Proliferation of NKTCL-derived cell lines in the presence of imatinib mesylate. SNK6, MEC04, and U937 cells were incubated for 72 hours in media with or without imatinib mesylate at concentrations of 1, 3, and 6 μM. Imatinib induced concentration-dependent growth inhibition of MEC04 cells. The effect on SNK6 was not significantly different from that observed on the myelomonocytic U937 cell line. The horizontal axis is the concentration of imatinib mesylate. The vertical axis is the percentage of control proliferation. Bars indicate the SEM of triplicate experiments.