Figure 1

Histological staining of BL2B95 tumors on CAM. A (upper part): Panoptic Pappenheim staining of tumor cryosections. The tumor can be divided into a dark stained zone and a central necrotic/hemorrhagic area surrounded by the non-infiltrated CAM. Scale bar = 1 mm. Lower part: Photopgraphs of BL2B95 tumors. B: Panoptic Pappenheim staining of tumor/CAM border. BL2B95 cells show dark basophilic cytoplasm. CAM appears grayish blue with two blood vessels (bv) in the center of the picture. The tumor periphery is infiltrated by chick leukocytes, which are clearly visible due to their numerous reddish granules (arrows). Scale bar = 200 μm C: HE staining of tumors shows classical ‘starry sky’ appearance of BLs with tingible body macrophages (arrows and insert). Scale bar = 100 μm. D: Trichrome staining shows the small connective tissue proportion (green) of BL2B95 tumors. Scale bar = 100 μm. E: Ki67 immunohistochemical staining. More than 90% of the tumor cells are Ki67⁺. Insert shows negative control. Scale bar = 200 μm. F: Gomori silver staining of a tumor area with massive chick leukocyte infiltration; black fibres indicate agyrophilic fibres. Scale bar = 100 μm.