During the past 20 years, studies on the use of anti-Id Abs have focused on three main tumor Ags (i) the epithelial cell adhesion molecule (EpCAM) associated with colorectal cancer (CRC), also known as GA733, CO17-1A, KS-14, or KSA, (ii) the CD55, also known as decay-accelerating factor (DAF) involved in the regulation of the complement cascade, and (iii) the CEA known for its particularly strong expression in 95% of CRC, 70% of lung adenocarcinomas, and 50% of breast cancers. This evidence concerns the gene CD55 and breast carcinoma.