Frequent Intraluminal Growth of Large Muscular Veins in Surgically Resected Colorectal Cancer Tissues: A 3-Dimensional Pathologic Reconstruction Study.

Although venous invasion (VI) is common in colorectal cancers (CRCs) and is associated with distant metastasis, the 3-dimensional (3D) microscopic features and associated mechanisms of VI are not well elucidated. To characterize the patterns of VI, 103 tissue slabs were harvested from surgically resected CRCs with ≥pT2. They were cleared using the modified immunolabeling-enabled 3D imaging of solvent-cleared organs method, labeled with multicolor fluorescent antibodies, including antibodies against cytokeratin 19, desmin, CD31, and E-cadherin, and visualized by confocal laser scanning microscopy. VI was classified as intravasation, intraluminal growth, and/or extravasation, and 2-dimensional and 3D microscopic features were compared. VI was detected more frequently in 3D (56/103 [54.4%]) than in conventional 2-dimensional hematoxylin and eosin-stained slides (33/103 [32%]; P < .001). When VI was present, it was most commonly in the form of intraluminal growth (51/56), followed by extravasation (13/56) and intravasation (5/56). The mean length of intraluminal growth was 334.0 ± 212.4 μm. Neoplastic cell projections extended from cancer cell clusters in the connective tissue surrounding veins, penetrated the smooth muscle layer, and then grew into and filled the venous lumen. E-cadherin expression changed at each invasion phase; intact E-cadherin expression was observed in the cancer cells in the venous walls, but its expression was lost in small clusters of intraluminal neoplastic cells. In addition, reexpression of E-cadherin was observed when cancer cells formed well-oriented tubular structures and accumulated and grew along the luminal side of the venous wall. In contrast, singly scattered cancer cells and cancer cells with poorly defined tubular structures showed loss of E-cadherin expression. E-cadherin expression was intact in the large cohesive clusters of extravasated cancer cells. However, singly scattered cells and smaller projections of neoplastic cells in the stroma outward of venous wall showed a loss of E-cadherin expression. In conclusion, VI was observed in more than half of the CRCs analyzed by 3D histopathologic image reconstruction. Once inside a vein, neoplastic cells can grow intraluminally. The epithelial-mesenchymal transition is not maintained during VI of CRCs.