Although many types of mammalian cells divide in three-dimensional (3D) matrices, including metastatic cancer cells in the stromal/interstitial 3D extracellular matrix (ECM) and cancer cells at secondary metastatic sites, the vast majority of mammalian cell division research has been performed on cells cultured on two-dimensional (2D) substrates. Rounding up of cells into almost perfect spheres signifies and ensures the normal mitotic progression in mammalian cells on 2D substrates. However, our research employing a high-content live-cell imaging assay revealed a distinct, commonly occurring, 3D-specific mode of cell division, in which mesenchymal cells, which include fibroblast and invasive cancer cell lines, did not fully round up before mitosis took place (1). This distinct, 3D-specific mode of cell division is contributed synergistically by the capability of cells to form protrusions and the physical properties of the extracellular matrix (1). Our current research interest is to unravel the physical and molecular regulations of the mitotic rounding of mesenchymal-like cells in 3D matrix and their implications in cancer development and progression.