448P - Real-world experience with CDK4/6 inhibitors for HR+/HER2-metastatic breast cancer (MBC)

Background

Metastatic hormone receptor-positive (HR+)/human epidermal growth factor receptor-2-negative (HER2-) breast cancer remains a significant cause of cancer-related mortality. First-line treatment with endocrine therapy (ET) with a cyclin-dependent kinases 4 and 6 inhibitor (CDK4/6i) has become the standard of care. Data on populations that have been treated in the real-world setting may provide an insight into changes of patient characteristics and prognosis over time.

Methods

Retrospective data of patients (pts) who received CDK4/6i with ET between 2017 and 2022 at University Hospitals of Leicester NHS Trust were analysed. Patient characteristics, efficacy and toxicity outcomes were examined. Kaplan-Meier survival curves were determined using SPSS program.

Results

In all, 235 pts who were on ET in combination with Palbociclib 51% (n=119), Ribociclib 41% (n=97) and Abemaciclib 8% (n=19) were included. The median age was 62 years (33-90). De novo MBC accounted for 33% (n=78) of pts. Most (n=180, 70%) were post-menopausal. The majority 74% (n=175) had visceral disease (lung, liver, peritoneum) vs 26% (n=60) with bone-only disease. The CDK4/6i was discontinued in 48% (n=113) due to disease progression. Over half (n=135, 57%) required at least one dose reduction (DR). The most common reason for DR was neutropenia. Sixty (26%) pts remain on treatment at the time of analysis. Thirteen pts had CDK4/6i switched within 3 months of starting treatment due to toxicities. Median duration on Palbociclib (P), Ribociclbib (R), and Abemaciclib (A) was 20 months; 95% CI= 16.4-23.6, 18; 95% CI= 12.6-23.4 and 8; 95% CI= 0.7-15.3 months respectively. Median PFS between different CDK4/6i were P (24 months; 95% CI= 19.5-28.7), R (27 months; 95% CI= 20.5-33.3) and A (13 months; 95% CI= 6.8-18.9), p=0.22. The difference in median OS was statistically significant (p=0.004) between CDK4/6i; P (54 months; 95% CI= 42.4-58.8), R (46 months; 95% CI= 32.8-60.1) and A (26 months; 95% CI= 4.2-47.8).

Conclusions

CDK4/6i is safe and effective in this population with extensive burden of disease. Dose reduction did not appear to have an impact on efficacy. Survival outcomes observed were similar to randomised phase 3 clinical trials.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.