Phase II study of trifluridine/tipiracil (FTD/TPI) in HER2-negative metastatic breast cancers with or without prior exposure to fluoropyrimidines.

Abstract

1099 Background: Fluoropyrimidines are commonly used in the treatment of patients (pts) with metastatic breast cancers (MBC). FTD/TPI is an oral drug combination of trifluridine with tipiracil, a thymidine phosphorylase inhibitor preventing rapid degradation of trifluridine, thus allowing for increased exposure to active agent, and has showed activity in pts with colorectal and gastric cancers despite prior exposure to fluoropyrimidines. We investigate the role of FTD/TPI in MBC pts with (Cohort A) or without (Cohort B) prior exposure to fluoropyridines in a single arm phase II study. Methods: Pts were treated with FTD/TPI, and enrolled first into a lead-in dose confirmation phase, followed by two parallel cohorts based on prior exposure to fluoropyrimidines. Primary objectives for each cohort included determination of progression-free survivals (PFS), and secondary objectives included determination of objective response rates (ORR), safety and tolerability. Results: A total of 74 pts were recruited (42 for Cohort A, 32 for Cohort B), of whom 4 belonged to lead-in phase. Dosing was confirmed at FTD/TPI 35mg/m2 days 1-5 and 8-12 of 4-weekly cycles based on lead-in phase with no dose-limiting toxicities observed, and recruitment then proceeded in 2 parallel cohorts. All pts were evaluable for toxicity and survival analyses, and 72 were evaluable for ORR. Median age at enrolment was 62 years (range 32-85), with median of 4 (range 0-14) prior lines therapy in the metastatic setting, and 47% had de novo metastatic disease. Median PFS was 5.7 months (95% CI 3.8 to 8.3) and 9.4 months (95% CI 5.5 to 14.0) respectively in Cohorts A and B. Similar response rates were observed regardless of prior exposure to fluoropyrimidine, with ORR of 19.5% (95% CI 8.8 to 34.9) and 16.1% (95% CI 5.5 to 33.7) in Cohorts A and B, with 6-month clinical benefit rates of 56.1% (95% CI 39.7 to 71.5) and 61.3% (95% CI 42.2 to 78.2) respectively. Safety profile was consistent with known toxicities of FTD/TPI, with most common treatment-related adverse events of neutropenia, fatigue, nausea and anorexia. 64% of pts required dose modifications during study treatment, most commonly due to neutropenia, that could be overcome by dose reduction or prolongation from 4- to 5-weekly cycles. Only 1 pt required discontinuation due to toxicity from therapy. Conclusions: FTD/TPI showed promising anti-tumor activity with meaningful clinical benefit even among pts with prior exposure to fluoropyrimidines, and has a reasonable toxicity profile with appropriate dose modification. An oral chemotherapy option with good disease control provides an attractive treatment alternative to pts with MBC where quality of life is paramount, warranting further investigation in randomised studies. Clinical trial information: NCT04280536 .