EP742 - Deciphering Anal Mucinous Adenocarcinoma Of Uncertain Origin

Monday, May 11, 2026

8:16 AM - 8:21 AM ET

ePoster Presenter(s)

Alexia Benson, MD

Research Fellow
University of South Florida
University of South Florida
Tampa, FL, United States

Disclosure information not submitted.

View ePoster

Senior Author(s)

PC

Paul Cavallaro, MD

Assistant Professor of Surgery
University of South Florida
Tampa, Florida, United States

Disclosure information not submitted.

Author(s)

Taylor L. Garza, MD

Resident
University of South Florida
University of South Florida
Tampa, FL, United States

Disclosure information not submitted.
Robert D. Bennett, MD

Attending Physician
University of South Florida
Tampa, Florida, United States

All disclosed relationships have been reviewed and managed prior to the start of this activity. Any relevant relationships will be listed below. This individual has no financial relationships to disclose

Purpose/Background: Perianal mucinous adenocarcinoma with unknown primary origin is an exceptionally rare malignancy. Early recognition remains challenging, as its presentation often mimics benign inflammatory conditions. A high index of clinical suspicion, supported by histopathologic confirmation, is essential for diagnosis-particularly in patients with chronic ulcerative or proliferative perianal lesions. We describe three complex cases of perianal mucinous adenocarcinoma, each lacking evidence of intraluminal disease.

Methods/Interventions: Case 1: 64-year-old male presented with perianal pain and a large, firm right gluteal mass with fistula tracts extending into the anal canal, pathology consistent with mucinous colonic adenocarcinoma. However, endoscopic evaluation did not reveal any evidence of intraluminal mass. He subsequently underwent a diverting colostomy of the large fistulizing malignancy, followed by neoadjuvant chemoradiation with only a partial clinical response. Given the large disease burden that remained post-therapy, he proceeded with a robotic-assisted extra levator abdominoperineal resection (APR) with flap reconstruction for palliation and symptom control. Case 2: 60-year-old male with a history of fistulizing perianal Crohn's disease presented with a large bulbous/cystic like finding in his left perianal region. Incision and drainage demonstrated a large amount of mucinous material contained within a perianal cavity, along with polypoid tissue within the cavity consistent with tubulovillous adenoma with at least low-grade dysplasia on pathology. Due to ongoing concerns for an underlying malignancy, additional workup and ultimately repeat biopsy revealed invasive mucinous adenocarcinoma with no evidence of intraluminal pathology. Case 3: 46-year-old transgender female with history of HIV and recurrent perianal fistulas was admitted for evaluation of a suspected perianal/perirectal abscess. Examination under anesthesia with incision and drainage revealed copious mucinous drainage from a left perianal cavity. Cytology and biopsies from the perianal cavity confirmed mucinous adenocarcinoma with signet ring cell features.

Results/Outcomes: Following treatment, Case 1 remains under active surveillance with no evidence of disease currently. Case 2 is currently receiving neoadjuvant chemoradiotherapy with stable disease on follow up imaging. Case 3 was subsequently initiated on neoadjuvant chemoradiotherapy with planned reassessment for potential surgical intervention.

Conclusion/Discussion: These cases underscore the diverse clinical presentations of de novo perianal mucinous adenocarcinoma with luminal sparing. Further studies are needed to better define its natural history and guide evidence-based management strategies.

Robotic-assisted extra levator abdominoperineal resection (APR) with flap reconstruction (case 1)

A)Preoperative exam of perineum showing necrotic mucinous tumor

B)Surgical specimen - view from perineal dissection

C)Surgical specimen- lateral view

D)Post anterolateral thigh flap reconstruction of perineum