This paper describes mammary organoids with a basal‐in phenotype where the basement membrane is located on the interior surface of the organoid. A key materials consideration to induce this basal‐in phenotype is the use of a minimal gel scaffold that the epithelial cells self‐assemble around and encapsulate. When MDA‐MB‐231 breast cancer cells are co‐cultured with epithelial cells from day 0 under these conditions, cells self‐organize into patterns with distinct cancer cell populations both inside and at the periphery of the epithelial organoid. In another type of experiment, the robust formation of the basement membrane on the epithelial organoid interior enables convenient studies of MDA‐MB‐231 invasion in a tumor progression‐relevant direction relative to epithelial cell‐basement membrane positioning. That is, the study of cancer invasion through the epithelium first, followed by the basement membrane to the basal side, is realized in an experimentally convenient manner where the cancer cells are simply seeded on the outside of preformed organoids, and their invasion into the organoid is monitored. Interestingly, invasion is more prominent when tumor cells are added to day 7 organoids with less developed basement membranes compared to day 16 organoids with more defined ones.

BACKGROUND: The breast cancer microenvironment contains a variety of stromal cells that are widely implicated in worse patient outcomes. While many in vitro models of the breast tumor microenvironment have been published, only a small fraction of these feature adipocytes. Adipocytes are a cell type increasingly recognized to have complex functions in breast cancer. METHODS: In this review, we examine findings from recent examples of in vitro experiments modeling adipocytes within the local breast tumor microenvironment. RESULTS: Both two-dimensional and three-dimensional models of adipocytes in the breast tumor microenvironment are covered in this review and both have uncovered interesting phenomena related to breast tumor progression. CONCLUSION: Certain aspects of breast cancer and associated adipocyte biology: extracellular matrix effects, cell-cell contact, and physiological mass transport can only be examined with a three-dimensional culture platform. Opportunities remain for innovative improvements to be made to in vitro models that further increase what is known about adipocytes during breast cancer progression.