Progression of tumor growth and metastasis. (Left) 4T1-1V cells (106) were introduced into mammary fat pads of normal female BALB/c mice and the animals were imaged on a weekly basis for six weeks. The animals were sacrificed at the end of the sixth week and organs and hind limbs were removed and imaged. Images for two representative animals are shown. (Top Right) Quantitation of light emission from primary tumor over the six week period. (Bottom Right) H&E staining of a section from a primary tumor illustrating a central area of necrosis infiltrated by leukocytes and neoplastic cells at the periphery. The neoplastic cells are poorly differentiated and characterized by the presence of large hyperchromatic nuclei and relatively small amount of cytoplasm. Identifiable neutrophils and mast cells that appear to be located extravascularly were observed in non-necrotic areas of the tissue.