Construction and application of mammary and breast cancer organoids.

Mammary organoids and breast cancer organoids (BCOs) have become indispensable models for investigating mammary development, tumorigenesis, therapeutic response, and drug resistance. In this review, we summarize current strategies for constructing mammary organoids from adult mammary stem cells, pluripotent stem cells and immortalized mammary epithelial cell lines, and discuss how these models recapitulate key physiological processes. Additionally, we elaborate on four complementary approaches for building BCOs, including patient-derived tumor organoids (PDOs), gene-edited models, microenvironment reconstruction via multicellular co-culture, and organoid-on-a-chip platforms. Notably, we outline major applications of mammary organoids in developmental biology and translational fields, and emphasize the expanding roles of BCOs in living biobanks, mechanistic studies, high-throughput drug screening, personalized drug sensitivity testing, and immunotherapy response prediction. Finally, we point out key challenges including standardization, long-term genetic and phenotypic stability, vascularization, immune-context integration, and optimization of dynamic culture conditions, and propose directions to improve model fidelity and clinical utility.