HIF1A and cancer: Cancer cells also produce interleukin-6 (IL-6) to activate signal transducer and activator of transcription 3 (STAT3) to induce hypoxia-inducible factor-1alpha (HIF-1α), VEGF, and C-C motif ligand (CCL) 5 expression in lymphatic ECs (LECs) within premetastatic niches to promote metastasis [49].