Recently, Klf4 has been identified as a tumor-suppressor gene in colon, bladder, and gastric cancers.15, 16, 17, 18 Other studies have demonstrated that Klf4 is an oncogene in breast cancer and skin carcinoma.19,20 As a novel anti-hypertrophic transcriptional regulator, Klf4 mediates the HDACi-induced prevention of cardiac hypertrophy.21,22 Activated HDAC2 triggers hypertrophy by inhibiting the signal cascades of either Klf4 or inositol polyphosphate-5-phosphatase f (Inpp5f), indicating that Klf4 might be a specific target of certain HDACs. Here, KLF4 is linked to breast cancer.