Diagnosis of laterally spreading tumors (LST) in the rectum and selection of treatment: characteristics of each of the subclassifications of LST in the rectum

Background: In recent years, endoscopic submucosal dissection (ESD) has often been used for the treatment of laterally spreading tumors (LST) of the rectum. The present study was carried out with the aim of clarifying the characteristics of each of the subtypes of LST in the rectum that are often treated by ESD.

Patients and methods: This study involved 141 rectal LST that were initially treated at our hospital between March 2005 and December 2010 and whose endoscopic images and histopathological specimens could be re-examined. The LST were divided into LST-G-H (homogeneous type), LST-G-MIX (nodular mixed type), LST-NG-F (flat type) and LST-NG-PD (pseudo-depressed type) type lesions, and tumor diameter and depth of invasion of each of these tumor types were investigated.

Results: Regarding the depth of invasion, the proportion of submucosa-massive (SM-m) lesions was high in the LST-NG-PDtumors, even among tumors measuring <20 mm in diameter; both the rate of cancer and proportion of SM-m lesions were significantly higher in the LST-NG-PD tumors than in the LST-NG-F tumors (P < 0.05). In both LST-NG-MIX and LST-NG-PD tumors, the proportion of SM-m lesions was significantly higher in the lower rectum than in the upper rectum (P < 0.05).

Conclusion: For LST of the rectum (particularly of the lower rectum), it is necessary to carefully select the treatment considering LST subclass and tumor diameter from the standpoint of the presence of malignancy, quality of life, and prognosis of patients.