The PIWI-like RNA-mediated gene silencing 1 (PIWIL1) protein is an important member of the Argonaute protein family, and is highly expressed in germ cells; stem cells; a variety of cancer cells, including seminoma, gastric cancer, breast cancer, lung cancer, and colorectal cancer cells (1–6). The gene discussed is PIWIL1; the disease is breast carcinoma.