PD-L1 expression appears to vary widely amongst tumor cells, with low rates ranging from 0% [56] to 17% of cases [85], however one study has suggested that it is higher in refractory PTCL NOS, with 28% of rPTCL NOS cases being PD-L1+ [86]. The gene discussed is CD274; the disease is mature T-cell and NK-cell non-Hodgkin lymphoma.