Here we show that RASSF1A depends on LATS1 and LATS2 for the execution of its tumor-suppressor functions in ERα-driven breast cancer cells and suggests that the mutual interaction between RASSF1A and the Hippo-kinases LATS1 and LATS2 is important for the suppression of ERα+ breast cancers. This evidence concerns the gene ESR1 and breast cancer.