Recurrent ALK-negative anaplastic large T-cell lymphoma presenting as necrotizing vasculitis.

Anaplastic large cell lymphoma (ALCL) is a T-cell lymphoma histologically characterized by expression of CD30, a cell surface receptor present on activated T cells and B cells. ALCL may occur in a primary cutaneous form or as systemic ALCL with lymph node involvement. Anaplastic lymphoma kinase (ALK) is a tyrosine kinase that induces neoplastic transformation as a result of translocational fusion with an activating promoter. The presence of ALK can be used to distinguish between primary cutaneous ALCL and systemic nodal ALCL in certain cases. Primary cutaneous and systemic ALCL metastatic to the skin are histologically indistinguishable. "Leukemic vasculitis"--an uncommon finding in cases of cutaneous leukemia and even more exceptional in cutaneous lymphoma--refers to a pattern of vasculitis occurring as a direct result of infiltrating neoplastic cells. We report a fatal case of recurrent ALK-negative ALCL presenting as ulcerating skin lesions in a patient previously treated with the new anti-CD30 agent brentuximab vedotin. Biopsy revealed a necrotizing vasculitis resulting from the infiltration of neoplastic cells reminiscent of the patient's primary malignancy. We review the clinical and pathological findings of ALCL and present this case to highlight a subtle diagnostic clue in assessing recurrence of cutaneous lymphoma.