MTHFR and ductal breast carcinoma in situ: DMBA-induced tumors displayed ductal carcinoma in situ-like morphology and significant upregulation of fetal mammary developmental genes (<i>Tbx2</i> and <i>Tbx3</i>), the tumorigenesis-associated gene <i>Tp53</i>, and key epigenetic regulators (<i>Hdac1</i>, <i>Dnmt1</i>, and <i>Mthfr</i>).