Clinical Pathology: General Principles, Hematology & Coagulation, Immunology & Histocompatibility, Urinalysis, Body Fluids, Clinical Microscopy, Genetic Testing

446) A 7-year-old boy is taken to the pediatrician’s office by his parents with swollen lymph nodes in his neck and axillae and persistent fever over the past several weeks. In addition, the child complains that he often wakes during the night to find his pillow soaking wet from sweat. A section from an excisional biopsy of a lymph node is shown in the figure. No B-cell markers are positive when immunohistochemistry is performed. Which one of the following statements is true?

• Anaplastic large cell lymphomas (ALCL) are divided by the World Health Organization (WHO) into anaplastic lymphoma kinase (ALK)-positive and ALK-negative types.

• ALK expression is usually secondary to t(2;5) and is prognostically favorable.

• ALCL represents approximately 50% of childhood high-grade lymphomas. Diffuse lymphadenopathy and B symptoms are common.

• The neoplastic cells are CD30+ and approximately 90% have T-cell receptor (TCR) rearrangement. T-cell antigens are typically expressed, and when absent, the neoplasm is referred to as the null-cell type ALCL. This neoplasm is not driven by Epstein-Barr virus.

• If B-cell antigens are expressed on a morphologically similar neoplasm, the diagnosis of diffuse large B-cell lymphoma (DLBCL) is given, even in the presence of CD30 expression.

• Epithelial membrane antigen (EMA) is often expressed. Because the cells can attain a cohesive pattern of growth, this neoplasm can mimic a carcinoma; a cytokeratin (CK) stain can be helpful in distinguishing the two.

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