Fistula-Associated Perianal Mucinous Adenocarcinoma

Area of Science:

• Gastroenterology
• Oncology
• Pathology

Background:

• Perianal mucinous adenocarcinoma is rare and often misdiagnosed as perianal fistulas.
• Its etiology and diagnostic criteria require further elucidation, particularly in fistula-associated cases.
• Previous research focused on clinical and radiological aspects, with limited histopathological detail.

Purpose of the Study:

• To investigate the histopathologic and immunohistochemical characteristics of primary fistula-associated perianal mucinous adenocarcinoma.
• To establish distinct diagnostic criteria for this uncommon entity.
• To explore potential precursor lesions and associations with chronic fistulas.

Main Methods:

• Retrospective review of perianal carcinomas over 15 years.
• Detailed histopathologic examination of tumor morphology, including mucin pools and epithelial growth patterns.
• Immunohistochemical analysis using a panel of markers (CDX2, keratins, mucins, beta-catenin, AMACR, GCDFP15, MUC6).

Main Results:

• Identified 3 male patients with primary fistula-associated perianal mucinous adenocarcinoma (average age 55).
• Patients had long-standing, nonhealing fistulas linked to hidradenitis suppurativa and Crohn's disease.
• Tumors were low-grade, well-differentiated, showing continuity with epidermis, intestinal metaplasia, and a specific immunophenotype (CDX2+, K7+, K20+, MUC1+, MUC2+, MUC5AC+, beta-catenin+, AMACR-, GCDFP15-, MUC6-).

Conclusions:

• Primary fistula-associated perianal mucinous adenocarcinoma possesses distinct clinicopathologic and immunohistochemical features.
• Chronic, nonhealing fistulas, especially in patients with hidradenitis suppurativa or Crohn's disease, should raise suspicion for this entity.
• Understanding these features aids in accurate diagnosis and differentiation from secondary carcinomas and benign fistulous disease.