In patients with a longstanding anal fistula who develop an ulcerated lesion suspicious for malignancy, is endoscopic ultrasound-guided biopsy or immediate surgical excision preferred

What is known

- Diagnosis of CD-related anal fistula cancer was made via EUA with seton management plus targeted biopsy of ulcerative lesions and random rectal/anal biopsy. ¹ - An MRI 'budding' feature or suspicious findings should trigger EUA and targeted biopsy; inconclusive histology should prompt repeat biopsy +/- enhanced MRI surveillance. ² - Fistula cancers are frequently missed on routine biopsy — cases diagnosed only from the resected specimen despite multiple prior negative biopsies are reported. ^3,4 - Patients with CD >10 years are actively screened by EUA because rectal/anal stenosis often makes colonoscopic access difficult. ¹

What is unknown / caveats

- Evidence is case reports plus one case-control and one small cohort — no comparative or high-level data - The excerpts do not address EUS-guided biopsy specifically - Biopsy can be falsely negative, particularly with acellular mucin from a septic mucinous tract - The excerpts do not compare EUS-guided biopsy against EUA-guided biopsy or immediate excision, so the two options in your question are not directly weighed against each other.

## References

1. Kaneshiro D, Sanechika Y, Kishi K, Sakai D, Iwamoto K, Takeda M, Nakahara Y, Ohashi T, Naito A, Furukawa K, Moon J, Imasato M, Asaoka T, Mizushima T. Crohn's disease-related anal fistula cancer diagnosed by examination under anesthesia: a case report. Surg Case Rep. 2023;9(1):149. PMID: 37610526.

2. Reza L, Corr A, Tozer P, Jenkins JT, Antoniou A, Burns EM, Burling D, Hart A, Clark SK, Lung P. "Budding"-an early MRI feature established in a case-control study of perianal fistula mucinous adenocarcinoma. J Gastrointest Oncol. 2025;16(1):106-114. PMID: 40115924.

3. Inoue T, Sekido Y, Ogino T, Hata T, Miyoshi N, Takahashi H, Uemura M, Mizushima T, Doki Y, Eguchi H. Resection of anorectal fistula cancer associated with Crohn's disease after preoperative chemoradiotherapy: a case report. Surg Case Rep. 2023;9(1):197. PMID: 37962718.

4. Gaertner WB, Hagerman GF, Finne CO, Alavi K, Jessurun J, Rothenberger DA, Madoff RD. Fistula-associated anal adenocarcinoma: good results with aggressive therapy. Dis Colon Rectum. 2008;51(7):1061-7. PMID: 18418652.

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_Draft — generated by the IBDology RAG and not yet clinician-reviewed. Answers are grounded in the retrieved literature listed above; a high faithfulness score means the answer matches its sources, not that the sources are correct._