Beside tyrosine residues, STAT3 could be serine phosphorylated, which is less well defined.7 Recent studies revealed that hypoxia leads to the activation of phospho‐STAT3‐Tyr, and STAT3 has been suggested to cooperate with HIF‐1α in VEGF activation under hypoxia in cancer cells.8 However, the colocalization and interaction of HIF‐1α/p‐STAT3‐Tyr/p‐STAT3‐Ser have yet to be investigated in breast cancer. This evidence concerns the gene STAT3 and cancer.