The effect of Apo2L/TRAIL and gemcitabine alone and in combination (Tumor #2, day 5 of treatment). A. Many large glands are apparent in an untreated tumor. B, C. Tumors treated with Apo2L/TRAIL (B) or gemicitabine (C) contain fewer, smaller glands. D. Tumors treated with a combination of Apo2L/TRAIL and gemcitabine consist mainly of fibrotic tissue with foci of residual tumor cells (D, arrow). E-H. TUNEL assay. Few apoptotic cells are apparent in either the untreated (E) or gemcitabine treated (G) treated tumors. The Apo2L/TRAIL (F) and combination treated (H) tumors contain numerous cells undergoing apoptosis.