417P - New insights into second-line (2L) choices after CDK4/6 inhibitors (CDK4/6i) in hormone receptor-positive (HR+)/ human epidermal growth factor 2-negative (HER2-) metastatic breast cancer (MBC) patients (pts): Preliminary results of the HERMIONE-13 study

Background

CDK4/6i with endocrine therapy (ET) still represents the best 1^st-line (1L) choice for HR+/HER2- MBC pts. At progression, the optimal subsequent strategy remains an open question. The HERMIONE-13 study aims to describe the efficacy of 2L choices in terms of Progression Free Survival (PFS) and Clinical Benefit Rate (CBR), in HR+/HER2- MBC pts relapsed after CDK 4/6i + ET.

Methods

HERMIONE-13 is a retrospective and prospective multicentric observational trial conducted in 15 Centers in Italy. Data of pts with at least one disease’ revaluation during 2L therapy are being collected from January 2016 until January 2024. Here we present the first data of pts enrolled until December 2020.

Results

Among 114 pts enrolled, 16 (14%) were primary endocrine resistant, 70 (61.4%) had visceral metastases and 64 (56%) have received Palbociclib. Median 1L PFS (mPFS) was 11 months (mo) (interquartile range (IQR): 5-18). The 2L preferred choice was a chemotherapy (CHT)-based regimen (69.3%), with a predominance of single agent Capecitabine (22,2%); ET + target therapy (TT) was chosen in 16.7% of pts and ET monotherapy in 14%. An ET-based treatment was more frequently chosen for pts with a PFS≥6 mo to previous CDK4/6i (35.4%), with respect to those with a PFS<6mo (13.3%) (P=0.024). A significant improvement in CBR, defined as absence of disease progression at 1^st reassessment, was observed with CHT versus ET (20%, P=0.047). Among CHT treatments, a metronomic schedule of oral Capecitabine +/- Vinorelbine +/-Cyclophosphamide was used in 22.8% of pts, with a mPFS of 6 mo. Table: 417P

Conclusions

In Italy, the preferred 2L treatment after CDK 4/6i remains CHT, especially with single-agent or metronomic schedule. mPFSs of 2L choices are very similar each other, around 6 mo. Further efforts to understand the type of resistance to CDK4/6i are warranted to better select 2L therapy.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

University of Milan Bicocca.

Funding

Has not received any funding.

Disclosure

O. Garrone: Financial Interests, Advisory Board: Eisai, MSD, Daiichi Sankyo, Gilead; Financial Interests, Other, Honoraria: Novartis, Pfizer, Lilly. M. Mazzotta: Financial Interests, Advisory Board: Roche, AstraZeneca. P. Vici: Financial Interests, Personal, Advisory Board: Novartis, Eisai, Pfizer, Lilly; Financial Interests, Institutional, Local PI, multicentric trial (Persevera): Roche; Financial Interests, Institutional, Local PI, multicentric study (LIDERA): Roche; Financial Interests, Institutional, Local PI, EPIK B2: Novartis. All other authors have declared no conflicts of interest.