The diagnosis of MZL and LPL require exclusion of follicular lymphoma (by negative expression of CD10, Bcl-6, and FMC7), chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL, by negative expression of CD5, CD23, LEF1, and CD200), and mantle cell lymphoma (MCL, by negative expression of CD5, Bcl-1/cyclin D1, and SOX11). The gene discussed is CD200; the disease is mantle cell lymphoma.