Rectal LST is the abbreviation for lateralized developmental tumor of the large intestine, which is the first type of tumor studied and proposed in Japan. It is a type of flat elevated lesion originating from the mucosa of the large intestine, larger than 10 mm in diameter, with two types of morphology: granular and non-granular. Because the surface of the tumor mainly shows clustering and flattening, depression, etc., it is also called creeping tumor and nodular aggregation type tumor. Compared with other tumors, lateralized developmental tumors of the large intestine do not have normal gene expression profile, tend to spread and develop only on the surface of the rectal wall, rarely invade deeper into the rectal wall, and have the possibility of malignant neoplastic lesions. Currently, the mainstream treatment modalities are surgical and endoscopic minimally invasive treatment. Preoperative pathological biopsy and other related examinations are required to determine whether the tumor is malignant or benign, and then determine the treatment modality.