eP127 - Medullary Colon Cancer Presenting as a Diverticular Abscess: A Case Report

Purpose/Background: Medullary colon cancer (MCC) is a rare, poorly differentiated non-glandular carcinoma characterized by high grade, uniform sheets of eosinophil neoplastic cells with a distinct immunohistochemical profile. MCCs are more frequently found in the elderly, females, and in the right colon, but with overall favorable survival characteristics compared to high grade colonic adenocarcinoma. Due to its rarity, unique patient presentations provide opportunities for increased understanding of MCC.

We present a 63-year-old female who presented to our hospital following failed conservative management of a presumed diverticular abscess, ultimately found to have perforated MCC.Methods/Interventions: A 63-year-old female with history of pan-diverticulosis, appendectomy, and prior colonoscopic perforation and sigmoidectomy presented to our hospital after two recent admissions for medical management of a transverse colon diverticular abscess with ongoing abdominal pain, nausea and diarrhea. Upon admission, her vitals and labs were unremarkable, except for a persistent anemia (Hgb 11.3). Her CEA was normal at 1.3 ng/mL. Her CT abdomen/pelvis showed a stable 3 cm intramural abscess with nodular focus and moderate proximal stool burden, increasingly concerning for malignancy. A colonoscopy identified a completely obstructing mass at 60 cm from the anus. She was taken to the OR for exploratory laparotomy, where a large perforated proximal transverse colon mass was identified with notable local desmoplastic reaction infiltrating the mesocolon, adjacent distal small bowel with associated mesentery. The necrotic tumor was able to be isolated off the adjacent small bowel and a right colectomy with high pedicle ligation performed. Her postoperative course was unremarkable.Results/Outcomes: The patient’s surgical pathology revealed a 6.5 cm medullary carcinoma with pericolic tissue invasion with associated sub-serosal abscess, granulation tissue, foreign body material and giant cell reaction consistent with perforation but with negative margins and 0/19 lymph nodes containing carcinoma. Imunohistochemistry demonstrated absent expression of MLH1 and PMS2. She was referred to medical genetics and KRAS staining was pending at the time of this report.Conclusion/

Discussion: MCC is a rare diagnosis (5-8/10,000 colon cancer) and has histopathologic features like those of poorly differentiated or undifferentiated adenocarcinomas. However, these tumors are clinically distinct from adenocarcinoma, including having greater association with microsatellite instability (MSI) and more favorable overall survival. As such, it remains critical for surgeons and pathologists to consider the diagnosis of MCC when encountering a high grade, proximal colon cancer with MSI-H but without local or distant metastatic disease.