For the first time to our knowledge, we identified a generic expression pattern of inactivation of the PIWI–piRNA pathway present in 17 different malignant tumors, including IBCs, characterized by underexpression of the pi-RISCs catalytic and oncosuppressive effector proteins PIWIL2 and PIWIL4 and aberrant emergence of PIWIL1 and PIWIL3. Here, PIWIL4 is linked to cancer.