Fig. 3

Vascularization of lung metastases. a Frozen section of a colorectal carcinoma metastasis in the lung. CD31 (vessels, green) and laminin (basement membrane, red) show that normal lung parenchyma is present (left side) next to the tumor tissue (right side). Tumor tissue is recognizable (pale-red) because of the laminin deposited by tumor cells. Alveoli are filled by tumor cells to different extents (asterisks). Scale bar 200 µm. b The peripheral region of a lung metastasis. Alveolar structure is preserved, and capillaries (CD31, green) are located within the alveolar walls (laminin, blue; arrows). The alveolar spaces are filled by tumor cells (propidium iodide, red). Scale bar 20 µm. c Lung metastasis of B16 melanoma cells. Tumor cells are stained by TOTO-3 (blue). Tumor cells (small arrows) can be observed between pneumocytes (podoplanin, green) and the vessel wall (CD31, red). The alveolar structure is mostly disintegrated; however, intact alveolar walls still can be observed (large arrows). Asterisk shows the original alveolar lumen filled by tumor cells. Denuded vessels (small arrowheads) and vessel-free pneumocytes (large arrowheads) are located within the tumor tissue. Scale bar 20 µm. d High-power confocal image of a lung metastasis. This figure shows that both the detached pneumocytes (podoplanin, green; arrows) and the vessel (CD31, blue; arrowheads) have their own basement membrane (laminin, red), and tumor cells are located between them. Scale bar 20 µm