1. Background

Although prostate cancer is a common malignancy with well‐established treatment protocols, [1–5] the presence of concurrent anorectal conditions such as perianal fistula can complicate therapeutic decision‐making, particularly when radiation therapy is considered.

Perianal fistula, also known as fistula‐in‐ano is a nonmalignant anorectal condition characterized by pain in the anal and rectal areas, incontinence, and pus discharge [6]. It manifests as a chronic abnormal passage that connects the inner anal lining to nearby skin, forming a narrow channel with openings both inside and outside the anus [6]. This disorder is more common in men. About 12.3 per 100,000 men and 5.6 per 100,000 women are affected by this condition [7]. More than 90% of perianal fistulas originate from cryptoglandular sources [6], with the infection of the intersphincteric glands as the initiating event [8]. Even among experienced colorectal surgeons, surgically treating perianal fistulas can be challenging, resulting in the ongoing debate over the optimal treatment approach [6].

The presence of a pre‐existing perianal fistula may complicate consideration of pelvic radiotherapy due to concerns regarding tissue injury, infection, impaired healing, and fistula progression [9]. To our knowledge, there have been no reported cases of administering radiation therapy for prostate cancer in patients with a pre‐existing, unrelated perianal fistula. However, here, we present a case involving a prostate cancer patient who underwent both radiation therapy and surgical treatment for a pre‐existing, unrelated perianal fistula. Our report adds to the growing body of literature on optimal surgical treatment methods for perianal fistula while providing valuable insights into the management of prostate cancer with concurrent perianal fistula.