PIWIL2 and atypical ductal hyperplasia: PIWIL2 and PIWIL4 were downregulated in pre-invasive breast lesions such as atypical ductal hyperplasia (PIWIL2 (30%) and PIWIL4 (20%)) and ductal carcinoma in situ (PIWIL2 (40%) and PIWIL4 (40%)).