Complete remission of relapsed ATXN2L::JAK2 fusion positive anaplastic large cell lymphoma following ruxolitinib monotherapy in a child.

Anaplastic large cell lymphoma (ALCL) is a rare form of mature T cell lymphoma in children, particularly the anaplastic large cell kinase (ALK) negative subtype. Despite frontline treatment advances, there is no standard approach to treat relapsed disease and prognosis remains poor. Recently, JAK/STAT activating mutations have been implicated in the pathogenesis of ALK-negative ALCL in adults, but the oncogenic drivers of this disease in children are not well characterized. Herein, we describe a case of a 13 year-old boy with early systemic relapse of ALK-negative ALCL harboring a rare ATXN2L::JAK2 fusion, who achieved complete remission with ruxolitinib monotherapy. Consolidative allogeneic hematopoietic stem cell transplant HSCT then lead to long-term remission. This case underscores the critical role of comprehensive genomic profiling for rare histologies and supports the potential utility of JAK/STAT pathway inhibitors in select patients with ALK-negative ALCL.