• Rita Nanda, Minetta C Liu, Christina Yau, Rebecca Shatsky, Lajos Pusztai, Anne Wallace, A Jo Chien, Andres Forero-Torres, Erin Ellis, Heather Han, Amy Clark, Kathy Albain, Judy C Boughey, Nora T Jaskowiak, Anthony Elias, Claudine Isaacs, Kathleen Kemmer, Teresa Helsten, Melanie Majure, Erica Stringer-Reasor, Catherine Parker, Marie C Lee, Tufia Haddad, Ronald N Cohen, Smita Asare, Amy Wilson, Gillian L Hirst, Ruby Singhrao, Katherine Steeg, Adam Asare, Jeffrey B Matthews, Scott Berry, Ashish Sanil, Richard Schwab, W Fraser Symmans, Laura van 't Veer, Douglas Yee, Angela DeMichele, Nola M Hylton, Michelle Melisko, Jane Perlmutter, Hope S Rugo, Donald A Berry, and Laura J Esserman.
• The University of Chicago, Chicago, Illinois.
• JAMA Oncol. 2020 May 1; 6 (5): 676-684.

ImportanceApproximately 25% of patients with early-stage breast cancer who receive (neo)adjuvant chemotherapy experience a recurrence within 5 years. Improvements in therapy are greatly needed.ObjectiveTo determine if pembrolizumab plus neoadjuvant chemotherapy (NACT) in early-stage breast cancer is likely to be successful in a 300-patient, confirmatory randomized phase 3 neoadjuvant clinical trial.Design, Setting, And ParticipantsThe I-SPY2 study is an ongoing open-label, multicenter, adaptively randomized phase 2 platform trial for high-risk, stage II/III breast cancer, evaluating multiple investigational arms in parallel. Standard NACT serves as the common control arm; investigational agent(s) are added to this backbone. Patients with ERBB2 (formerly HER2)-negative breast cancer were eligible for randomization to pembrolizumab between November 2015 and November 2016.InterventionsParticipants were randomized to receive taxane- and anthracycline-based NACT with or without pembrolizumab, followed by definitive surgery.Main Outcomes And MeasuresThe primary end point was pathologic complete response (pCR). Secondary end points were residual cancer burden (RCB) and 3-year event-free and distant recurrence-free survival. Investigational arms graduated when demonstrating an 85% predictive probability of success in a hypothetical confirmatory phase 3 trial.ResultsOf the 250 women included in the final analysis, 181 were randomized to the standard NACT control group (median [range] age, 47 [24.77] years). Sixty-nine women (median [range] age, 50 [27-71] years) were randomized to 4 cycles of pembrolizumab in combination with weekly paclitaxel followed by AC; 40 hormone receptor (HR)-positive and 29 triple-negative. Pembrolizumab graduated in all 3 biomarker signatures studied. Final estimated pCR rates, evaluated in March 2017, were 44% vs 17%, 30% vs 13%, and 60% vs 22% for pembrolizumab vs control in the ERBB2-negative, HR-positive/ERBB2-negative, and triple-negative cohorts, respectively. Pembrolizumab shifted the RCB distribution to a lower disease burden for each cohort evaluated. Adverse events included immune-related endocrinopathies, notably thyroid abnormalities (13.0%) and adrenal insufficiency (8.7%). Achieving a pCR appeared predictive of long-term outcome, where patients with pCR following pembrolizumab plus chemotherapy had high event-free survival rates (93% at 3 years with 2.8 years' median follow-up).Conclusions And RelevanceWhen added to standard neoadjuvant chemotherapy, pembrolizumab more than doubled the estimated pCR rates for both HR-positive/ERBB2-negative and triple-negative breast cancer, indicating that checkpoint blockade in women with early-stage, high-risk, ERBB2-negative breast cancer is highly likely to succeed in a phase 3 trial. Pembrolizumab was the first of 10 agents to graduate in the HR-positive/ERBB2-negative signature.Trial RegistrationClinicalTrials.gov Identifier: NCT01042379.

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