Gene expression profiling of activated CTL and CD4+ T cells, as well as isolated tumor cells from T-cell–derived lymphomas, reveals that BCATc constitutes ~50% of the total BCAT expression in the non-malignant T cells, but this increases to ~60% in cutaneous T-cell lymphoma (CTLC), anaplastic large-cell lymphoma (ALCL) and angioimmunoblastic T-cell lymphoma (AITL). The gene discussed is CD4; the disease is anaplastic large cell lymphoma.