Breast cancer organoids are able to overcome hNK cell cytotoxicity over time in 3D culture. (A and A′) Representative tumor organoids isolated from MMTV-PyMT (A) and C3(1)-Tag (A′) mice placed in 3D collagen I alone (top) or in coculture with hNK cells from FBV/n mice (bottom). Although hNK cells are initially able to limit tumor organoid invasion in both models at 24 h, by 36–48 h, tumor organoids are able to invade despite hNK cell activity. Scale bar, 50 µm.