Purpose: The current study aimed to determine the efficacy of trifluridine/tipiracil for elderly patients with advanced colorectal cancer. Methods: This single-arm, open-label, multicenter, phase II study included elderly patients aged 65 years or more who had fluoropyrimidine-refractory advanced colorectal cancer and received trifluridine/tipiracil (70 mg/m2, days 1–5 and 8–12, every 4 weeks). The primary endpoint was progression-free survival (PFS), while secondary endpoints included overall survival (OS), overall response rate (ORR), toxicities, association between efficacy and geriatric assessment scores, and association between toxicity and plasma drug concentrations. Results: A total of 30 patients with a mean age of 73 years were enrolled. Median PFS was 2.3 months (95% confidence interval, 1.9–4.3 months), while median OS was 5.7 months (95% confidence interval, 3.7–8.9 months). Patients had an ORR of 0%, with 57% having stable disease. Grade 4 neutropenia was observed in 13% of the patients. Patients with a higher G8 score (15 or more) showed longer PFS than those with a lower G8 score (median 4.6 vs. 2.0 months; p = 0.047). Moreover, patients with grade 3 or 4 neutropenia showed higher maximum trifluridine concentrations than those with grade 1 or 2 neutropenia (mean 2945 vs. 2107 ng/mL; p = 0.036). Discussion: The current phase II trial demonstrated that trifluridine/tipiracil was an effective and well-tolerated option for elderly patients with advanced colorectal cancer. Moreover, geriatric assessment tools and/or plasma drug concentration monitoring might be helpful in predicting the efficacy and toxicities in elderly patients receiving this drug. Trial registration number: UMIN000017589, 15/May/2015 (The University Hospital Medical Information Network).
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