Here, we investigated EZH2 expression in ATLL biopsy specimens and compared this with other T-cell neoplasms, including T-lymphoblastic leukemia/lymphoma (T-ALL), anaplastic large cell lymphoma (ALCL), anaplastic lymphoma kinase (ALK)-positive (ALCL-ALK+), ALCL, ALK-negative (ALCL-ALK−), extranodal NK/T-cell lymphoma, nasal type (NK/TCL), peripheral T-cell lymphoma not otherwise specified (PTCL-NOS), angioimmunoblastic T-cell lymphoma (AITL), and T-cell prolymphocytic leukemia (T-PLL). Here, ALK is linked to T-cell prolymphocytic leukemia.