Laterally spreading tumors of the colorectum: clinicopathologic features and malignant potential by macroscopic morphology

Laterally spreading tumors (LSTs) are being increasingly reported nowadays. The aims of this study were to analyze the clinicopathologic characteristics and to identify the risk factors of malignancy in patients with LSTs by morphological subclassification. The authors retrospectively reviewed 326 LSTs (287 patients). Patient characteristics, endoscopic findings, and histologic findings were analyzed. Endoscopic findings were subdivided into homogeneous, mixed nodular, flat elevated, and pseudo-depressed subtypes. The clinicopathological features of these subtypes were compared. Of the 287 patients treated, 173 (50.3 %) were male and overall mean patient age was 65 +/- 10 years (ranged 35 to 83 year). Of the 326 LSTs diagnosed, 116 (35.6 %) were homogeneous and 102 (31.3 %) were flat elevated subtype. The location was significantly different among morphological subtype. Tumors of the mixed nodular subtype were significantly larger than the tumors of the other three subtypes (p = 0.00). Of the 326 lesions, 279 underwent endoscopic mucosal resection (granular type 88.1 % (177/201)/nongranular type 81.6 % (102/125)). Two hundred forty-nine lesions (76.4 %) were resected en bloc, and 45 lesions (13.8 %) were resected using the piecemeal technique. Piecemeal resection was significantly more common for the pseudo-depressed subtype (27.0 %, p = 0.00). The overall malignancy rate on a lesion basis was 8.6 %. The malignancy rate increased with lesion size and was higher for the pseudo-depressed (24.3 %) and the mixed nodular subtype (14.1 %). Submucosal invasion was noted for 16 % of pseudo-depressed lesions, and this was significantly higher than the invasion rates of the other subtypes (p = 0.06). By multivariate analysis, morphologic subtype, especially the pseudo-depressed or mixed nodular subtype and size larger than 20 mm were risk factor of malignancy. The clinicopathological features of laterally spreading tumors differ with respect to macroscopic morphology, and the risk of malignant transformation is significantly higher for the mixed nodular or pseudo-depressed subtypes and lesion larger than 20 mm. Careful consideration is required when choosing a treatment modality, and lesions of the mixed nodular and pseudo-depressed subtypes should be completely removed.