422P - UK real-world data (RWD) of cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) use in metastatic breast cancer (MBC)

Background

Many studies support the use of CDK4/6i in MBC with aromatase inhibitors or fulvestrant. We assessed the efficacy and tolerability of CDK4/6i using RWD.

Methods

RWD was collected retrospectively from 5 UK centres. Patients with a diagnosis of ER+/HER2- MBC treated with a CDK4/6i between Apr 17 and Nov 22 were included. We used Kaplan-Meier statistical analysis to calculate follow-up time, progression free survival (PFS) and overall survival (OS).

Results

665 patients were included (median age 66 (range 23-92)). 243 (36.5%) were documented as pre- and 343 (51.6%) as post-menopausal. 543 (81.7%) had 1^st-line CDK4/6i and 122 (18.3%) had ≥ 2^nd-line treatment. 536 (80.6%) received Palbociclib (P), 85 (12.8%) Abemaciclib (A) and 44 (6.6%) Ribociclib (R). The median follow-up time was 28 months (range 0-76; IQR 18-41). 1^st-line PFS was P - 31 months (25-35), A - 16 months (9-NR) and R - 44 months (21-NR). ≥ 2^nd-line PFS was P - 12 months (10-29), A - 15 months (11-30) and R - 15.5 months (10-NR). OS data is immature. Overall, 527 (79.2%) patients suffered any grade toxicity (P - 414 (77.2%), A - 72 (84.7%) and R - 41 (93.1%)) and 248 (37.2%) ≥Grade 3 (≥G3) (P - 203 (37.9%), A - 22 (25.9%) and R - 23 (52.3%)). The table outlines the most common toxicities by drug and grade. 366 (55%) patients had 1 dose reduction (DR): P - 290 (54.1%), A - 50 (58.8%) and R - 26 (59%). The median time to DR was 2 months (1-63), with no significant difference noticed between CDK4/6i. 113 (17%) patients had >1 DR: P - 96 (17.9%), A - 6 (13.6%) and R - 11 (12.9%). Table: 422P

Conclusions

This large, RWD-set demonstrates PFS comparable to that of published trial data, but outcomes for A and R are impacted by small numbers and short follow up. ≥G3 toxicity was highest for P and R compared to A and lower than previously described, though DR rates were similar, suggesting significant side-effects were experienced. As their use increases and extends to the adjuvant setting, complete and mature RWD examining CDK4/6i toxicity, PFS and OS is required, especially for A and R.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

S. Spensley: Financial Interests, Personal, Speaker, Consultant, Advisor, Meetings and Advisory Boards - reimbursed: Lilly, Roche, Pfizer. T. Robinson: Financial Interests, Personal, Sponsor/Funding: Amgen, Daiichi Sankyo, MSD. All other authors have declared no conflicts of interest.