In accordance with a previous model of diet-induced obesity in which MMTV-neu mice were chronically exposed to a HFD [35], primary tumorigenesis was similar in obese and lean mice with no differences in mean tumor growth rate (HFD-Obese 0.277 ± 0.100 cm3/day vs. HFD-Lean 0.251 ± 0.104 cm3/day vs. LFD 0.244 ± 0.071 cm3/day, p = 0.249) or mean total tumor burden (HFD-Obese 1786.1 ± 685.9 cm3 vs. HFD-Lean 1929.9 ± 798.7 cm3 vs. LFD 1805.4 ± 639.3 cm3, p = 0.606). The gene discussed is ERBB2; the disease is obesity due to melanocortin 4 receptor deficiency.