As FGF2/FGFR2 axis has been implicated in activation and expansion of BM progenitors [21], coupled with the fact that FGF2 expression was found to be upregulated in ESCC [22, 23], we wonder if ESCC cells can stimulate the expansion of FGFR2+ fibrocyte progenitors in BM via secreting FGF2. Here, FGFR2 is linked to esophageal squamous cell carcinoma.