Five cell lines (21%) were sensitive to the MEK inhibitor PD0325901, and response was significantly associated with the presence of KRAS, HRAS or NRAS mutations (P=0.028) but not with the doubling time of cells (mean sensitive 30.76 ± 0.90h, mean resistant 39.88 ± 4.45h, MWU, P= 0.743).