Senthil K. Muthuswamy1 and Joan S. Brugge2,3 1Laboratory of Cancer Biology and Genetics, Center for Cancer Research, National Cancer Institute, National Institutes of Health (NIH), Bethesda, Maryland 20894, USA 2Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA 3Ludwig Center at Harvard, Harvard Medical School Boston, Boston, Massachusetts 02115, USA Correspondence: senthil.muthuswamynih.gov; joan_bruggehms.harvard.edu

During the last decade, biomedical research has experienced a resurgence in the use of three-dimensional culture models for studies of normal and cancer biology. This resurgence has been driven by the development of models in which primary cells are grown in tissue-mimicking media and extracellular matrices to create organoid or organotypic cultures that more faithfully replicate the complex architecture and physiology of normal tissues and tumors. In addition, patient-derived tumor organoids preserve the three-dimensional organization and characteristics of the patient tumors ex vivo, becoming excellent preclinical models to supplement studies of tumor xenografts transplanted into immunocompromised mice. In this perspective, we provide an overview of how organoids are being used to investigate normal mammary biology and as preclinical models of breast cancer and discuss improvements that would enhance their utility and relevance to the field.