A case of rectal tumor in which the shape altered with regression in short period

BACKGROUND: Histological regression of solid tumors in adults receiving no treatment is rare. Specifically, spontaneous partial and complete regression of colorectal cancers account for less than 2% of such cases and those without metastasis are exceedingly rare. CASE PRESENTATION: A 60-year-old male underwent total colonoscopy following a positive fecal occult blood test at the referring hospital. A flat elevated lesion with central reddish depression, 10 mm in diameter, was detected in the lower rectum. Biopsy results from the referring hospital showed a well-differentiated adenocarcinoma and the patient was referred to our hospital for diagnosis and treatment. Preoperative colonoscopy was performed to determine the therapeutic strategy; however, we found only scar tissue and there were no endoscopic features to suggest malignancy. Biopsy from the scar revealed normal rectal mucosa and we performed diagnostic endoscopic submucosal resection with a ligation device (ESMR-L) one week later. The resected specimen showed a 1 mm well-differentiated adenocarcinoma with low-grade atypia and no lymphovascular invasion. The macroscopic type was 0-IIb, the depth of invasion was intramucosal, and the vertical and lateral margins were negative. There has been no evidence of recurrence for 18 months following treatment. CONCLUSION: We report a case of a rectal tumor showing regression over a short period without treatment. Spontaneous regression of malignant tumors is a rare and unexplained phenomenon. Further research and understanding of the mechanism holds the key for treatment and prevention of cancer in the future.