, patent and intellectual property): Ariad Pharmaceuticals. Baxalta GMBH/Servier Affaires. Bayer Healthcare. Guardanth Health. Piqur Therapeutics. Puma C. Queen Mary University of London. Seagen. All other authors have declared no conflicts of interest.