Management of early rectal cancer with massive submucosal invasion using endoscopic intermuscular dissection: a case report.

The management of early rectal cancer is shifting toward organ-preserving strategies. Endoscopic submucosal dissection (ESD) achieves en bloc resections for low-risk T1 lesions, while surgery remains the gold standard for deep submucosal invasion due to the risk of nodal metastasis. Endoscopic intermuscular dissection (EID) has emerged as an alternative in selected high-risk patients. We report the case of a 71-year-old man with chronic kidney disease and ischemic heart disease, in whom a 15 mm sessile rectal lesion with features of deep invasion was detected. EID achieved complete resection without complications, and MRI confirmed cT1-2N0 disease. Histopathology revealed moderately differentiated adenocarcinoma with deep invasion, lymphovascular invasion, and grade 2 tumor budding. Given surgical contraindications, active surveillance was chosen after multidisciplinary discussion. At six months, the patient remains recurrence-free. Unlike conventional ESD, EID allows dissection between the inner circular and outer longitudinal muscle layers, improving deep margins in sm2-sm3 lesions. Evidence suggests that lymphovascular invasion, tumor budding, and poor differentiation are the strongest predictors of nodal metastasis. In selected patients, EID may provide curative resection while avoiding major surgery. Careful risk stratification and multidisciplinary evaluation are essential to balance oncologic safety and organ preservation.