A rare case of a superficial squamous cell carcinoma (so-called cloacogenic carcinoma) of the rectum.

A rare case of a squamous cell carcinoma (so-called cloacogenic carcinoma) showing extensive superficial spread to the rectum is presented. A 69-year-old woman had undergone colonoscopy for annual check-up, and a whitish, flat lesion with a central depressed area, 20 mm in size, was identified in the lower rectum. Narrow-band imaging with magnifying observation showed abnormal microvessels without the intrapapillary capillary loop patterns. Endoscopically, the margin of the lesion was unclear. Biopsy was performed, and a histological diagnosis of transitional cell carcinoma was made. Computed tomography showed no evidence of involvement of adjacent organs, lymph nodes or distant sites. Cystoscopy found no abnormality in the bladder mucosa. Owing to difficulty diagnosing this tumor accurately, local excision with transanal endoscopic microsurgery was performed. Cloacogenic carcinoma with submucosal invasion was diagnosed. A human papilloma virus (HPV) polymerase chain reaction test was positive. Judging from the histological findings and the positive HPV test, we hypothesis that the tumor was likely arising from the anal transitional zone with marked superficial spread to the rectum. Clinicians should keep in mind that this variant of squamous cell carcinoma may occur in the rectum, even if no endoscopic findings are seen in the anal transitional zone.