Endoscopic Diagnosis and Treatment of Colorectal Cancers Dong Kyung Chang Department of Internal Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea. dkchang@skku.edu Abstract Colonoscopy is the best screening tool to detect colorectal cancer in early stage and also a potent arm to prevent development of cancer by removing colorectal adenoma. Superficial colorectal neoplastic lesions are primary targets of colonoscopic resection. Adenoma, carcinoma in situ, and cancer with minimal submucosal invasion are included in this category. One stage endoscopic treatment without the preceding biopsy confirmation is preferable, and thus endoscopic evaluation to identify the characteristics of the superficial neoplastic lesions is of importance. Gross endoscopic appearance and pit pattern and/or vascular pattern of the surface epithelium of the polypoid and nonpolypoid superficial lesions provide useful clue to predict histology of the lesions and depth of cancer invasion with reasonable accuracy. Appropriate treatment can be directed through this endoscopic evaluation step. Conventional snare polypectomy and endoscopic mucosal resection is mainstay of endoscopic treatment. Recently introduced endoscopic submucosal dissection facilitated en bloc resection of a large neoplastic lesion. After endoscopic resection, accurate pathologic evaluation is necessary to determine whether colonoscopic follow up or further surgical resection is needed. Poorly or undifferentiated cancers, cancers massively invading submucosal layer deeper than 1,000 micrometer, lymphovascular invasion of cancer cells, or presence of cancer cells on the resection margin are indications of further surgical resection because of the significant risk in metastasis to the regional lymph nodes. Colorectal polyps and early cancers are effectively treated by colonoscopy in most cases. Early detection by an adequate screening program is essential for this purpose. Key Words: Colorectal polyp, Colorectal cancer, Colonoscopy, Polypectomy, Endoscopic submucosal dissection