What is the evidence for chemoradiation as definitive treatment for adenocarcinoma arising within a chronic anal fistula

What is known

- Chemoradiation is not established as definitive therapy for fistula-associated anal adenocarcinoma — outcomes come almost entirely from case reports and small pooled case-series, and oncologic surgical resection (typically abdominoperineal resection) remains the standard, with chemoradiation used neoadjuvantly or in patients unfit for/refusing complete resection ^1–4. - Neoadjuvant chemoradiotherapy can produce complete pathologic responses, but this is documented in single cases and small series rather than comparative trials ^1,4.

What is unknown / caveats

- Combining chemoradiotherapy for mucinous subtype is described as 'not well established' in the literature ³ - Evidence is limited to case reports, pooled case series, and narrative/systematic reviews — no RCTs or comparative cohorts - Reported survival with chemoradiation-plus-surgery is heterogeneous (2-44 months in one review) and confounded by selection - Radiotherapy toxicity concerns in IBD patients are raised but derive from single squamous-cell cases, not adenocarcinoma - Whether chemoradiation alone (organ-preserving, definitive) matches resection-based outcomes cannot be answered from these excerpts.

## References

1. Sordo-Mejia R, Gaertner WB. Multidisciplinary and evidence-based management of fistulizing perianal Crohn's disease. World J Gastrointest Pathophysiol. 2014;5(3):239-51. PMID: 25133026.

2. 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.

3. de Souza ABP, Lima AP, Genaro LM, Geiger CPF, Ayrizono MLS, Leal RF. Mucinous adenocarcinoma in perianal fistula in Crohn's disease: Case report and literature review. Int J Surg Case Rep. 2022;95:107211. PMID: 35653944.

4. Dahmeni W, Souilem E, Hassen H, Ghdiri Y, Ahlem Z, Dahmoul A, Slama AB, Brahem A, Jaziri H, Mestiri S, Elleuch N, Hmissa S, Ksiaa M. Complete pathological response to neoadjuvant chemoradiotherapy in Crohn's disease-associated fistula adenocarcinoma: a case report. Front Med (Lausanne). 2026;13:1746760. PMID: 41994432.

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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._