Recent studies that addressed comprehensive gene expression profiling in tumor-infiltrating Treg cells in colorectal, non-small-cell lung and breast cancers have revealed that CCR4 is not the optimal molecule for targeting tumor-infiltrating Treg cells; this is because CCR4 is predominantly expressed by eTreg cells in the peripheral blood rather compared to in the TME37,38. The gene discussed is CCR4; the disease is breast cancer.