The absence of CCR4 expression in PCGDTCLs hinders the use of the new anti-CCR4 monoclonal antibody mogamulizumab, which is now available for patients with MF/SS, but could also be useful in the differential diagnosis of PCGDTCL as MF is strongly CCR4 positive [5]. The gene discussed is CCR4; the disease is mycosis fungoides.