To this aim, first, we tried to estimate by fluorescence-activated cell sorting (FACS) the number of receptors per cell in cell suspensions obtained by dissociation of NIH/3T3 EGFR, NIH/3T3 HER2, NIH/3T3 EGFR/HER2 and SKOV-3 tumor xenografts. The gene discussed is ERBB2; the disease is neoplasm.