Clinicopathological and Molecular Features of Laterally Spreading Tumors

Colorectal flat-elevated neoplasms can be classified into small-flat adenoma and laterally spreading tumors (LSTs), which can then be sub-categorized into granular-type (LST-G) and nongranular-type (LST-NG) LSTs with possible biological differences between them. We evaluated clinicopathological features and KRAS / BRAF mutations in 24 LST-Gs and 57 LST-NGs. PCR-based pyrosequencing assays were used to determine the presence of activating mutations in codons 12 and 13 of KRAS and in codon 600 of BRAF. Significant differences between LST-Gs and LST-NGs were observed in tumor size (30mm vs. 15mm, P < 0.0001) and the frequency of KRAS mutations (75%, 18/24 vs. 5%, 3/57, P < 0.0001). For LST-NGs, the histological grade was increased with an increase in the tumor size. The frequency of submucosal cancer (SM-ca) was also higher in tumors of at least 20mm than in tumors smaller than 20mm (P < 0.05). In contrast, there was no indication of a size-dependent increase in the histological grade. No significant difference in the frequency of KRAS mutation in LST-Gs and LST-NGs was related to tumor size. Two subtypes of LSTs were observed to have different clinicopathological and molecular characteristics. These findings suggest that different molecular mechanisms could exist in these subtypes of colorectal flat-type neoplasms.