STAT3 and rheumatoid arthritis: For example, tofacitinib (an oral Janus kinase 3 [JAK3] tyrosine kinase inhibitor, Pfizer Inc.), which inhibits STAT3 phosphorylation, was approved by the US Food and Drug Administration (FDA) for the treatment of patients with RA who are unresponsive to disease-modifying antirheumatic drug (DMARD) therapy10.