The significance of RAR activity in regulating the development of mammary adenocarcinomas was highlighted by a study by Kapumbati et al., where they showed that transplanting mammary epithelium from transgenic mice carrying a dominant negative RARα (RARαG303E) into the cleared fat pads of wild-type FVB mice resulted in the development of a metastatic mammary adenocarcinoma in one of the four transplanted glands 17 months post-transplantation [9]. The gene discussed is RARA; the disease is breast adenocarcinoma.