ID1 and cancer: ID1, an inhibitor of differentiation and DNA binding-1 and a member of the helix-loop-helix (HLH) transcription factor family [9], has been known to play a crucial role in mammary epithelial cells and cancer cells by mediating diverse cellular functions, including inhibition of differentiation, delaying replicative senescence, promotion of cell proliferation, invasion and metastasis [10].