We sought to determine the mechanism by which loss of STAT5a phospho-residues affected breast cancer characteristics differentially by examining canonical STAT5a activity, and found 1) the canonical phosphorylation of pY694 is independent of either pS residue, and 2) there is nuclear localized STAT5a with loss of pY694, pS726, or pS780, with altered kinetics for translocation. The gene discussed is STAT5A; the disease is breast cancer.