ESR1 and breast cancer: In addition to antiestrogens in estrogen receptor- (ER-) positive breast cancers, expression of Bcl-2 or Bcl-xL can be downregulated in specific types of cancer and leukemia cells by small molecule drugs that modulate the activity of retinoic acid receptors (RAR), retinoid X receptors (RXR), PPAR, vitamin D receptors (VDR), and certain other members of the SRTF superfamily.