Clinicopathological differences of laterally spreading tumors of the colorectum according to gross appearance.

BACKGROUND AND STUDY AIMS: Laterally spreading tumors (LST) are classified into two subtypes, with the nongranular type harboring a higher risk of (pre)malignant changes than the granular type. Further subdifferentiation into two subgroups each has been suggested, but the clinical significance of such a subdifferentiation has not previously been studied in detail in larger numbers. PATIENTS AND METHODS: Out of 6499 patients diagnosed with colorectal adenomas between January 2006 and November 2008, 153 patients (2.35 %) had 158 LSTs, 96 with a granular and 62 with a nongranular pattern. The former group was subdivided into homogeneous and nodular mixed, the latter group into flat elevated and pseudodepressed. Clinical and histopathological parameters were compared among the four subtypes.
RESULTS: Parameters were variably distributed between the four groups, with nodular mixed tumors being larger than the other three types ( P < 0.0001). As in other studies, malignant transformation and premalignant lesion (HGIN/CIS) were more frequent in nodular mixed than in homogeneous tumors (45.0 % vs. 5.6 %, P < 0.001), and also more common in pseudodepressed than in flat elevated tumors (41.7 % vs. 13.2 %, P = 0.011). Submucosal invasive cancer was present in 8.3 % of nodular mixed tumors, 7.9 % of flat elevated, and 12.5 % of pseudodepressed, while it was absent in homogeneous tumors. Serrated adenoma was identified in 10.8 % of all LSTs, and sessile serrated adenoma tended to be more common in flat elevated tumors.
CONCLUSIONS: Further subdifferentiation of the LST lesions to identify lesions at risk of malignant transformation makes most sense in the granular type. Among nongranular LSTs, both subtypes carry a significant risk. © Georg Thieme Verlag KG Stuttgart · New York.