[Squamous cell carcinoma of the anal canal showing complete response after concurrent chemoradiotherapy and S-1 plus mitomycin C - a case report].

The patient was a 65-year-old man who underwent colonoscopy for melena. Following a biopsy, the patient was diagnosed with anal canal squamous cell carcinoma. A computed tomography (CT) scan revealed metastasis to the regional lymph nodes. The proposed treatment regimen comprised radiotherapy combined with S-1 and mitomycin C (MMC). Dur- ing radiotherapy (59.6 Gy in 32 fractions), 10mg/m² MMC was administered, as an intravenous bolus injection, on days 1 and 29. S-1 was administered orally, at a dose of 80 mg/m², on days 1-14 and 29-42. No serious adverse events were observed during chemoradiotherapy; the observed adverse events were leukemia (Grade 2), diarrhea (Grade 1), anorexia (Grade 1), and radiation dermatitis (Grade 1). After 8 weeks of treatment, no tumors, only scar tissue could be detected by using colonoscopy, and a CT scan revealed a remarkable reduction in regional lymph node metastases. The patient achieved a complete response.