PCAT18 and acute lymphoblastic leukemia: Further, PCAT18, part of the T-ALL signature, is shown to be highly significantly correlated with the expression of the delta subunit of CD3 (CD3D), a well-known marker of T cell lineage [32] (Fig. 5B), confirming the specificity of this lncRNA to discriminate malignancy of T cells from acute leukemias of other blood cell types.