An isolated atypical cutaneous infiltrate may represent aleukemic CMS and should prompt a search for other extramedullary sites of involvement. Immunohistochemistry, molecular and cytogenetic studies can help differentiate aleukemic CMS from benign and malignant, monocytic and histiocytic mimickers, and may potentially indicate therapy and prognosis.

Vascular anomalies may be appropriately classified into two broad categories, vascular tumors and vascular malformations, which are distinguished by the presence of cellular proliferation in contrast to aberrations in morphogenesis, respectively. This system of classification is based upon histological features that may in large part be differentiating, but nevertheless, may show morphological overlap. Advances in immunophenotyping allow for more precise diagnoses as well as further delineation of cell origins. In the discussion, we present the clinical, histological, and, when applicable, the immunophenotypic presentation of vascular anomalies commonly seen in infancy and early childhood.

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.

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