Rampalli et al. [9, 10] investigators found that SMAR1-related proteins in breast cancer are associated with HDAC2 by recruitment of HDAC2 Sin3 and retinoblastoma pocket proteins and inhibited the effects of cyclinD1 on cell cycle aspects by deacetylating the upstream region of cyclinD1 promoter on cyclin and found that the mechanism of action of oncogene SMAR1 is closely related to HDAC2. This evidence concerns the gene HDAC2 and breast cancer.