In 54 patients with PTCL who had circulating lymphoma cells in peripheral blood, the significant increase in PD-1 expression was a consistent finding and it differentiated AITL from other PTCL with high sensitivity and specificity (CD279-BV605 MFI; Mean ± SEM; 3079.0 ± 508.8 vs. 341.8 ± 54.17; p < 0.0001, AUC 0.986, Fig. 1l, m). This evidence concerns the gene PDCD1 and lymphoma.