Background: Colorectal adenomatous polyps are considered premalignant lesions, although a high percentage are already malignant at the time of their removal. Full-thickness excision in patients with adenoma detected in preoperative biopsy enables much more accurate pathology examination and has shown that local surgery is appropriate for T1 adenocarcinoma.
Objective: To determine whether full-thickness excision during transanal endoscopic surgery is the treatment of choice for rectal adenoma, and to identify possible predictors of invasive adenocarcinoma associated with this type of lesion.
Design: Prospective, observational study.
Setting: The study was conducted at a university teaching hospital.
Patients: All patients scheduled for transanal endoscopic surgery after detection of adenoma in a preoperative biopsy between June 2004 and February 2013 entered the study.
Main outcome measures: The principal variable was the presence of invasive adenocarcinoma in the pathology study. Other study variables were the epidemiological variables sex and age; the clinical variables tumor size, number of quadrants affected, distance from the anal verge, and tumor location; and the morphological variables tumor aspect, degree of dysplasia, preoperative biopsy (tubulo-villous), endorectal ultrasound, and pelvic MRI stage. Variables found to be related to the risk of malignancy in rectal adenomas were evaluated using univariate and multivariate analysis.
Results: Of 471 patients who underwent surgery, 277 had a preoperative diagnosis of adenoma. Final pathology studies showed 52 (18.8%) invasive adenocarcinomas, among which 27 were pT1 (52%), 16 pT2 (30.7%), and 9 pT3 (17.3%). Factors predictive of invasive adenocarcinoma were sessile morphology (OR 3.2, 95%CI 1.4-7.1), high-grade dysplasia (OR 2.3, 95%CI 1.2-4.8), and endorectal ultrasound stage uT2-T3 (OR 3.8, 95%CI 1.6-9).
Limitations: The limitations are derived from the observational design.
Conclusions: In this sample, half of the adenocarcinomas from adenomas were T1 adenocarcinomas. Because a high proportion of rectal adenomas are, in fact, invasive adenocarcinomas, full-thickness excision is appropriate.