FGF2 and esophageal squamous cell carcinoma: In tumor-bearing mice, serum FGF2 increased steadily from baseline levels (11.84 ± 10.70 pg/mL) to the peak (104.72 ± 16.55 pg/mL) within 3 weeks after tumor implantation (P < 0.001), and declined immediately after tumor removal (Fig. 4C), confirming that serum FGF2 was mainly secreted by ESCC cells.