As breast cancer is not a single disease entity, all these tumour models do not cover breast cancer in general, but rather model individual aspects of mammary gland carcinogenesis or breast cancer (e.g., those expressing different hormone receptors (ERs, progesterone receptors [PRs]) and Human Epidermal Growth Factor Receptor 2 [HER2]). The gene discussed is NR4A1; the disease is breast carcinoma.