Spontaneous complete regression of a rectal cancer.

We report a unique case of a biopsy-proven rectal cancer exhibiting spontaneous complete regression in an extremely short period of 3 months. An 80-year-old man visited our hospital because of a positive fecal occult blood test. Colonoscopy showed a sessile polyp, about 25 mm in diameter, in the middle part of the rectum. Instead of endoscopic resection, two endoscopic biopsies were taken for histological evaluation, as an invasive cancer was endoscopically suspected.Well-differentiated invasive adenocarcinoma was revealed, and thus surgical resection was planned. At the second colonoscopy for endoscopic tattooing before surgery, the polyp was found to have unexpectedly developed into a flat lesion. Furthermore, the surgically removed specimen showed that the flat lesion had transformed to a depressed lesion, and surprisingly, no cancerous tissue was detected histologically.