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.

775Background: 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 ...