460P - Impact of fulvestrant utilization on prognostic outcome among patients with HR+ve/HER2-ve metastatic breast cancer: Results from a real-world dataset

Background

Overall survival (OS) of pts with HR+ve/HER2-ve MBC has improved with the use of CDK4/6i and sequential use of endocrine therapy. The selective estrogen receptor modulator (SERM) Fulvestrant has been shown to work well post progression on aromatase inhibitors (AI) in an endocrine resistant cohort. Clinical trials have shown no difference in progression free survival with the use of an AI or fulvestrant in combination with a CDK4/6i in the first-line setting. The objective of this retrospective analysis was to look at trends in use of and associated prognostic outcome associated with fulvestrant among pts with HR+ve /HER2-ve MBC in the real-world setting.

Methods

We utilized a federated network of de-identified health data representing approximately 107 million pt lives available through the TriNetX Research Network. We identified 47,999 pts with HR+ve /HER2-ve MBC treated with endocrine therapy. OS was computed using the Kaplan Meier product limit method.

Results

Mean age was 60 yrs. 17.5% (n=8390) received fulvestrant at any time of whom 24% received it in the first-line setting. Use of fulvestrant increased from 1.04% in the period 2005-2009 to 9.03% in the period of 2015-2019. 20.6% (n=9,908) received CDK4/6i at any time of whom 39.7% received it in the first-line setting. 2-year OS among pts who did and did not use fulvestrant was 80.3% and 77.5% respectively (HR 0.8, p<0.01). 2-yr OS among pts who did and did not use fulvestrant as first-line therapy was 69.9% and72.6% respectively(HR 1.05, p = 0.41). 2-year OS among pts who did and did not use CDK4/6i was 84.6% and 78.3% (HR 0.64, p < 0.01). 2-yr OS among pts who did and did not receive CDK4/6i as first-line therapy was 78.3% and 73.8% respectively (HR 0.74, p < 0.01). 2-yr OS among pts receiving CDK4/6i with or with out fulvestrant in the first-line setting was 74.7% and 79.1% respectively (HR 1.27, p = 0.06).

Conclusions

Fulvestrant use has increased over time. Real world data indicate OS benefit to use of fulvestrant at some time point in the therapy of pts with HR +ve/HER2-ve MBC. Use of fulvestrant with CDK4/6i in the first-line setting does not improve prognostic outcome compared to use of CDK4/6i + AI in the first-line setting in keeping with the results of clinical trials.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

S. Dawood: Financial Interests, Personal, Advisory Board: Roche, AstraZeneca, Lilly, Merk, Gilead; Financial Interests, Personal, Invited Speaker: Roche, MSD, BMS, Pfizer, Lilly, AstraZeneca, caris; Financial Interests, Institutional, Research Grant: MSD, Amgen; Non-Financial Interests, Member: ASCO. All other authors have declared no conflicts of interest.