Early invasive carcinoma in colonic polyps. A review of the literature with emphasis on the assessment of the risk of metastasis.

The proper treatment of adenomatous colonic polyps containing small foci of invasive cancer is controversial because the metastatic potential of these lesions is not precisely known. This article critically reviews all known English language studies of this lesion. Before the introduction of colonoscopic polypectomy, the estimated incidence of metastasis from this lesion was 10.4% (based on 12 studies containing 347 polyps), with a confidence interval (95% level) of 7.4 to 14.1. The incidence of metastasis estimated from lesions removed via colonoscopic polypectomy was 10.1% (based on 13 studies containing 188 polyps), with a confidence interval of 5.9 to 14.8. Differences in the definitions of the involved lesions, study designs, and indications for resection cause problems with case selection bias and make comparison of studies difficult. These problems are discussed in detail. Most studies had broad confidence intervals for the estimated incidence of metastasis because of small sample size. The histopathologic criteria, as reflected in the literature, for considering polypectomy alone as adequate treatment for this lesion are summarized and discussed.