CXCR4 and ovarian cancer: Besides the upstream signaling of HIF-1α, the downstream effectors of HIF-1α might also be involved in the ovarian cancer malignancy, namely, C-X-C motif chemokine ligand 12 (CXCL12) and C-X-C motif chemokine receptor 4 (CXCR4) (Takano et al. 2014; Scala et al. 2020).