A phase-I study of second-line S-IROX for unresectable pancreatic cancer after gemcitabine plus nab-paclitaxel failure

Gemcitabine plus nab-paclitaxel (GnP) and FOLFIRINOX are widely used as first-line regimens for unresectable pancreatic cancer (PC). When GnP therapy is selected, considering patient age or condition, second-line FOLFIRINOX is sometimes difficult to administer owing to its toxicity. This study aimed to determine the recommended dose (RD) of S-IROX (S-1, oxaliplatin, and irinotecan combination) regimens in patients with unresectable PC after first-line GnP failure. This phase-I study used the “3 + 3” dose-escalation design with two dose levels. Patients who failed first-line GnP therapy for unresectable PC were enrolled. Oxaliplatin and irinotecan were administered on day 1, and S-1 was administered orally twice daily on days 1–7, followed by 7 days of rest. The primary endpoints were dose-limiting toxicities (DLTs) and determination of RD. The secondary endpoint was the evaluation of potential antitumor activity. Nine patients received the second-line S-IROX regimen. In level-0 (S-1, 80 mg/m²; oxaliplatin, 85 mg/m²; and irinotecan, 120 mg/m²), no patient experienced DLT; however, one patient experienced grade 3 neutropenia. At level-1 (irinotecan increased to 150 mg/m²), one of six patients experienced DLTs, including G3 diarrhea. The RD was confirmed at the level-1 dose. The response rate, disease control rate, median progression-free survival, and median overall survival were 33.3%, 77.8%, 172 (range:77–422) days, and 414 (101–685) days, respectively. One patient underwent surgery after the second-line S-IROX therapy. Second-line S-IROX treatment was deemed acceptable. The RD was set at level-1 dose (S-1, 80 mg/m²; oxaliplatin, 85 mg/m²; and irinotecan, 150 mg/m²).