214P Comparing ribociclib versus palbociclib as a second-line treatment in combination with fulvestrant in metastatic breast cancer: A randomised clinical trial

CDKIs are approved for treatment of ER+, HER2- advanced breast cancer in the 1st line and subsequent lines in combination with AIs or fulvestrant. Studies showed they extend PFS and OS benefit. The efficacy and toxicity of Palbociclib and Ribociclib were not directly compared and were not assessed in the Egyptian population. This is a phase III randomised open label clinical trial that took place at the oncology centre Mansoura university, Egypt. Patients with ER+ HER2- metastatic breast cancer who prgressed on ET were randomised to receive either palbociclib or ribociclib with the combination of fulvestrant. premenopausal women received the LHRH agonist. Toxicity was assessed and graded using CTCAE v5.0. Patients were evaluated clinically for response and toxicity monthly and radiologically by CT/ 3 months. Both arms had similar baseline characteristics. There was no statistically significant difference in the CBR (58.6% for both arms at 6 months and 13.8% in the palbociclib VS 17.2% in the ribociclib arm at 12 months) or in PFS(13.67 months with palbociclib and 12.69 months with ribociclib). PFS was similar in premenopausal patients in both arms, postmenopausal patients had better survival in the palbociclib arm. Multivariate analysis revealed that postmenopausal 2.85 more likely to survive than premenopausal patients. Also patients with ECOG performance status 2 and 3 are 0.13 and 0.39 less likely to survive compared to patients with PS 1. Dose reduction increased the likelihood of survival 3.36 compared with no dose reduction. Regarding common toxicities there was no statistically significant difference between the two arms. 12% of palbociclib patients and 15.5% of the ribociclib patients had dose reduction due to toxicity. After progression on CDK Is, 12% of the patients in the palbociclib arm received chemotherapy and 24% received everolimus while in the ribociclib arm 13.7% and 34.4% received chemotherapy and everolimus respectively. By the end of follow-up 43.1% in the palbociclib arm and 46.5% of the ribociclib arm progressed, commonly with visceral disease. Both Ribociclib and palbociclib have similar clinical benefit rate, PFS and toxicity profile.