In the non-tumoral mammary glands of these mice, RRAS2 mRNA was expressed 3.2-fold more strongly than in Sox2-Cre— control mice, and a mean of 18.2-fold higher in the tumor tissue, suggesting a process of progressive upregulation of RRAS2 mRNA expression after the initiation event in mammary glands of knock-in mice (Fig. 1b). The gene discussed is RRAS2; the disease is neoplasm.