Factors affecting progression‐free survival (PFS) were investigated using data from three clinical trials (NCT00920790, NCT01626664, and NCT01173887) and one clinical study (UMIN000013294) conducted in patients with relapsed/refractory (R/R) or untreated CCR4‐positive aggressive adult T‐cell leukemia‐lymphoma (ATL) receiving mogamulizumab treatment. Here, CCR4 is linked to lymphoma.