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Figure 9: Two typical cases of small invasive colorectal cancer (≤5 mm). (A): (a) Conventional view: There is a small polyp (lesion size: 4 mm) located in the sigmoid colon. It is rather difficult to visualize any depressed area in this lesion. (b) NBI view: Magnification with NBI clearly demarcates the margin of the depressed area. The vascular pattern is capillary pattern Type IIIB of the Sano classification, indicative of deep invasion into the submucosa. The center of the depressed area has a dome-like appearance, and the macroscopic type is “0-I s + II c”, which requires attention in view of its frequent deep invasion into the submucosa. (c) Crystal violet view: magnification with crystal violet staining also demonstrates an invasive pattern and VN pits, strongly indicative of deep submucosal invasion. We decided to treat this lesion surgically without endoscopic resection. (d) Pathological findings: well to moderately differentiated adenocarcinoma, pSM (3000–4000 μm), ly(+), v(-), pN0. (B): (a) Conventional view: there is a small polyp (lesion size: 5 mm) located in the descending colon. It is difficult to visualize any depressed area in this lesion. (b) NBI view: magnification with NBI clearly demonstrates a depressed area in the center of this lesion. The vascular pattern in the lesion center is capillary pattern Type IIIB by the Sano classification, suggesting the possibility of invasive cancer. Crystal violet staining is therefore required. (c) Crystal violet view: magnification with crystal violet staining demonstrates an invasive pattern. Invasive cancer cannot be predicted with high confidence because the depressed area is small. This lesion was treated by endoscopic mucosal resection for initial diagnosis, and later the patient underwent surgery. (d) Pathological findings: well differentiated adenocarcinoma with scirrhous growth, pSM massive, VM(+), ly(+), EMR.