Systemic and primary cutaneous anaplastic large cell lymphoma: Clinical features, morphological spectrum, and immunohistochemical profile

BACKGROUND: T-cell lymphomas with anaplastic morphology typically comprise of anaplastic lymphoma kinase positive, anaplastic large cell lymphoma (ALK+ ALCL), ALK-negative ALCL (ALK- ALCL), and primary cutaneous ALCL (PC-ALCL). However, other entities such as diffuse large B-cell lymphoma, peripheral T-cell lymphoma, Hodgkin lymphoma, and undifferentiated carcinoma can also show similar anaplastic features. AIMS: To study the clinical features and histological spectrum of ALCL and emphasize the role of immunohistochemistry (IHC) in their diagnosis and categorization. SETTING AND DESIGN: Eight cases of ALCL diagnosed over a period of 4 years were selected for the study. MATERIALS AND METHODS: Histopathological review and IHC was performed on all cases. Two ALK+ ALCL cases were tested by fluorescent in situ hybridization (FISH) for t(2;5)(p23;q35). RESULTS: There were four cases of ALK+ ALCL and two each of ALK- ALCL and PC-ALCL. Histologically, all the subtypes showed pleomorphic and “hallmark” cells with strong CD30 expression and variable loss of T-cell antigens. One case of PC-ALCL was leukocyte common antigen (LCA) negative. Epithelial membrane antigen was positive in all the six systemic ALCL cases. Two cases tested for t(2;5)(p23;q35) by FISH were positive. CONCLUSIONS: Diagnosis of ALCL is based on recognizing the key morphological features, especially the presence of “hallmark” cells. IHC is essential for confirmation of diagnosis and excluding other malignancies with anaplastic morphology. The inclusion of CD30 in the initial IHC panel will help identify LCA negative cases and avoid misdiagnosis.