The combination of CCI-779 and cetuximab augments the sensitivity of cells to treatment with the mTOR inhibitor alone. All 10 cell lines were treated with increasing doses of CCI-779 (0.1-100 ng/ml) and long-term cell viability (7 days) was measured using the MTT assay. Additionally, CCI-779 treatment was combined with cetuximab at a low dose (0.1 μg/ml), at which the drug itself showed only little effect. In three EGFR-expressing, CCI-779 resistant cell lines the combination led to decreased cell viability (left graphs). Cell viability of sensitive cells could not further be decreased by the combination (three representative cell lines, right graphs). Survival fractions after drug treatment were calculated on the basis of the survival of non-treated cells.