Case Report: Malignant melanoma in a patient with Crohn's disease treated with ustekinumab.

The cornerstone of inflammatory bowel disease (IBD) treatment is immunomodulators. IBD patients are at increased risk of intestinal and extraintestinal malignancy. Ustekinumab is a fully humanized monoclonal anti-IL12/23 antibody with a good safety profile. Malignancies of breast, colon, head and neck, kidney, prostate, thyroid, and non-melanoma skin cancer have been reported among patients who received ustekinumab. We report the case of a 42-year-old Crohn's patient on long-term treatment with ustekinumab, who developed achromatic malignant melanoma. Crohn's was diagnosed at the age of 15, with upper and lower gastrointestinal involvement and was initially treated with azathioprine (2mg/kg for 4 years) and infliximab (5mg/kg for 6 weeks). Due to ileal obstruction, the patient underwent stricturoplasty and received adalimumab (40mg every other week) for two years. He then discontinued therapy and a year later underwent right hemicolectomy. Adalimumab was reinstituted (40mg every other week) and the patient remained in clinical remission for two years. His overall exposure to adalimumab was four years. Ustekinumab was initiated due to a relapse and after 3 years, an incident of scalp itching led to the diagnosis metastatic achromatic malignant melanoma bearing BRAF V600E mutation. He received targeted therapy with an initial good response. We aim to point out the risk of dermatologic malignancy in IBD patients on long-term immunosuppression and the lifelong and meticulous evaluation that is required.