This method was used to characterize the percent of HER2-positive and EGFR-positive cells ex vivo in s.c. tumor xenografts in NOD-SCID mice formed by the inoculation of 100% SK-OV-3 or MDA-MB-468 cells or a mixture of 30% SK-OV-3 cells and 70% MDA-MB-468 cells. This evidence concerns the gene ERBB2 and neoplasm.