ERBB2 and breast cancer: Both MMTV-Neu (Guy et al., 1992b) and MMTV-PyMT (Guy et al., 1992a) driven tumors (designated as Neu and PyMT tumors, respectively) have been well-characterized and used extensively to illuminate the roles of various oncogenic and tumor suppressive pathways that are relevant in Her2+ and other luminal breast cancers.