FOXP3 and neoplasm: Nevertheless, the Treg cells within a tumor consist of very heterogeneous populations of either phenotypically stable suppressive/regulatory Tregs (forkhead transcription factor 3 - FoxP3++) and phenotypically unstable cells (FoxP3+/-), which could, under specific TME environment, switch their phenotype to effector Th1, Th2, Th17, or Tfh cells contributing to tumor elimination.