P090 Anal Fistula Cancer of Luminal Origin Associated With Crohn's Disease: A Case Report. (December 2019) - Shinozaki, Masaru
Abstract : CASE: Recent studies have shown that the risk of anal fistula cancer, as well as colorectal cancer, is increased in patients with Crohn's disease (CD) compared with that in the general population. The prognosis of patients with anal fistula cancer associated with CD is generally poor, and its natural course has not been clarified yet. Herein, we report a case of anal fistula cancer and rectal tumor associated with CD, which shared the same genetic mutations. A Japanese man was diagnosed with CD at the age of 25 years. When he was 38 years old, he underwent a subtotal colectomy, ileo-sigmoid colonic anastomosis for entero-entero fistula, and seton drainage for anal fistula. He received maintenance therapy consisting of azathioprine and infliximab. Additionally, annual surveillance colonoscopy had been performed. When he was 44 years old, a small reddish, slightly depressed area very close to the dentate line was detected. Although the lesion did not appear to change in size for 2 years, it got larger, and the surface pattern was indicative of neoplasm, when he was 47 years old. The tumor was biopsied for the first time, which revealed high-grade dysplasia. The patient agreed to undergo excisional biopsy under spinal anesthesia. The operation was performed as follows: after the tumor was excised, we changed our gloves and instruments and sterilized the surrounding area with povidone iodine to avoid contamination. We explored the fistula with curettage, since its primary orifice was located very close to the tumor. We also removed the surrounding mucosa separately. The biopsy specimens were submitted for pathological review. The tumor revealed high-grade dysplasia, which was restricted to the mucosal layer, and the specimen from the anal fistula also showed high-grade dysplasia. Computed tomography or magnetic resonance imaging scans revealed no evidence of malignancy. Therefore, we recommended him to undergo abdominoperineal resection to check for possible cancer at the anal fistula, for which the patient agreed. The specimen of the abdominoperineal resection showed that the remaining cancer extended to the anal fistula. The cancer spread infiltratively, spanning approximately 1 cm × 2 cm without mass formation. The histology findings revealed well-differentiated adenocarcinoma and mucinous adenocarcinoma. We performed a genetic analysis of the polypoid tumor and the anal fistula cancer. The results showed that the same somatic mutation, c.1015_1016insCTTCG, in the TP53 gene was identified in both tumors but not in the paired non-cancerous tissue, suggesting that the tumors originated from the same neoplastic cell. The morphological progression detected through the surveillance colonoscopy suggested that the polypoid tumor was the primary lesion, and the anal fistula cancer was a spread or metastasis of the polypoid lesion. Therefore, some anal fistula cancers may be of luminal origin.