Breast cancer, the most common malignancy among women worldwide, is a heterogeneous disease, and it therefore has remarkably different biological characteristics and clinical behavior. Breast cancer has been divided into several different molecular subtypes based on the status of estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor 2 (HER2, also named as ErbB2) status. Her2 is a member of EGFR family of transmembrane tyrosine kinase-type receptors, and is involved in the activation of its downstream signaling cascades, which could promote cell proliferation, metastasis, and angiogenesis in tumors. In addition, Twist, a transcriptional factor has been shown to associate with ErbB2 signaling to increase the proliferation and the number of cells, and to induce epithelial-mesenchymal transition. Deregulated cell proliferation can result in hyperplasia and even malignancies. Actually, the proliferative or survival ability of cells can be measured by a variety of methods. Clonogenic assay and CCK8 assay can serve as useful tools to test whether the clonogenic survival ability of tumor cells can be enhanced or reduced upon stimulation of appropriate mitogenic signals or a given cancer therapy respectively. A colony is defined as a cluster of at least 50 cells that can often only be determined microscopically. Moreover, migration and invasion assay, in some degree, represents the potential for EMT promotion. Here, we introduce colony formation assay; CCK8 proliferation assay; soft agar; and migration and invasion assay using overexpression of ErbB2 and EGFR receptors as an example.
