We have described a progesterone dependent recruitment of Brg1 and Brm to the MMTV promoter in breast cancer cells and have shown that yeast SWI/SNF can displace H2A/H2B dimers from MMTV recombinant nucleosomes [6], but the nature of the complex recruited in intact cells and its function in gene activation was not known. This evidence concerns the gene H2BC21 and breast cancer.