ERBB2 and obesity due to melanocortin 4 receptor deficiency: Following the generation of obesity with 20 weeks of exposure to a HFD, GFP-labeled MTB/TAN primary tumor cells were orthotopically injected into lean and obese mice, and HER2/neu transgene expression was induced by doxycycline administration to drive primary tumor formation, and then doxycycline was withdrawn to induce HER2/neu downregulation and tumor regression to a nonpalpable state.