Single center observational study of the efficacy of chemotherapy in breast cancer patients treated before and after the widespread use age of CD4/6 inhibitors: Is there evidence that chemotherapy response is impacted by prior use of CD4/6 inhibitors?

Abstract

e13019 Background: Recently CD4/6 inhibitors have radically changed treatment pathways, leading to a deferment of chemotherapy for advanced disease. Patients still relapse following this treatment; we wish to share our experience of chemotherapy both before and after this change and explore whether there is a change in efficacy. In England CD4/6 inhibitors are prescribed according to the guidelines set out by NHS England (NICE), and are generally utilised in the first line setting unless there is visceral crisis. Methods: This is a retrospective double cohort observational single centre study comparing the efficacy of a chemotherapy regimen (vinorelbine and capecitabine vin cap) before and after the incorporation of CD4/6 inhibitors into breast cancer treatment (Jan 2017- Nov 20). The doublet chemotherapy is widely used at our centre providing a well tolerated and effective alternative to intravenous treatments such as taxanes or single agent capecitabine. Data was collected contemporaneously using e prescribing software and audited retrospectively Results: In the audit period n=19 treated with cap, n= 97 with vin cap, n= 24 treated with CD4/6, (of whom 5 relapsed). 5 patients received abemaciclib first line, as initial therapy, all G3, stage 11A or above, median number of cycles 4.2, I received ribociclib, G2, stage 111A, 7 cycles and 17 received palbociclib, 10 first line, 4 following 1 course chemo, 2 after 2 courses and 1 and after 3 courses, 30% G3 and 70% G2, mean number of cycles 11.06. Patients who received first line cap progressed after a median of 3.5 cycles, with a range of 0-22 months (RR= 47%), for cape vin a median of 8.6, a range of 0-60 months (RR=77%), post CD4/6 mean of 8, median of 9, a range of 0-17 (RR=80%). Conclusions: Those post CD4/6 requiring chemo relapsed far short of the median TTP of around 26months and may have specific characteristics predicting poor response to CD4/6. Despite small numbers salvage chemotherapy remains effective with similar responses. First line vin cap is more efficacious and better tolerated than Cap.[Table: see text]