Anaplastic lymphoma kinase expression as a marker of malignancy. Application to a case of anaplastic large cell lymphoma with huge granulomatous reaction

Anaplastic large cell lymphoma (ALCL) shows a wide morphologic spectrum, including the occurrence of reactive components obscuring the neoplastic population. This makes its distinction from hyperimmune reaction difficult. The authors describe an ALCL in a girl wha had a tick bite 20 days prior to clinical presentation. She developed a huge epithelioid reaction (an unprecedented finding for this tumor). The diagnostic controversies were solved by applying the ALKc antibody against anaplastic large cell lymphoma kinase (ALK), in conjunction with reagents anti-nucleophosmin (NPM), which showed the typical staining pattern observed in ALCL carrying t(2;5). Comprised within the epithelioid component there were large anaplastic cells and small-medium sized atypical elements displaying strong nuclear and cytoplasmic positivity for ALK and NPM (N-terminal region). This pattern, never observed in normal lymphocytes, corresponds to the presence of the product of the hybrid gene NPM/ALK produced by t(2;5). Following the diagnosis, the patient - whose general conditions were critical - underwent aggressive chemotherapy, achieving complete remission.