Category 2• Proliferative findings in stomach and renal tubules were considered preneoplastic changes• Hibernoma observed with tofacitinib• Address the potential for ‘off target’ tumors, despite the recognized malignancy risk from immunomodulation, for which rodent studies are considered poorly predictive• The effect of compound on prolactin signaling, as observed with the class, was not evaluated• Exposure associated with polyploidy at expected human therapeutic exposure unclear• Human cancer data described with tofacitinib considered not robust. Here, PRL is linked to cancer.