PDCD1 and metastatic melanoma: A recent study has shown that CD56, a marker associated with NK and NKT cells, is upregulated in peripheral blood of patients with metastatic melanoma who are responsive to anti‐PD‐1 immunotherapy.25 All these data suggest that NK cells play an important role in tumors, and our results also provided an evidence that NK cells with highly expressed PD‐1 may participate in tumor evasion of PTCL and chidamide could revitalize its antitumor activity.