Genotype-driven phase I study of weekly irinotecan in combination with capecitabine-based neoadjuvant chemoradiation for locally advanced rectal cancer.

Purpose: We aimed to identify the maximum tolerated dose (MTD) of weekly irinotecan in combination with capecitabine-based neoadjuvant chemoradiation according to the UGT1A1∗28 genotype in patients with locally advanced rectal cancer.

Patients And Methods: Patients with clinical stage T3-4, N0-2 who were eligible for preoperative chemoradiotherapy were screened for the UGT1A1∗28 genotype. Twenty-six patients with either the ∗1∗1 or ∗1∗28 genotype were eligible for dose escalation of irinotecan, and patients with a ∗28∗28 genotype were excluded. The starting dose of weekly irinotecan was 50 mg/m for the two genotype groups, whereas the dose of capecitabine was fixed at 625 mg/m. Intensity-modulated radiation therapy (IMRT) was applied to the whole pelvis (total dose of 50 Gy in 25 fractions).

Results: The dose of weekly irinotecan was escalated to 95 mg/m in patients with the ∗1∗1 genotype and to 80 mg/m in those with the ∗1∗28 genotype. Dose-limiting toxicities (DLTs) were observed in 2/2 ∗1∗1 patients at 95 mg/m and 2/3 ∗1∗28 patients at 80 mg/m. No DLT cases were observed among the three ∗1∗1 patients at 80 mg/m, and one DLT case was observed among the six patients with ∗1∗28 at 65 mg/m. Hence, 80 mg/m and 65 mg/m were the MTDs for the two groups. The most common grade 3 to 4 toxicities were neutropenia and diarrhea.

Conclusion: A higher dose of weekly irinotecan in combination with capecitabine-based CRT is feasible under the guidance of the UGT1A1∗28 genotype. Further clinical trials at these dose levels are warranted.