In mice, PMA treatment increased 89Zr-PD-1 IgG uptake in EL4 lymphomas from 6.6 ± 1.6 to 13.9 ± 3.6%ID/g (P = 0.01), and tumor uptake closely correlated with PD-1 level (r = 0.771, P < 0.001). Here, PDCD1 is linked to lymphoma.