We describe here for the first time tumor xenografts in NOD-SCID mice with predefined receptor heterogeneity formed by the s.c. inoculation of mixtures of HER2-positive/EGFR-negative SK-OV-3 human ovarian cancer cells and EGFR-positive/HER2-negative MDA-MB-468 human BC cells. This evidence concerns the gene EGFR and breast cancer.