CD4 and cancer: Increasing numbers of Tregs have been reported in several human cancers, including not only breast cancer 27 but also lung,35 pancreas,20,36,37 and ovarian tumors.38 Tumor infiltration by Tregs has been shown to correlate significantly with worse prognosis among breast cancer patients.27 Foxp3 is a member of the forkhead box family of transcription factors and was initially thought to be a master regulatory gene for lineage commitment or development of CD4+CD25+ Tregs.19 Foxp3 remains the best single marker of Tregs.39