Using female nonobese diabetic severe combined immunodeficiency gamma (NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ) (NSG) immunodeficient inbred laboratory mice as the model, we assessed human breast tumor detection and development in response to MDMX or MDM2 knockdown. The gene discussed is MDM4; the disease is breast neoplasm.