The breast cancer cell lines BT-20, BT-549, EFM-19, MCF-7, MDA-MB-157, MDA-MB-231, MDA-MB-361, MDA-MB-436, MDA-MB-468, T-47D were purchased from ATCC. NCI-H1703 (KRAS mutant vs wild-type), DLD-1 (KRAS G13D/wt) and DWT7 (del/wt) were previously described [16 (link)]. MCF-7, MDA-MB-157, MDA-MB-231, MDA-MB-361, MDA-MB-436, MDA-MB-468 were cultivated in DMEM, BT-549, EFM-19, T-47D, NCI-H1703 in RPMI, DLD-1 and DWT7 in McCoy media, and BT-20 in Eagle’s Minimum Essential Medium, supplemented with 10% BGS, 2mM glutamine, 100 U/ml penicillin and 10% HEPES (all Sigma-Aldrich). All cell lines were cultured in a humidified incubator at 37°C and 5% CO2 and passaged for < 3 months after thawing a given frozen vial. All cell lines were tested mycoplasma free prior to the experiments (MycoAlert, Lonza) and none was ever treated for mycoplasma throughout the experiments. For 3D culture of tumor spheres, ~10,000 cells/well were grown in black round bottom polystyrene ultra-low attachment microplates (Corning) using serum-free medium composed of DMEM (Sigma-Aldrich), basic fibroblast growth factor (bFGF), and EGF (20 ng/mL each, Sigma-Aldrich), and B27 supplement (Life Technologies).