CD13-positive anaplastic large cell lymphoma of T-cell origin--a diagnostic and histogenetic problem

The expression of myelomonocytic-associated antigens in anaplastic large cell lymphomas (ALCLs), particularly those presenting in extranodal sites, can make their distinction from extramedullary myeloid cell tumors (EMCTs) or histiocytic tumors problematic. Yet, this distinction is clinically significant because of its therapeutic and prognostic implications. Herein, we describe a case of extranodal anaplastic lymphoma kinase-positive CD30-positive ALCL of T-cell origin in a 12-year-old boy, which was initially called an EMCT because of the expression of CD13 and HLA-DR detected by flow cytometry and the absence of other T-cell-related surface markers. However, the detection of cytoplasmic CD3 by flow cytometry prompted further studies. The tumor was composed of large cells with abundant slightly eosinophilic vacuolated cytoplasm and ovoid or reniform nuclei with a few small nucleoli. Using immunohistochemistry, the tumor was positive for CD45, CD30, CD45RO, and CD43 with a strong cytoplasmic and nuclear anaplastic lymphoma kinase stain. The tumor cells showed a T-cell clonal genotype. Electron microscopy revealed no ultrastructural features of myelomonocytic or histiocytic origin. The patient responded well to the chemotherapy and was in complete remission for 10 months at the time of submission of this manuscript. Review of the literature showed inconsistencies regarding the diagnosis, nomenclature, and, therefore, treatment and prognosis of these tumors. In addition, the CD13 expression in ALCL raises some histogenetic questions and may indicate origin from a pluripotent stem cell, misprogramming during malignant transformation, or a microenvironmental effect on lymphoid cell expression of surface antigens. Therefore, ALCL should be considered in the differential diagnosis of EMCTs or histiocytic tumors, particularly when surface marker lineage assignment is ambiguous.