Mouse 4T1 is a 2-Amino-6-purinethiol resistant cell line selected from the 410.4 tumor without mulagen treatment. RMPI-1640 containing 10% serum is recommended for 4T1 cell expansion and these cells have a guaranteed average;50 additional population doubling levels when ciltured following the detailed protocol described below. RFP-expressing 4T1 cells are Zeocin resistant cells after transfected with lentiviruses expressing RFP under the control of CMV promotoers.