Cells (8 × 103 per well) suspended in complete growth medium (Eagle’s basal medium supplemented with 10% fetal bovine serum (FBS) and 1% antibiotics) were added to 0.3% agar with different doses of DFMO in a top layer over a base layer of 0.6% agar with the same doses of DFMO. The cultures were maintained at 37 °C in a 5% CO2 incubator for 3 weeks and then colonies were counted under a microscope using the Image-Pro Plus software (v.6.0) program (Media Cybernetics, Inc. Rockville, MD).