In order to determine whether PIWI proteins are also deregulated at an early step of breast carcinogenesis, we analyzed PIWIL1-2-3-4 expression by IHC in a series of 10 normal breast tissues and 20 pre-invasive neoplastic lesions, including atypical ductal hyperplasia (n = 10) and ductal carcinoma in situ (n = 10). Here, PIWIL1 is linked to ductal breast carcinoma in situ.