Effectiveness of radical surgery after incomplete endoscopic mucosal resection for early colorectal cancers: a clinical study investigating risk factors of residual cancer.

The aim of this study was to determine the need for additional treatment following endoscopic mucosal resection for early colorectal cancer. Risk factors for residual carcinoma were investigated using specimens of curative surgical resection performed after endoscopic mucosal resection. A total of 44 patients who had received imperfect endoscopic mucosal resection initially for early colorectal cancers and, therefore, had undergone subsequent surgical resection were enrolled in this study. Of these, 39 (88.6%) were resected completely by endoscopic mucosal resection based on gross inspection, while the other five cases (11.4%) were incompletely resected. Histopathological examination of specimens of endoscopic mucosal resection revealed that microscopic lateral resection margin was positive in 11 cases (25.0%) and vertical resection margin was positive in 16 cases (36.4%). However, after curative surgery, residual cancer within colorectal tissue was found in only five cases (11.4%), while lymph node metastases were found in three cases (6.8%). Gross incomplete resection (P < 0.001) and microscopic vertical margin positivity (P = 0.031) were found to be risk factors of residual cancer within the colorectal tissue, whereas lymphovascular invasion was a risk factor for lymph node metastasis (P = 0.040). However, no residual cancer cells were found after supplementary surgery in the microscopic lateral resection margin-positive cases. In conclusion, grossly incomplete resection, microscopic vertical resection margin positivity, or the presence of lymphovascular invasion after endoscopic mucosal resection for early colorectal cancer indicate the need for further treatment with surgical resection and lymph node dissection. However, microscopic lateral margin positivity without gross remnant tumor and deep submucosal invasion might not indicate residual cancer. This needs to be further validated by a large scale, prospective study with long-term follow-up.