ERBB2 and neoplasm: Immunohistochemical analysis of the cell line showed that it overexpresses the R-RAS2 protein and, that like the freshly isolated mouse tumors [35], it is negative or low for estrogen receptor, progesterone receptor, and HER2 (ErbB2), and therefore can be considered triple-negative, in comparison with human tumor controls (Fig. 2a and b).