Randomized phase II trial of venetoclax + fulvestrant versus fulvestrant in estrogen receptor+, HER2– locally advanced or metastatic breast cancer following recurrence or progression during or after a CDK4/6 inhibitor: VERONICA.

Abstract

TPS1108 Background: CDK4/6 inhibitors (CDK4/6is) administered with endocrine therapy have demonstrated improvements in progression-free survival (PFS) for estrogen receptor (ER)+ advanced breast cancer (BC), but resistance occurs, and new options are needed in the post-CDK4/6i setting. BCL2 is an estrogen-responsive anti-apoptotic molecule overexpressed in 75% of BCs. The BCL2 inhibitor venetoclax (Ven) has shown improved outcomes and tolerability in hematological malignancies such as chronic lymphocytic leukemia, and has been investigated in BC. A phase 1b study of Ven + tamoxifen demonstrated safety and an efficacy signal in ER+, BCL2+ metastatic BC (mBC). Preclinical data for Ven + fulvestrant (Ful) have also shown synergy. Based on these proof-of-principle data, the current study evaluates safety and efficacy of Ven + Ful vs Ful in women with ER+, HER2– locally advanced (LA)/mBC progressing after first- or second-line of prior therapy for metastatic disease, including ≥8 wks of a CDK4/6i. Methods: VERONICA is a global, randomized, phase 2, multicenter, open-label study. Eligible patients (pts) are aged ≥18 yrs with confirmed ER+, HER2–, inoperable LA/mBC, ≥1 measurable lesion, tissue evaluable for BCL2, and ECOG performance status 0–1. Prior Ful or Ven, or prior chemotherapy for LA/mBC are prohibited. Stratified by BCL2 expression (low vs high) and number of prior lines of mBC therapy (1 vs 2), pts are randomized 1:1 to Ven 800 mg PO daily + Ful 500 mg IM (cycle 1 days 1 and 15, and day 1 of each subsequent 28-day cycle) vs Ful 500 mg IM alone. Treatment continues until disease progression or intolerable toxicity. Primary endpoint is clinical benefit rate defined as complete/partial response + stable disease for ≥24 wks from randomization. Secondary efficacy endpoints include PFS, objective response rate, duration of response, and overall survival. Safety, pharmacokinetic, biomarker (e.g. BCL2 and PI3K expression) and patient-reported outcome analyses will also be conducted. Currently, 21 of the planned 100 pts have been enrolled; enrollment is ongoing. Clinical trial information: NCT03584009.