CD13-positive anaplastic large cell lymphoma of T-cell origin - A diagnostic and histogenetic problem - A case report and review of the literature

The expression of myelomonocytic-associated antigens in anaplastic large ce ll lymphomas (ALCLs), particularly those presenting in extranodal sites, ca n make their distinction from extramedullary myeloid cell tumors (EMCTs) or histiocytic tumors problematic. Yet, this distinction is clinically signif icant because of its therapeutic and prognostic implications. Herein, we de scribe a case of extranodal anaplastic lymphoma kinase-positive CD30-positi ve ALCL of T-cell origin in a 12-year-old boy, which was initially called a n EMCT because of the expression of CD13 and HLA-DR detected by flow cytome try and the absence of other T-cell-related surface markers. However, the d etection of cytoplasmic CD3 by flow cytometry prompted further studies. The tumor was composed of large cells with abundant slightly eosinophilic vacu olated cytoplasm and ovoid or reniform nuclei with a few small nucleoli. Us ing immunohistochemistry, the tumor was positive for CD45, CD30, CD45RO, an d CD43 with a strong cytoplasmic and nuclear anaplastic lymphoma kinase sta in. The tumor cells showed a T-cell clonal genotype. Electron microscopy re vealed no ultrastructural features of myelomonocytic or histiocytic origin. The patient responded well to the chemotherapy and was in complete remissi on for 10 months at the time of submission of this manuscript. Review of th e literature showed inconsistencies regarding the diagnosis, nomenclature, and, therefore, treatment and prognosis of these tumors. In addition, the C D13 expression in ALCL raises some histogenetic questions and may indicate origin from a pluripotent stem cell, misprogramming during malignant transf ormation, or a microenvironmental effect on lymphoid cell expression of sur face antigens. Therefore, ALCL should be considered in the differential dia gnosis of EMCTs or histiocytic tumors, particularly when surface marker lin eage assignment is ambiguous.