The antigen recognized by RP215, CA215, can be detected in the shed media from a number of cultured cancer cells [2,5]. Therefore, Matrix-Assisted Laser Desorption/Ionization TimeOf-Flight Mass Spectrometry (MALDI-TOF MS) analysis was performed to determine the molecular identity of affinityisolated CA215 from the shed media of OC-3-VGH ovarian and C-33A cervical cancer cell lines [2,5]. Following tryptic digestion of CA215, the peptide fragments were subjected to analysis by MALDI-TOF MS. It was observed that as many as 50% of the peptide fragments derived from the shed media of cultured cancer cells were found to have a high degree of homology to antigen receptors, including immunoglobulins (42%) and T cell receptors (6%) expressed by cancer cells [5]. Many other different glycoproteins generally categorized as immunoglobulin superfamily proteins (IgSF) were also detected in such analyses [11].In view of the observation that the immunoactivity of the RP215-specific epitope in CA215 is destroyed by periodate treatments under mild conditions at neutral pH, it was assumed that the unique RP215 epitope is carbohydrate-associated [3]. Following extensive studies through glycopeptide mapping and glycosyl linkage analysis, it was suggested that the RP215-specific epitope may be associated with a simple O-linked glycan together with amino acid residues in the variable region of cancerous immunoglobulin heavy chains [12]. But this RP215-specific epitope is not found in immunoglobulins expressed by normal B cells [3].Since CA215 is cancer-associated, elevated levels of CA215 in the human circulation may indicate active growth/proliferation or metastasis of cancer cells in the human body [1,2,5,11,[13][14][15][16][17][18][19][20]. Immunoassays using RP215 as a unique substitute for antibodies against cancerous immunoglobulins have been established for the quantitative determination of serum levels of CA215 [1]. They have successfully been used to monitor CA215 levels in the human sera of patients confirmed or diagnosed with cancers of various tissue origins [21].Therefore, in this review, results of CA215 clinical evaluations are highlighted to demonstrate the potential applications of Abstract CA215 is a tumor-associated antigen which originated from the generation of a monoclonal antibody, RP215, against cultured ovarian cancer cell extract in 1987. To identify the molecular identity of CA215, MALDI-TOF MS studies were performed for affinity-isolated CA215 from shed medium of cultured OC-3-VGH ovarian cancer cells. RP215 was shown to react with a carbohydrate-associated epitope located mainly on the immunoglobulin heavy chains (designated in general as CA215) expressed by most cancer cells. By using RP215 as a probe, both sandwich and competitive immunoassays were formulated to determine the serum CA215 levels among patients diagnosed with known cancers of the lung, liver, colon, esophagus, ovary, breast, pancreas, cervix, and lymphocytes. When each of the other known cancer biomarkers, such as AFP, CEA, CA 125, CA 19-...
