So far no effective therapeutic has been developed for the FDA-approved treatment of ovarian cancer patients. Recently we provided the first evidence indicating that an old antibiotic (antiparasitic drug) called Ivermectin suppresses the growth of a variety of human ovarian cancer cell lines in vitro by inactivating the oncogenic kinase PAK1 somehow (Hashimoto H, et al. Drug Discov Ther. 2009;3:243-246). This kinase is now known to be essential for the growth of more than 70% of all human cancers including breast, prostate, pancreatic, colon, gastric, lung, cervical, thyroid cancers as well as hepatoma, glioma, melanoma, MM (multiple myeloma) and NF (neurofibromatosis) tumors. In this study, using the cell-permeable PAK1-inactivating peptide TAT-PAK18 which blocks the essential PAK1-PIX interaction, we examined the relationship between the sensitivity of ovarian cancer cell lines to this anti-PAK1 peptide and the protein expression/autophosphorylation levels of PAK1 in these cell lines, and found that the more PAK1 is abnormally activated (autophosporylated at Thr 423), the more their growth is sensitive to this peptide, regardless of their PAK1 expression levels. This observation provides the first direct evidence that ovarian cancers also belong to the PAK1-dependent cancers which represent more than 70% of all human cancers, suggesting that anti-PAK1 drugs would be effective therapeutics for ovarian cancers.