Although Becn1+/− mice show an increased susceptibility to tumor formation and an elevated incidence of multiple malignancies [23,24] crossings of Becn1+/− mice with mouse models of Erbb2- or PyMT-driven mammary tumorigenesis had no effect on tumor development ([60]; Vega-Rubín-de-Celis, unpublished data). The gene discussed is BECN1; the disease is neoplasm.