Introduction: Adenocarcinoma originating from chronic perianal fistulas is a rare disease. Due to the lack of evidence of this malignancy, no definitive diagnostic and treatment guidelines have been established. We present two cases of anal fistula cancer and discuss the diagnostic and treatment strategies. Presentation of case: A 79-year-old man was referred for a perianal mass. The patient had a history of chronic perianal fistula and was diagnosed with adenocarcinoma originating from a long-standing perianal fistula. The patient underwent laparoscopic abdominoperineal resection (APR) without any adjuvant therapy. The second case was a 42-year old man, who was referred for a prolapsed anal mass. The patient had recurrent perianal fistula over several years. He was diagnosed with mucinous adenocarcinoma originating from a long-standing perianal fistula, but he initially refused surgical treatment. Two years later, the patient revisited with a huge overgrown tumor and underwent laparoscopic APR with wide perineal skin excision, wound debridement and coverage with a bilateral V-Y advancement flap via a one-step procedure. Discussion: High degree of clinical suspicion is crucial to diagnose this rare disease that can easily be missed at an early stage. Depending on the disease stage, surgical treatment, chemotherapy, and radiotherapy can be considered. Conclusion: Histopathological evaluation should be performed on recurrent and incurable anal fistulas over a long period of time. Intensive surgical treatment with or without neoadjuvant and adjuvant therapy should be considered in advanced cases.
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