36O - ¹⁸F-fluoroestradiol (¹⁸F-FES) PET/CT guided first-line treatment for HR+/HER2- metastatic breast cancer patients: Experience from real-world

Background

Although cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) plus endocrine therapy (ET) is the standard first-line treatment option for hormone receptor (HR) positive and human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer (MBC) patients, a minority of patients fail to benefit from this therapy probably because of estrogen receptor (ER) heterogeneity between lesions. ¹⁸F-fluoroestradiol (FES) positron emission tomography (PET)/computed tomography (CT) is recognized as a potent tool for assessing ER expression in patients with HR+/HER2- MBC on a comprehensive, whole-body level. However, whether ER status screened by FES could identify patients who benefit more from CDK4/6i plus ET or chemotherapy (CT) than unscreened controls remains unknown.

Methods

The medical records of patients diagnosed with HR+/HER2- MBC from 2020 to 2023 in Fudan University Shanghai Cancer Center were retrospectively evaluated. Patients screened or unscreened by FES-PET/CT before first-line CDK4/6i plus ET or CT were included in this study.

Results

A total of 432 patients were included in the study. 155 (35.9%) and 277 (64.1%) patients were screened or unscreened by FES-PET/CT before first-line treatment. 111 patients with all-ER positive metastatic lesions and 17 patients with ER heterogeneity received CDK4/6i plus ET. 21 patients with all-ER negative metastatic lesions and 6 patients with ER heterogeneity received CT. As for the unscreened group, 202 received CDK4/6i plus ET and 75 received CT. In CDK4/6 plus ET cohort, FES-screened group showed a significantly prolonged progression-free survival (PFS) compared with unscreened group (mPFS 32.4 months versus 18.0 months, Hazard Ratio = 0.48; 95% CI, 0.34 to 0.69; P < 0.0001). And CT cohort showed superior PFS for screened patients as well (mPFS 11.35 months versus 8.91 months, Hazard Ratio = 0.56; 95% CI, 0.33 to 0.97; P = 0.035).

Conclusions

HR+/HER2- MBC patients with FES-guided initial treatment showed significantly better efficacy than those who had not been assessed by FES-PET/CT in real world. This study highlights the crucial role of FES assessment in evaluating ER expression in patients prior to administering first-line treatment.

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.