Fig. 6: CAM tumors possess typical characteristics of human breast cancers.

a MDA CAM tumor: H&E staining revealing a distinct small CAM tumor with clearly visible blood vessels and ill-defined borders, morphologically reminiscent of a small breast cancer lesion. Cancer cells within the CAM tumors were positive for CK18 and human mitochondria (Hu-Mito) and negative for human ERα. Anti-human CD34 staining revealed blood vessels lined by human EC and populated with nucleated avian erythrocytes suggesting functional anastomoses with the chicken embryo circulation. Faint staining for CD106 in the blood vessels points to EC that have been activated by factors secreted by the BCC. Lack of nuclear p63 (Supplementary Fig. 18a) and >40% positivity for Ki67 positivity is indicative of a more aggressive or metaplastic subtype of BC and corresponds to a grade G3. Scale bar: 100 µm. b MCF CAM tumor: H&E staining revealing cribriform structures in CAM tumor strongly resembling human breast cancer glands of a well or moderately differentiated breast cancer, with a necrotic center consistent with the absence of vasculature (negative for CD34). Positivity for CK22, Hu-Mito, ERα, and PR; and negative staining for Her2 (Supplementary Fig. 18c) confirm that the CAM tumors stem from human BCC and more specifically from hormone receptor (luminal) MCF-7 cells. Negative staining for CD106 confirms the avascular nature and the absence of stromal cell characteristics in MCF CAM tumor. The absence of myoepithelial cells (p63 -ve, Calponin -ve (Supplementary Fig. 18c)) and widespread positivity for Ki-67 (>90%) are indicative of an invasive BC phenotype corresponding to a grade of G2. Scale bar: 100 µm.