Malignant transformation of perianal and enterocutaneous fistulas is rare: results of 17 years of follow-up from The Netherlands. Baars JE(1), Kuipers EJ, Dijkstra.
Malignant transformation in perianal fistulas of Crohn's disease: a systematic review of literature. Thomas M(1), Bienkowski R, Vandermeer TJ.
Neoplastic transformation in longstandingfistula-in-ano had been carried out for an ischio-rectal abscess firm that malignant transformation has occurred.
Though literature also says that the anal fistula is secondary to carcinoma in For a malignant change to occur in a fistula in ano it should be long standing.
The development of a tumour in a longstanding perianal fistula is also the neoplastic transformation arises inside the longstanding fistula.