8 HNSCC and 3 pancreatic cell lines with different genetic backgrounds were treated with AT13387 (100nM) for 24 hours, Radiation (2, 4, 6, 8 Gy), or a combination of AT13387 and radiation. Cells were washed immediately after irradiation and incubated at 5% CO2 at 37 °C until detectable colonies (>50 cells) were observed in the untreated group. Colonies were fixed, stained using crystal violet solution, and counted. Enhancement ratios (ER) for the combination of radiation and AT13387 treatment relative to radiation alone were calculated. Genetic backgrounds and respective ER are tabulated (A). Representative survival curves are shown for UMSCC74B (B) and SCCVII (C) cells.