Tumor cell migration into primary tumors can be directly assessed by multiphoton microscopy on animals whose tumors are labeled with green fluorescent protein (GFP) (Condeelis and Segall 2003). Breast carcinoma cells are characterized by an amoeboid migration behavior. These cells often move linearly and require extracellular matrix (ECM) fibers. Some of these ECM fibers form along blood vessels and serve as a pathway for carcinoma cell migration mediated by chemotactic agents.
These chemotactic substances are produced by blood vessels and other cell types. Epidermal growth factor receptor expression (EGFRE) directly correlates with the ability of mammary carcinoma cells to invade and metastasize. Therefore, EGF is thought to be a key chemotactic agent mediating breast cancer invasion. Once the carcinoma cells reach the blood vessels through chemotactic migration, they flow with the bloodstream to distant organs, where they then invade and form metastases (Wang, Wyckoff et al., 2002, Wang, Goswami et al., 2004).