Malignant Transformation to Mucinous Adenocarcinoma in Chronic Fistula-in-ano: Transformation to Mucinous Adenocarcinoma in Chronic Fistula-in-ano

Malignant transformation in chronic fistula-in-ano (FIA) is rare, typically occurring due to long-term inflammation in untreated fistulas, though the exact cause remains unclear. These cancers are often aggressive, and their symptoms can resemble those of a benign fistula, leading to delayed diagnosis. We report a 71-year-old gentleman with supralevator FIA who developed perianal mucinous adenocarcinoma. The patient had suffered from a recurrent fistula for 40 years despite multiple surgeries and presented to our centre with a non-healing FIA. Magnetic resonance imaging (MRI) revealed a complex fistula with several openings, and histopathology confirmed adenocarcinoma with mucinous differentiation. Chronic FIA is a common but its rare potential to transform into perianal mucinous adenocarcinoma emphasizes the need for early detection and intervention. Although uncommon, malignant transformation should be considered in longstanding or recurrent complex FIA, particularly when symptoms persist despite previous treatment. Early imaging, such as MRI, and multiple biopsies are crucial for identifying malignancy and ensuring proper treatment, especially radical surgery.