Diagnosis:
Anaplastic large cell lymphoma
• 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.