The effect of Apo2L/TRAIL in combination with gemcitabine on an Apo2L/TRAIL sensitive and resistant pancreatic adenocarcinoma. A-D. Tumor #3; E-H. Tumor #4. Groups of tumor bearing mice were treated with: A&E- Controls, B&F- Apo2L/TRAIL alone, C&G- gemcitabine alone, D&H- Apo2L/TRAIL and gemcitabine in combination. Tumor #3 is sensitive to Apo2L/TRAIL alone (B; p = 0.006) while Tumor #4 is resistant to Apo2L/TRAIL (F). This differential sensitivity is also seen in the response to gemcitabine alone (C, p = 0.02, and G). The efficacy of Apo2L/TRAIL in combination with gemcitabine appears to be enhanced in Tumor #3 (D) and is significantly greater than either treatment alone in Tumor #4 (H; p = 0.008).