Abstract
A 64-year-old man who presented with fecal occult blood was admitted to our hospital. Colonoscopy revealed a protruded lesion with decomposition on the dental line. A biopsy sample of the lesion showed normal findings. The patient was diagnosed with mucosal prolapse syndrome (MPS), which progressed during observation. Five months after diagnosis, a biopsy showed that the lesion was ulcerated and malignant. Therefore, we performed perianal local excision of the lesion. Pathological tests revealed evidence of fibromuscular obliteration of the mucosal stroma in the anal canal, and cellular atypia beyond the scope of atypical regeneration. These results indicated well-differentiated tubular adenocarcinoma, which developed as MPS progressed. After excision, all the test results were negative, and the patient was kept under observation. At the time of diagnosis of MPS, it is important to distinguish between MPS and rectal cancer. There are few reports on the progression of MPS to cancer that is diagnosed during follow-up MPS examinations.
