MDA-MB-231 (HTB-26), MDA-MB-468 (HTB-132), MCF10A (CRL-10317), and MCF-7 (HTB-22) were purchased from ATCC in 2010 (MCF-7), 2012 (MDA-MB-468), and 2014 (MDA-MB-231 and MCF10A). Primary human fibroblast cells were kindly provided by Kathrin Scheckenbach, Düsseldorf, Germany in 2014. TMD231 cells were obtained from Dr. Harikrishna Nakshatri in 2009 and are a derivative of the MDA-MB-231 cell line (19 (link)). TMD231 cells were transduced with E2-Crimson lentiviral vector, p2CL7CR2wo, (TMD231-CR) for in vivo imaging as described (20 (link)). Upon receipt, cell stocks were cryopreserved at low passage. Authentication of molecular profiles was verified by short tandem repeat (STR) analysis (IDEXX BioResearch), and cells tested negative for mycoplasma. TMD231 cells were cultured in MEM-α (Gibco) supplemented with 10% FBS (Atlanta Biologicals) and 1% HEPES (Invitrogen). MDA-MB-231, MDA-MB-468, and primary human fibroblast cells were cultured in DMEM (Gibco) supplemented with 10% FBS (Atlanta Biologicals). MCF10A cells were cultured in Medium 171 (Gibco) supplemented with 1% MEGS (Invitrogen) and 0.1% cholera toxin (Sigma). All cells were cultured at 37°C with 5% CO2.