A phase II trial of trabectedin (T) in patients with hormone receptor-positive, HER2-negative advanced breast cancer, according to xeroderma pigmentosum gene (XPG) expression.

Abstract

TPS652 Background: Hormone receptor-positive, HER2-negative breast cancer (BC) is currently associated with 3-4 years overall survival in the metastatic setting and, after ≥2 relapses, therapeutic approaches are reduced. XPG expression is frequently modified in BC. T is a cytotoxic agent that forms a complex with the XPG, inducing cell apoptosis. As a single agent, T has shown anti-tumor activity in patients with poor prognosis BC, and a better response to T in BC patients with XPG RNA overexpression has been observed. Methods: This is an open-label, phase II study of T (1.3 mg/m2 in 3-hour intravenous infusion every 3 weeks) in patients with hormone receptor-positive, HER2-negative advanced BC, according to their primary tumor’s XPG expression. Primary endpoint: to evaluate the efficacy of T in terms of progression free survival rate at 4 months (PFS4) according to the patient’s XPG expression. Secondary endpoints: Comparison of PFS, overall response rate, duration of response, overall survival and safety profile in XPG-high and XPG-low patients. Assignment: BC patients who have previously received anthracyclins and/or taxanes and who progressed after 2-5 chemotherapy lines will be assigned according to their XPG expression from paraffin embedded tumor samples to stratum A (XPG-high [>3]) or to stratum B (XPG-low [≤3]) (threshold was selected from median XPG expression values observed in a previous trial). Statistical methods: A two-stage design was chosen: at a first stage 20 patients will be enrolled in each stratum. A futility analysis (O’Brien Fleming boundary) based on the primary endpoint (PFS4) will be conducted once 40 evaluable patients have been recruited. If ≥ 7 out of 20 patients achieve PFS4, recruitment will continue to a maximum sample size of 50 evaluable patients per stratum. If ≥ 22 out of 50 patients achieve PFS4, T will be considered active in this group (alpha error: 0.025, power: 80%). To date, 35 patients (16 XPG-high and 15 XPG-low) have been enrolled from three countries and five centers. Recruitment is ongoing.