STAT3 and breast cancer: There are also genes that has been known to have significant roles in other biological functions, such as breast cancer 1 (BRCA1), a well-studied breast cancer gene and signal transducer and activator of transcription 3 (STAT3), an intermediate component in signaling pathways for cytokines and growth factors such as interleukin-6 (IL-6) and vascular endothelial growth factor (VEGF).