ID1 and cancer: Afterward, BMPRI recruits and phosphorylates SMAD1/5/8, which translocate into the nucleus together with SMAD4 and promote the transcription of target genes such as inhibitor of DNA-binding 1 (ID1) and inhibitor of DNA-binding 3 (ID3).16 BMP signaling has been unveiled to maintain epithelial identity and attenuate the metastatic potential of breast cancer cells, which can be achieved by counteracting TGF-β signaling.17 Moreover, TGF-β is able to antagonize BMP signaling, indicating the imbalance between TGF-β and BMP may influence the EMT status and invasive abilities of cancer cells.18–20