Abstract
More than 20 years have passed since the term “laterally spreading tumor (LST)” was originally proposed by Kudo, et al., and its clinical significance has been recognized worldwide. An LST is defined as a colorectal tumor larger than 10 mm in diameter that tends to extend laterally/horizontally, rather than vertically in the colorectum. In July 2013 the term “LST” was described in the Japanese Classification of Colorectal Carcinoma, 8th Edition. The definition of “LST” is an appellation for superficially spreading tumors and not for macroscopic classification. LSTs are divided into two subtypes based on their detailed endoscopic appearance : granular type (LST-G), which has even or uneven nodules on the surface, and non-granular type (LST-NG), which has a smooth surface. Furthermore, each type has two subtypes : LST-G consists of a “homogeneous type” and a “nodular mixed type”, while LST-NG consists of a “flat elevated type” and “pseudodepressed type”. The subclassification provides clinically important information in determining the appropriate therapeutic strategy. However, in some cases, the diagnoses of the subclassifications (especially for LST-G subclassification) are not consistent among endoscopists or institutions. In this review, we clarify the current issues regarding subclassification of LSTs and propose objective subclassification criteria of LST-Gs based on the size of granules or nodules in relation to their clinical significance.
