Background: Anaplastic lymphoma kinase (ALK) is a tyrosine kinase inappropriately expressed in lymphoid tissue involved by CD30+ anaplastic large-cell lymphoma (ALCL) with the translocation t(2;5)(p23;q35)(, which juxtaposes the nucleophosmin gene (NPM) with that encoding ALK, resulting in a hybrid (NPM-ALK) message.
Patients and methods: A polyclonal antibody against residues of the kinase portion of NPM-ALK (designated anti-ALK 11) was tested for clinical utility in paraffin sections of 44 cases of pediatric large-cell lymphoma (LCL) and 17 additional lymphoma cases, by streptavidin-biotin-alkaline phosphatase method.
Results: Nineteen of 20 CD30+ cases (the majority exhibiting anaplastic morphology) labeled with anti-ALK 11, and 5/28 CD30- cases were also ALK+ (3 T cells, 1 null cell, and 1 B cell). Sixteen of 17 B-cell pediatric LCLs were negative, as were 6/6 cases of Hodgkin's disease and 7/7 cases of adult B-cell lymphoma. In pediatric LCLs with adequate follow-up (24/44 ALK+), there was no significant association between ALK expression and two-year event-free survival, similar to the finding reported previously for CD30 expression in these cases.
Conclusion: We conclude that the majority of pediatric CD30+ ALCLs show ALK overexpression, consistent with the presence of the t(2;5)-encoded NPM-ALK fusion, but that the clinical significance of this entity remains unproven.