Low-grade appendiceal mucinous neoplasm associated with ulcerative colitis: A case report and literature review.

Rationale: Colorectal cancer (CRC) development is a critical prognostic factor for patients with ulcerative colitis (UC), making its early detection important. However, early detection of CRC is clinically challenging. This case report describes a patient diagnosed with transverse colon cancer and a low-grade appendiceal mucinous neoplasm (LAMN) in the context of pancolitis-type UC.

Patient Concerns: A 59-year-old male patient with a 24-year history of pancolitis-type UC was referred to our hospital after a routine surveillance colonoscopy for the first time in 5 years revealed transverse colon cancer.

Diagnoses: Colonoscopy revealed type 3 advanced carcinoma in the transverse colon and a protruding lesion resembling a laterally spreading granular tumor at the appendiceal orifice. Computed tomography demonstrated enlargement of the appendix.

Interventions: The patient underwent laparoscopic total colectomy, lymph node dissection of transverse colon cancer, ileal pouch-anal anastomosis, and temporary ileostomy.

Outcomes: The patient was diagnosed with stage IIA transverse colon cancer. Additionally, the appendiceal lesion was diagnosed as a LAMN, a relatively novel pathological entity considered a precursor to appendiceal mucinous adenocarcinoma.

Lessons: Although the appendix is part of the colon and can serve as a site for UC-CRC development in patients with pancolitis-type UC, identifying appendiceal lesions through routine surveillance comprising colonoscopy alone may be challenging. In patients with pancolitis-type UC, lesions known as LAMN, which are recognized as precursors of appendiceal mucinous adenocarcinoma, may develop, thereby requiring careful monitoring.