HDAC9 and breast cancer: Interestingly, even in HFD-fed PyMT transgenic mice that developed more advanced, poorly differentiated mammary tumors with increased HDAC activity and decreased expression of ERα and PR, oral administration of FTY720 not only suppressed development and progression of these spontaneous breast tumors, but also reduced HDAC activity in tumors and concomitantly induced expression of ERα and PR.