CA215 is a tumor-associated antigen which originated from the generation of a monoclonal antibody, RP215, against cultured ovarian cancer cell extract in 1987. CA215 is predominantly expressed by cancer cells in both secreted and membrane-bound monomeric forms. Compared to normal immunoglobulin G, CA215 contains a significantly higher percentage of N-acetyl and N-glycoyl neuraminic acid (28% vs. 8%) in the O-linked glycans, but a lower content of N-acetylglucosamine (28% vs. 41%) in the N-linked ones. When each of the other known cancer biomarkers, such as AFP, CEA, CA 125, CA 19-9, CA 15-3, and Cyfra 21-1 were combined with CA215, it was generally demonstrated that much higher cancer detection rates were observed, as compared to the use of a single biomarker alone. Therefore, CA215, which consists mainly of cancerous immunoglobulins, was clearly demonstrated as a pan cancer biomarker for potential immunodiagnostic applications of human cancer.