Immunohistochemical staining for CD44, ALDH1A3, and c-MET (a) and image analysis quantification of protein expression (b) after radiation (RT) treatment. CD44 was mainly associated with the cell surface and tended to stain cells in the outer layers of the tumor islands; its expression decreased after radiation but recovered between days 12 and 21. ALDH1A3 staining was cytoplasmic and showed a diffuse pattern throughout the tumors. After irradiation ALDH1A3 increased to a maximum on day 7 and remained elevated for the period of observation. In some areas cells became more intensely stained with ALDH1A3 after irradiation. c-MET showed a staining pattern which was similar to ALDH1A3 being diffuse and cytoplasmic. The levels of c-MET increased at day 4 and reached a maximum at day 12 after which they declined rapidly to control levels (×20).