Randomised Phase II Study of Palbociclib Plus Exemestane with GnRH Agonist Versus Capecitabine in Premenopausal Women with Hormone Receptor-Positive HER2-Negative Metastatic Breast Cancer

Background: Endocrine treatment is preferred recommendation by clinical guidelines in premenopausal as well as postmenopausal women with hormone receptor (HR)-positive, HER2-negative metastatic breast cancer (MBC). In real-world clinical practice, however, substantial numbers of patients are treated with chemotherapy in earlier lines The purpose of this phase II study was to compare the clinical antitumor activity and safety of combined therapy with exemestane plus gonadotropin-releasing hormone (GnRH) agonist plus palbociclib with that of capecitabine in premenopausal women with HR-positive, HER2-negative MBC. Methods: This was a prospective, two-arm, randomized, multicenter open-label phase II study. Participants were premenopausal women with breast cancer that had relapsed or progressed during prior tamoxifen. One line of previous chemotherapy for metastatic setting was allowed. Patients were randomized to chemotherapy (capecitabine 1250 mg/m2 twice daily for 2 weeks every 3 weeks) or combination endocrine therapy (exemestane 25 mg/day for 28 days and palbociclib 125 mg/day for 21 days every 4 weeks plus leuprolide). Primary end point was progression-free survival (PFS). Findings: Of 189 patients enrolled between 2015 and 2018 from 14 centers, 184 were randomly assigned to chemotherapy (n=92) or endocrine therapy with palbociclib (n=92). Median age was 44 years (range 28–58). Approximately half the patients (51%) were treatment naive for MBC. During a median 17 months of followup, median PFS was superior for endocrine therapy plus palbociclib than for capecitabine [20·1 vs. 14·4 months, p=0·0469 by log-rank test; hazard ratio 0·659 (95 CI 0·437–0·994)]. Hematological toxicities of ≥ grade 3 were significantly more common with palbociclib than with capecitabine (75·0% vs. 16·3%). Diarrhea (12·0% vs. 38·4%) and hand–foot syndrome (1% vs. 77%) were more common with capecitabine. Interpretation: Exemestane plus palbociclib with ovarian suppression showed clinical benefit in terms of PFS compared with capecitabine in premenopausal patients with HR-positive, HER2-negative MBC. Trial Registration: The ClinicalTrials.gov identifier number was NCT02592746. Funding Statement: This study was supported by Pfizer (exemestane, palbociclib), Shinpoong (capecitabine), Daewoong Korea and Takeda (leuprolide) for study drugs. This work was partly funded by a grant from the Ministry of Health and Welfare, Republic of Korea (HA17C0055) and by the National R&D Program for Cancer Control, Ministry of Health and Welfare, Republic of Korea (1720150). Declaration of Interests: Dr. PARK reports grants and non-financial support from Pfizer, grants and non-financial support from AstraZeneca, grants and non-financial support from Novartis, grants and non-financial support from Merck, grants from Eisai, grants and non-financial support from Roche, outside the submitted work. Dr. Im reports grants from Pfizer, drug supply from Pfizer, Shinpoong, Daewoong, and Dakeda, during the conduct of the study; grants from AstraZeneca and Pfizer, travel expenses for advisory board participation and advisory role for Novartis, advisory role for Hanmi, Pfizer, Eisai, Amgen, Lilly, MediPacto, Roche, outside the submitted work. Dr. Jung reports personal fees from AstraZeneca Korea, personal fees from Roche Korea, outside the submitted work. Dr. Kim reports grants from Ono Pharma Korea Co., Ltd., outside the submitted work. Dr. Ahn reports personal fees and non-financial support from Astrazeneca, Roche, Beringer Ingelheim, Menarini, Pfizer, BMS, ONO, Boryung, grants from Samyang, outside the submitted work. Dr. Lee reports personal fees from AstraZeneca, personal fees from Bayer, personal fees from Eisai, personal fees from Novartis, personal fees from Ono, personal fees from Roche, personal fees from Samsung Bioepis, outside the submitted work. Dr. Kim reports grants from Novarts, grants from Sanofi Genzyme, non-financial support from Dongkook Pharma Co Ltd., outside the submitted work. Dr. Ahn reports personal fees from Amgen, personal fees from Pfizer, personal fees from AstraZeneca, personal fees from Menarini, personal fees from Roche, personal fees from Eisai, personal fees from Boehringer-Ingelheim, personal fees from BMS-Ono, personal fees from MSD, personal fees from Janssen, personal fees from Samsung Bioepis, personal fees from Takeda, outside the submitted work. All other authors declare they have no conflicts of interest. Ethics Approval Statement: The study was conducted in full accordance with the guidelines for Good Clinical Practice and the Declaration of Helsinki, and was approved by the institutional ethics committees of each hospital and the KCSG institutional review board. Written informed consent was obtained from each participant.