CD55 expression is higher in prostatic carcinoma,12 gastric adenocarcinoma13 and lymphoma,14 and is an independent factor of poor prognosis in colon15 and breast cancer.16, 17 Moreover, CD55 knockdown or CD55 low expression reduced tumorigenicity of prostatic adenocarcinoma and breast cancer in immunodeficient mice.12, 18 Interestingly, CD55 expression varies among monoclonal cell lines. This evidence concerns the gene CD55 and breast cancer.