Several primary bone marrow lymphoid malignancies should be included in the differential diagnosis, such as Hodgkin lymphoma (HL), Burkitt lymphoma (BL), follicular lymphoma (FL), diffuse large B-cell lymphoma (DLBCL), peripheral T-cell lymphoma not otherwise specified (PTCL-NOS), ALK-negative anaplastic large cell lymphoma (ALCL), lymphoplasmacytic lymphoma (LPL), hairy cell leukemia, acute lymphoblastic leukemia (ALL), and chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL). The gene discussed is ALK; the disease is anaplastic large cell lymphoma.