(a). Temporal changes in the tumor pO2, and (b). Tumor volume in the control (diamond, N = 6–9), conventional chemotherapy (square, 150 mg/kg gemcitabine, d1, d8, d15, N = 7–9) and metronomic chemotherapy (triangle, 25 mg/kg and circle, 15 mg/kg gemcitabine on dl, d3, d5 each week for 3 weeks, N = 12–18). $, p<0.05 day 1 vs. d3–d22, control; &, p<0.05 day 1 vs. d3–d22, 150 mg/kg gemcitabine; #, p<0.05 day 1 vs. d3–d22, 15 mg/kg gemcitabine; †, p<0.05 150 mg/kg gemcitabine vs. control; *, p<0.05 25 mg/kg gemcitabine vs. control; ‡, p<0.05 15 mg/kg gemcitabine vs. control