Abstract
Tofacitinib is an oral Janus kinase inhibitor. Although it contributes to the induction and maintenance of clinical remission of patients with moderate-to-severe ulcerative colitis, various malignancies have been reported after the use of this small molecule. We report a rare case of biopsy-proven Kaposi sarcoma in a patient with complex biological-resistant ulcerative colitis after 2 years of treatment with tofacitinib. Kaposi sarcoma lesions spontaneously regressed after tofacitinib was discontinued. Given the concern of potential risk of malignancy associated with this agent, we believe that specialists should be aware of this rare but serious possible adverse event.