In contrast to the great advances in understanding of the functions of Piwi in germlines, their actions in cancer cells remain less clear. In particular, Piwi proteins have been asserted as oncoproteins, but little is known about how their oncogenic function is achieved in cancer cells. We conducted mass spectrometry-based quantitative proteomic analyses to monitor the proteome changes upon PIWIL1 downregulation in PDAC cell line.