Phase III trial of a 3-weekly versus 5-weekly schedule of S-1 plus cisplatin (SP) combination chemotherapy for first-line treatment of advanced gastric cancer (AGC): SOS study.

Abstract

LBA4024 Background: 5-weekly S-1 plus cisplatin (SP5: S-1 80-120 mg/body/day on D1-21, cisplatin 60 mg/m2 on D8, every 5 weeks) has become a standard first-line chemotherapy for AGC in Japan based on the SPIRITS trial (Lancet Oncol. 2008;9:215). To strengthen the low-dose intensity of cisplatin in this SP5 for greater efficacy, a 3-weekly S-1 plus cisplatin (SP3: S-1 80 mg/m2/day on D1-14, cisplatin 60 mg/m2on D1, every 3 weeks) has been developed in Korea (Cancer Chemother Pharmacol. 2008;61:837). Methods: This SOS study was a multicenter, randomized, open-label, phase III study to evaluate whether SP3 was non-inferior/superior to SP5 in terms of progression-free survival (PFS) determined by a blinded central radiology review according to RECIST v1.1. Patients (pts) with metastatic or recurrent gastric or gastroesophageal junction adenocarcinoma and with no prior chemotherapy were randomized 1:1 to receive either SP3 or SP5 until disease progression or unacceptable toxicities. Results: Between February 2009 and January 2012, a total of 625 pts were randomized from 42 sites in Korea and Japan. Median age was 59.6 years. 99% of pts had ECOG performance status 0-1. 16% of pts had prior gastrectomy. 62% of pts had measurable lesions. With a median follow-up of 34.7 months (range, 14.2-48.8) in surviving pts, SP3 was significantly noninferior and superior to SP5 in PFS (median 5.5 months vs. 4.9 months; HR 0.82, 95% CI 0.68-0.99, p=0.0418). Overall response rate (ORR) was also better with SP3 than with SP5 (60% vs. 50%, p=0.029). However, OS of both groups was equivalent (median 14.1 vs. 13.9 months; HR 0.99, 95% CI 0.81-1.21, p=0.9068). Treatment was well tolerated in both arms, while SP3 was associated with more frequent G3/4 anemia (19% vs. 9%) and neutropenia (39% vs. 9%). Dose intensity was higher in SP3 than in SP5 for both agents (median 331 vs. 317 mg/m2/week for S-1, p<0.001; median 18 vs. 12 mg/m2/week for cisplatin, p<0.001). Conclusions: SP3 was noninferior and superior to SP5 in terms of PFS and ORR. However, considering the small benefit in PFS and no difference in OS, both SP3 and SP5 can be recommended for the first-line treatment of AGC. Clinical trial information: NCT00915382.