Phase I/II study of oral fluoropyrimidine S-1 plus oral Leucovorin as first-line treatment for metastatic colorectal cancer

4093 Background: The results of phase I portion of the treatment with the oral S-1 (a new oral fluoropyrimidine) plus oral leucovorin (LV) in patients (pts) with untreated metastatic colorectal cancer (mCRC) was reported at ESMO 2006. Dose limiting toxicities (DLTs) were grade 3 stomatitis/pharyngitis, nausea, diarrhea, ileus and exanthema. The recommended doses (RDs) for this phase II portion were determined to be S-1 40 mg/m2 and LV 25 mg/body orally given twice daily on days 1 to 14 of a 28-day cycle. The PK profiles of S-1 plus LV were similar to those of S-1 monotherapy and UFT plus LV, respectively. The main purpose of this phase II portion is to evaluate the efficacy and safety of S-1 plus LV at RD level in pts with untreated mCRC. Methods: Pts were eligible as follows; unresectable mCRC with no prior chemotherapy or receiving adjuvant chemotherapy completed at least 6 months before, histologically proven adenocarcinoma, PS(ECOG) 0–2, age 20 to 75, measurable lesions, adequate organ function and written informed consent. The pts received 40 mg/m2 of S-1 plus 25 mg/body of LV twice daily as RD in this phase II portion. The primary endpoint was the objective response rates (RRs), and secondary endpoints were time to progression (TTP) and toxicities. Results: Between Sep 2004 and Jun 2006, 56 pts of 65 enrolled pts received the treatment at RD level. The objective RRs were 55% (36 of 65) for all pts and 55% (31 of 56) for pts at RD. Disease control rates (DCRs) were 86% (56 of 65) for all pts and 86% (48 of 56) for pts at RD. Median TTP was 5.5 months for pts at RD, with a median follow-up of 5.5 months. The median survival time is under observation. During the 6 months from starting the treatment, the most common grade 3/4 toxicities at RD were as follows: diarrhea, 23%; stomatitis, 20%; anorexia, 18%; and neutropenia 13%. Conclusions: A combination of S-1 plus oral LV is an effective, well tolerated, and convenient regimen in pts with untreated mCRC, without the addition of either oxaliplatin or irinotecan. The updated results of the objective RRs, DCRs, TTP reviewed extramurally, and detailed safety profile will be presented at the meeting. This trial was supported by Taiho pharmaceutical co., Ltd., Tokyo, Japan. No significant financial relationships to disclose.