A higher-power image of the lymph node reveals diffuse infiltration by large cells with abundant cytoplasm and large vesicular nuclei containing prominent (and often multiple) nucleoli. These cells are rather pleomorphic, some containing large round or elliptical nuclei, whereas others contain eccentric kidney-shaped or embryoid nuclei. The latter cells are known as "hallmark cells" and are characteristic for anaplastic large cell lymphoma (ALCL). The monomorphic cell population with smaller, hyperchromatic nuclei dispersed throughout the node represents non-malignant lymphocytes. (H & E 20×)