Although previous studies have demonstrated that the MOLF/EiJ x PyMT backcross population approximates the diversity of human breast cancer subtypes at the transcriptional level [8] [14,15], the MMTV-Myc tumors from which the Mvt1 and 6DT1 cell lines derived are thought to most closely resemble the human luminal subclasses [16]. The gene discussed is MYC; the disease is breast cancer.