Final analysis of dose-finding and single-arm confirmatory study (phase I/II study) of definitive chemoradiotherapy (dCRT) with S-1/mitomycin-C (MMC) in patients (pts) with clinical (c) Stage II/III squamous cell carcinoma of the anal canal (SCCA): JCOG0903.
Authors: Ito Yoshinori , Hamaguchi Tetsuya , Takashima Atsuo , Mizusawa Junki , Shimada Yasuhiro , Shiozawa Manabu , Kodaira Takeshi , Ohue Masayuki , Kinouchi Makoto , Murata Kohei , Iinuma Gen , Fujita Fumihiko , Miura Hirohisa , Ishida Fumio , Saida Yoshihisa , Matsuda Takahisa , Katayama Hiroshi , Fukuda Haruhiko , Kanemitsu Yukihide 
Published: June 2021

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Background: dCRT with 5-FU/MMC is a standard treatment for cStage II/III SCCA. S-1 is an oral fluoropyrimidine and has a greater effect on radiosensitivity. We conducted this trial of dCRT with S-1/MMC to determine the recommended dose (RD) of S-1 in dose-finding (phase I) part and to evaluate the efficacy and safety in confirmatory (phase II) part for cStage II/III SCCA. We reported the RD of S-1 and the 3-year survival at 2019 Gastrointestinal Cancers Symposium. We report the final data after 5-year follow-up. Methods: Eligibility criteria included histologically proven SCCA, cStage II/III (UICC 6th), PS 0-1, and age 20-80 years. dCRT consisted of MMC (10 mg/m2 on days 1, 29) and S-1 (60 mg/m2/d in level 0 and 80 mg/m2/d in level 1 on days 1-14, 29-42) with concurrent radiotherapy of 59.4 Gy/33fr. The dose-finding part adopted the 3+3 cohort design. The primary endpoint of confirmatory part was 3-year event-free survival (EFS). The sample size was 65 in the confirmatory part, with one-sided alpha of 5% and power of 80%, threshold and expected 3-year EFS as 60% and 75%. Key secondary endpoints were overall survival (OS) and progression-free survival (PFS) and colostomy-free survival (CFS), and adverse events. Final analysis was planned after 5-year follow-up for all pts. Results: From Feb/2010 to Mar/2015, 69 pts (3 in level 0 and 66 [7 in phase I and 59 in phase II] in level 1) were enrolled. Pts characteristics for level 1 were as follows: M/F, 12/54; Age, median 64 (range 33-80); cStage II/IIIA/IIIB, 29/9/28. Three in level 1 were ineligible and 63 eligible assigned to level 1 were included in efficacy analysis. In the dose-finding part, RD of S-1 was determined as 80 mg/m2/d. The complete response rate was 81% (95% CI, 69.1-90.0%) on central review. With a median follow-up of 5.4 years, 3- and 5-year EFS was 65.0% (90% CI 54.1-73.9%) and 63.4% (95% CI 50.2-73.9%). 5-year OS, PFS, and CFS were 84.1% (95% CI 72.5-91.1%), 84.1% (95% CI 72.4-91.1%), and 73.0% (95% CI 60.2-82.3%), respectively. In a univariable analysis, male sex (p = 0.045) prognosticated for poor OS and cT3 or T4 (p = 0.001), male sex (p = 0.019) and, PS 1 (p = 0.048) prognosticated for poor CFS. Nine (14.3%) of 63 pts at a dose level 1 developed recurrence or disease progression. Locoregional recurrence only and distant metastasis were observed in 1 pts (1.6%) and 8 pts (12.7%) respectively. Among all treated 65 pts, only 5 pts (7.7%) showed grade 3 late toxicities including jejunum obstruction, jejunum ulcer, proctitis, lower gastrointestinal hemorrhage, anal pain, radiation dermatitis, and ureteral stenosis. No Grade 4 or 5 late toxicities were observed. Conclusions: dCRT with S-1/MMC showed acceptable toxicities and favorable 5-year survival and could be a possible treatment option for pts with locally advanced SCCA. Clinical trial information: jRCTs031180002.