In vivo characteristics of human and mouse breast tumor cell lines

Although two- and three-dimensional in vitro studies of breast tumor cell lines have increased our knowledge on tumor growth and metastasis formation, the complex in vivo microenvironment is not taken into consideration. The goal of our study was to illustrate the in vivo morphology and motility of widely used breast tumor cell lines. Intravital microscopy allows real-time visualization of individual cells inside tissues of living animals. We used this technique to study breast cancer migration in the complex orthotopic microenvironment. More specifically, we characterized cell morphology, cell-cell interactions, polarity and motility of mouse tumor cell lines 4T1 and mILC-1 and human tumor cell lines MDA-MB-231 and T47D. Almost all measured parameters were remarkably heterogeneous even between positions within the same tumor. Migrating tumor cells were circular in all tumor models, indicating predominantly amoeboid motility. This overview of the in vivo characteristics of mouse and human breast tumor cell lines illustrates their heterogeneity and complexity in real life, and additionally exemplifies caution should be taken to extrapolate in vitro assays of tumor invasiveness.