Hypocellular anaplastic large cell lymphoma mimicking inflammatory lesionsof lymph nodes

The subgroup of T/null-cell primary systemic anaplastic large cell lymphoma that expresses anaplastic lymphoma kinase (ALK) constitutes a distinctive clinicopathologic entity that exhibits a broad morphologic spectrum. The ex amples predominated by small cells or showing a mixed cell population can b e difficult to recognize as being neoplastic. We report four such cases wit h a remarkably hypocellular granulation tissue-like appearance, mimicking a n inflammatory or reparative process. All patients were young and presented with lymphadenopathy in multiple sites, The lymph node biopsies showed a h ypocellular appearance, with wide separation of the small to medium-sized l ymphoid cells by edematous or fibromyxoid stroma, There were interspersed s pindly neoplastic cells resembling myofibroblasts, sometimes forming short, sweeping fascicles, as well as histiocytes. Occasional large cells with at ypical nuclei were identified, The larger lymphoid cells tended to form cuf fs around the venules, In two cases, the capsule and fibrous trabeculae wer e markedly broadened with increased spindly cells, mimicking inflammatory p seudotumor of lymph node, Immunostaining showed dispersed and clustered CD3 0+ ALK+ cells, confirming a diagnosis of anaplastic large cell lymphoma. In conclusion, a diagnosis of hypocellular anaplastic large cell lymphoma req uires a high index of suspicion. The young age of the patients and the pres ence of perivascular cuffs of larger lymphoid cells should provide the stro ngest clues to the correct diagnosis.