Primary endpoint analysis of a randomized phase II of darolutamide or capecitabine in patients with triple-negative androgen receptor-positive advanced breast cancer (UCBG3-06 START trial)

ABSTRACT

Background: A subgroup of triple negative breast cancer (TNBC) expresses the androgen receptor (AR). In this trial we evaluated the efficacy and tolerability of the AR inhibitor darolutamide (D) or capecitabine (C) in patients (pts) with advanced AR-positive TNBC (NCT03383679). Methods: Pts with centrally reviewed AR-positive (≥ 10% by immunohistochemistry) TNBC treated with up to one line of chemotherapy for advanced disease were eligible. They were randomized in a 21 ratio to receive D 600 mg twice daily or C 1000 mg/m2 twice daily 2-weeks on/ 1-week off, until progression or unacceptable toxicity. Primary endpoint was clinical benefit rate (CBR) at 16 weeks and was assessed in the eligible population and in the sensitivity analysis population (pts with delayed tumour assessment performed in the context of COVID pandemic). Main secondary endpoints included objective response rate, overall survival, progression-free survival (PFS) and safety. Results: A total of 254 pts from 45 centres were screened;94 pts were randomized (61 in D arm, 33 in C arm) from April 2018 to July 2021. A clinical benefit was observed in D arm in 13 of 53 evaluable pts (CBR at 16 weeks 24.5%;95% CI 12.9%-36.1%) including 2 PR and 1 CR and in C arm in 11 of 23 evaluable pts (CBR at 16 weeks 47.8%;95% CI 27.4%-68.2%). In the sensitivity analysis, a clinical benefit was observed in D arm in 17 of 58 evaluable patients (CBR ≥ 16 weeks 29.3%;95% CI 17.6%-41.0%) and in C arm in 19 of 32 evaluable patients (CBR ≥ 16 weeks 59.4%;95% CI 42.3%-76.4%). 7 pts presented with drug-related serious adverse events 3 in D arm and 4 in C arm. In D arm, asthenia (26.7%), nausea (25%) and ASAT increase (21.7%) were the most common adverse events, the majority being grade 1 or 2, similar to previous safety data. Median PFS were 1.8 months (CI 95% 1.7-3.1) and 3.6 months (1.8-9.1) in D arm and C arm respectively. Other secondary endpoints will be presented at the meeting. Conclusions: Despite not reaching the pre-specified CBR, darulotamide demonstrated clinical activity with significant benefit for a group of patients. A research program to identify predictive biomarkers of sensitivity is ongoing. Clinical trial identification EudraCT 2017-002284-18 NCT03383679. Legal entity responsible for the study UNICANCER. Funding: BAYER. Disclosure All authors have declared no conflicts of interest.