Taken together our observations suggest that RASSF1A acts as an inhibitor of ERα driven breast cancer cell growth through a complex, hierarchically organized network that involves first suppression of the Hippo effector YAP1 and subsequent inhibition of AKT1, increased FOXO3A activity as well as the blockade of FOXM1 and ERα expression, thereby inducing growth arrest and senescence. This evidence concerns the gene YAP1 and breast cancer.