[A case report of metastatic anal fistula cancer treated with neoadjuvant chemotherapy]

A 69-year-old man with perianal pain was diagnosed with an anal fistula and a rectal tumor by magnetic resonance imaging and pulmonary tuberculosis by computed tomography. A colonoscopy confirmed the presence of a circular mass in the rectum 6 cm from the anal verge. Histological examination revealed a moderately differentiated adenocarcinoma. Initially, seton drainage was used to improve the perianal pain. After 2 months of anti-tuberculosis therapy, the patient underwent low anterior resection for the rectal cancer. Six months after surgery, a perianal tumor was detected at the postoperative site of the anal fistula. Biopsy of the tumor revealed adenocarcinoma. Because the histological appearance of the second tumor was identical to the rectal cancer, it was diagnosed as a metastatic anal fistula cancer. The tumor shrunk after 3 courses of neoadjuvant chemotherapy with S-1 plus oxaliplatin (SOX) plus bevacizumab and there was no evidence of distant metastasis. Local resection of the anal fistula cancer was performed. Six months postoperatively, the patient is doing well and shows no sign of recurrence.