Large bowel adenomas containing carcinoma--a diagnostic and therapeutic approach.

Adenomas containing invasive carcinoma of the large bowel form the majority of early colorectal cancers. Conclusive histological diagnosis of early colorectal cancer depends on two conditions; first, the whole lesion must be examined and second the resection margin must border on healthy tissue. The presence of certain histopathological features makes it possible to distinguish between cases with high and low risk of having lymph node metastases. Sixty-six adenomas containing invasive carcinoma are reported. They comprised 3.15% of 2,095 adenomas removed by colonoscopic polypectomy during the same period. Five cases were lost to follow-up. Forty-nine patients considered to be at low risk of having lymph node metastases have been treated by endoscopic polypectomy only with a rigorous follow-up regime including CEA estimation, ultrasonography and total colonoscopy at regular intervals. In none have distant metastases been found on follow-up examinations at a mean duration of 3 years. Two of these cases have developed a metachronous colorectal carcinoma and 15 (30.5%) have metachronous adenomas. Two low risk patients with no tumour found in the operative specimen have undergone major surgical resection. Ten high risk cases have been referred for major surgery and lymph node metastases have been found in four (40%). The need for careful histological examination for lymphatic and veinous invasion is stressed by the presence of this finding in all four high risk patients with involved lymph nodes.