Natural history of sigmoid colon cancer: report of a patient observed for 4 years.

We report a case of sigmoid colon cancer that was left untreated for a period of 4 years, because the patient declined treatment. A 59-year-old man was found to have an early carcinoma of the sigmoid colon measuring approximately 12 mm in diameter. The lesion, initially a flat cancer, increased in height and became sessile 4 months later. Subsequently, the central portion of the lesion became ulcerated, leaving an elevated ring along its periphery. The lesion eventually evolved into an ulcerated, invasive cancer. This sequence has not been observed with colonoscopy before.