A case of early rectal carcinoma with submucosal tumor-like morphology.

Submucosal tumor (SMT)-like colorectal cancer is relatively rare. The patient was a 59-year-old man who underwent colonoscopy after a positive fecal occult blood test. Colonoscopy showed a protruded lesion of 10 mm in the lower rectum. On initial observation, conventional endoscopy showed that the lesion was covered with normal mucosa and its surface was reddish with small dimples. A neuroendocrine tumor was suspected, and a biopsy was performed, but the pathological diagnosis was adenocarcinoma. Re-examination 3 weeks later showed a depression at the surface of the lesion owing to the biopsy. Magnifying NBI showed a vessel pattern of uneven and irregular distribution, and an irregular surface pattern in the depressed area. Magnifying observations with crystal violet staining showed irregular pit patterns. The preoperative diagnosis was submucosal invasive cancer, and operation was performed. The final pathological diagnosis was well-differentiated tubular adenocarcinoma with deep submucosal invasion. The tumor was primarily localized in the submucosal layer and was covered by non-neoplastic mucosa except for the depressed area. The tumor was not exposed on the surface and was proliferating under the mucosa, which resulted in an SMT-like morphology. Our present case indicates that colorectal cancers should be differentially considered when SMT lesions are detected.