PIWIL4 and ductal breast carcinoma in situ: We observed progressive PIWIL2 and PIWIL4 downregulation with absence or very slight nuclear staining (HScore = 0–0.5) in atypical ductal hyperplasia (PIWIL2 (30%, n = 3) and PIWIL4 (20%, n = 2)) and ductal carcinoma in situ (PIWIL2 (40%, n = 4) and PIWIL4 (40%, n = 4)) (Figure S3).