The Role of Histopathology in the Management of Malignant Colorectal Polyps

H.S. Cooper, Dept. of Pathology, Fox Chase Cancer Center, Philadelphia, PA, USA

The histopathological interpretation is extremely important in the management of the patient with an endoscopically removed malignant polyp. A malignant polyp of the colon or rectum is defined as a lesion in which cancer has invaded through the muscularis mucosae and into the submucosa (pT1). This process involves the technical handling of the specimen, communication with the endoscopist, and finally histopathological interpretation. The specimen requires an adequate time of fixation so that it can be sectioned properly. Communication with the clinician as to whether the specimen was removed in one piece or piecemeal is essential. The histopathological parameters that one traditionally examines are 1) status of the margin of resection, 2) grade of the cancer, and 3) lymphatic and/or venous invasion. Presently there is no consensus as to what defines tumor at or near a margin. Some investigators define this as tumor less than or equal to 1 mm, less than or equal to 2 mm, or cancer within the cautery of the transected margin. The incidence of adverse outcome (tumor metastatic to lymph nodes and/or residual tumor in the resection site) is approximately 20% in those malignant polyps with any unfavorable histological features (tumor at or near the margin or grade 3 cancer or lymphatic invasion) and 0% in those without unfavorable histopathological features. The interobserver variation is substantial to excellent for accessing grade and the status of the margin, but fair to substantial for diagnosing lymphatic invasion. Recently other investigators have reported; 1) depth of submucosal invasion (> 2.0 mm), 2) the presence of tumor budding, and 3) depth of lymphatic invasion (> 2.0 mm) as unfavorable histological parameters which are significantly associated with an adverse outcome. Patients with unfavorable histopathological features are probably best managed by resection post polypectomy, whereas in the absence of unfavorable histological features, polypectomy alone is adequate treatment.

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