Purpose: S-1, a novel oral prodrug of 5-fluorouracil (5-FU), and irinotecan with or without bevacizumab is known to be effective in metastatic colorectal cancer (mCRC). However, it is not clear whether S-1 and irinotecan confers benefits compared to 5-FU and leucovorin plus oxaliplatin (FOLFOX) in patients with mCRC. Our aim was to compare the efficacy and safety of these regimens.
Methods: We analyzed 187 patients with previously untreated mCRC who were enrolled in four phase II studies: SIR (S-1 and irinotecan, n = 40), SIRB (S-1 and irinotecan with bevacizumab, n = 51), FOLFOX (5-FU and leucovorin plus oxaliplatin, n = 46), and STOX (stop-and-go strategy of modified FOLFOX-6 with bevacizumab, n = 50). We evaluated efficacy and safety between SIR/SIRB and FOLFOX/STOX.
Results: Baseline characteristics were similar in the two groups composed of SIR/SIRB (n = 91) and FOLFOX/STOX (n = 96). The overall response rates were not significantly different between the two groups (65% in SIR/SIRB vs. 52% in FOLFOX/STOX, p = 0.125). The median progression-free survival was 10.9 months in SIR/SIRB versus 12.1 months in FOLFOX/STOX (p = 0.59). The median overall survival was 27.3 months in SIR/SIRB versus 26.8 months in FOLFOX/STOX (p = 0.97). Gastrointestinal adverse events were the most common toxicities in SIR/SIRB, while neutropenia and sensory neuropathy were the most common toxicities in FOLFOX/STOX.
Conclusions: S-1 and irinotecan with or without bevacizumab was well tolerated and showed similar response rates and survival compared to the FOLFOX regimen. This combination should be considered as an experimental first-line treatment for mCRC.