We generated PyMT-induced mouse breast tumor cells by intraductal injection of lentivirus overexpressing PyMT into the mammary duct of wild type (WT) female FVB mice.31 Then, we transplanted PyMT-induced mouse breast tumor cells into WT and Hectd3−/− mice and examined the lungs 2 months after resection of orthotopic tumors. The gene discussed is HECTD3; the disease is breast neoplasm.