Ductal carcinoma in situ (DCIS) refers to a stage of pre-invasive breast cancer where the growing tumor remains confined within the basement membrane (BM). The transition from DCIS to invasive breast cancer (IBC), occurring when cells breach the BM and invade the surrounding collagen-rich stroma, represents a critical step in breast cancer progression corresponding to a much worse prognosis. While increased matrix stiffness has been implicated in driving BM invasion, tissues are viscoelastic, and the impact of changes in viscoelasticity on initial invasion of the BM remains unknown. Here, we investigate the role of tissue viscoelasticity in the DCIS-to-IBC transition using a three-dimensional (3D) in vitro model of breast cancer progression. Organotypic mammary acini are formed, which develop an endogenous BM and are useful as a model of pre-invasive mammary epithelium. Spatial proteomics approaches are used to identify key similarities between the BM formed by the acini and the BM observed in vivo in DCIS. For 3D culture studies, acini are then encapsulated in alginate-based hydrogels with independently tunable stiffness and viscoelasticity. We evaluated how stiffness and viscoelasticity influence acini morphology, protrusive activity, and invasion-like behavior, finding that increased stiffness promotes invasion, but that matrix viscoelasticity mediates this effect, suggesting an impact on the malignant signaling in the cells. Our ongoing work is examining the changes in transcriptomics and seeks to identify key mechanotransduction elements mediating sensing of matrix viscoelasticity through the BM.
Alyafei et al. (2026) studied this question.