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A case of mucinous adenocarcinoma arising on a long-standing anorectal fistula is described. A 60-year-old man with a long history of mucinous discharge, pain and perianal induration underwent a biopsy of the external opening of the fistula that showed a mucinous infiltrating adenocarcinoma. Due to the large size of the tumor and the fact that it had extended into the surrounding tissue, preoperative radiotherapy was performed. Radiotherapy was given with 40 Gy in 25 fractions for 5 weeks through posterior and bilateral portals. After radiotherapy the tumor was markedly shrunk and the serum level of carcinoembryonic antigen was also improved. Abdominoperineal resection was performed 8 weeks after the termination of radiotherapy. Histological examination of the resected specimen revealed that the invasion of the tumor remained within the sphincter muscle and that no cancer cells were present on the surgical margin. The histological effect of radiotherapy was judged as grade 1b. This treatment can result in downstaging and R0 resection, which also has a possibility to prevent local recurrence. This case suggests that preoperative radiotherapy may play an important role in the definitive treatment of locally advanced perianal mucinous adenocarcinoma.

A 65-year-old woman underwent iliocecal resection for cecal cancer. During post-operative follow-up, she was diagnosed with metastasis to the abdominal wall and a curative resection was performed. After 12 courses of adjuvant chemotherapy with a modified combination of folinic acid, 5-fluorouracil, and oxaliplatin (mFOLFOX6), recurrence was noted in the lung. A curative resection was successfully performed and she was subsequently treated with bevacizumab and a combination of folinic acid, 5-fluorouracil, and irinotecan (FOLFIRI). One year after surgical resection, recurrence in the remnant lung was diagnosed. Because of the KRAS mutation, she could not be treated with anti-epidermal growth factor antibodies. The metastatic lung tumor continued to enlarge. Therefore, we selected regorafenib as third-line chemotherapy. After treatment with regorafenib, the size of the target lesion decreased significantly.