Follicular Dendritic Cell Sarcoma in a Patient With Adolescent‐Onset Crohn's Disease Exposed to Multiple Immunomodulator and Biologic Therapies

Children and adolescents with inflammatory bowel disease are often treated with immunomodulators (thiopurines, methotrexate) and biologics (anti-TNF, anti-integrin) for extended periods despite concerns about long-term safety. Here, we report a case of follicular dendritic cell sarcoma, a very rare malignancy, and the first reported presentation in a patient with inflammatory bowel disease exposed to infliximab, methotrexate, and vedolizumab. We review the key clinical features and diagnostic factors of this malignancy. The pathogenesis of follicular dendritic cell sarcoma is largely unknown, however, knock out of B-cell TNF in mice has been related to follicular dendritic cell dysregulation through its impact on NF-κB pathways and CXCL13 chemokines. It is unknown whether any relationship exists between this patient's diagnosis of Crohn's disease and therapeutic exposures to this rare malignancy. We document this case in the literature to raise awareness among other clinicians who may observe a similar case.