Onset of neutropenia as an indicator of treatment response in the phase 3 RECOURSE trial of trifluridine/tipiracil (TAS-102) versus placebo in patients with metastatic colorectal cancer.
775 Background: TAS-102 is comprised of an antineoplastic thymidine-based nucleoside analog, trifluridine (FTD), and a thymidine phosphorylase inhibitor, tipiracil. Primary results of the RECOURSE trial demonstrated a significant improvement in overall survival (OS) and progression-free survival (PFS) with TAS-102 vs placebo (pbo) in patients (pts) with metastatic colorectal cancer refractory/intolerant to standard therapies. Neutropenia is a common TAS-102–associated adverse event and it has been hypothesized to be associated with a relatively high FTD concentration in pts. Methods: RECOURSE data were analyzed post hoc for correlations between onset of neutropenia (Grade 3/4) and survival benefit. Results: Of 533 pts given TAS-102, 75 (14%) developed Grade 3/4 neutropenia in treatment cycle 1, 86 (16%) for the first time in cycle 2, and 39 (7%) for the first time in cycle ≥3. Onset of neutropenia at any cycle was associated with longer median OS and PFS compared with no neutropenia. A consistent survival benefit was observed regardless of the cycle of initial onset of neutropenia, as demonstrated by the hazard ratio (against cycle-matched pbo control groups) and corresponding median OS differences (Table). Conclusions: An association between occurrence of earliest onset of Grade 3/4 neutropenia and survival benefit was observed. The data indicate that such survival benefit occurred regardless of whether the initial onset of neutropenia occurred after cycle 1, cycle 2, or later. Further analyses are required to fully determine whether FTD pharmacokinetics correlate with TAS-102 efficacy and onset of neutropenia, and whether cycle initiation delays affect response. Clinical trial information: NCT01607957. [Table: see text]