The immunotolerant MMTV-HER2/Neu (ERBB2) transgenic murine model (NeuN) originally characterized by Guy et al. [9], in which FVB/N strain mice express the non-transforming rat Neu cDNA under control by a mammary tissue-specific promoter, gives rise to spontaneous mammary tumors between 125 and 300 days. The gene discussed is RBFOX3; the disease is breast cancer.