Treatment of lung, breast, and colon cancer cells with PTC-209 (potential compound a small-molecule Bmi-1 inhibitor) (1 and 2.5 μM) for 48 h showed no caspase-3 activation, but a decrease in the cell number below the seeding level suggests that PTC-209 reduces cellular viability probably through inhibition of cell proliferation and induction of cell death via a caspase-3-independent mechanism. This evidence concerns the gene CASP3 and malignant colon neoplasm.