The scientists from The Scripps Research Institute (TSRI), University of Illinois, and the University of California (UC) have discovered two molecules of immune system that is believed to play a critical role in developing drug resistance in many tumors leading to breast cancer, especially in case of breast cancer that is estrogen driven. The immune molecules are interleukin 1 beta and tumor necrosis factor alpha. However, the researchers are still in search of the exact mechanism of these molecules by which it causes resistance.
Reference Link: http://www.scripps.edu/news/press/2017/20170320nettles.html