LAUSR

In vivo transplantation is the gold standard method for characterization of stem/progenitor cell self‐renewal, tissue regeneration, and tumorigenesis. The method requires an enriched population of stem cells that represent a small fraction of a given tissue. An enriched population of stem/progenitor cells increases the likelihood of engraftment and reduces the number of recipient animals needed for in vivo transplantation. Methods for mammosphere formation by mammary epithelial stem and progenitor cells have been widely adopted for enriching stem/progenitor cells, allowing researchers to study genetic and epigenetic properties, interaction with other cell types, and differentiation and oncogenic transformation. The generation of mammospheres is complex, however, involving many steps and requiring particular skill. Here we describe a detailed mammosphere protocol, including isolation and culture of human primary mammary epithelial stem/progenitor cells and their differentiation and passage in 3D organoid culture. We also describe a protocol for ex vivo culture of fresh human breast tissue for use in assays of clinical treatment. Step‐by‐step instructions detail tissue handling through passage of the stem/progenitor cell‐generated 3D organoids, which can be used to assess the properties, function, and neoplastic transformation of mammary stem/progenitor cells. © 2018 by John Wiley & Sons, Inc.