ERBB2 and neoplasm: These studies were performed in NOD-SCID mice with s.c. tumors formed by inoculating tumor cells that homogeneously express HER2 and/or EGFR, but it would be useful to be able to engineer an experimental tumor xenograft model in mice composed of tumor cells that express HER2 or EGFR or have predefined receptor hetereogeneity by inoculating a mixed population of tumor cells expressing these two receptors.