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p53 wild-type is a tumor suppressor gene involved in DNA gene transcription or DNA repair mechanisms. When damage to DNA is unrepairable, p53 induces programmed cell death (apoptosis). The mutant p53 gene is the most frequent molecular alteration in human cancer, including breast cancer. Here, we analyzed the genetic alterations in p53 oncogene expression in 55 patients with breast cancer at different stages and in 8 normal women. We measured by ELISA assay the serum levels of p53 mutant protein and p53 antibodies. Immunohistochemistry and RT-PCR using specific p53 primers as well as mutation detection by DNA sequencing were also evaluated in breast tumor tissue. Serological p53 antibody analysis detected 0/8 (0%), 0/4 (0%) and 9/55 (16.36%) positive cases in normal women, in patients with benign breast disease and in breast carcinoma, respectively. We found positive p53 mutant in the sera of 0/8 (0.0%) normal women, 0/4 (0%) with benign breast disease and 29/55 (52.72%) with breast carcinoma. Immunohistochemistry evaluation was positive in 29/55 (52.73%) with mammary carcinoma and 0/4 (0%) with benign breast disease. A very good correlation between p53 mutant protein detected in serum and p53 accumulation by immunohistochemistry (83.3% positive in both assays) was found in this study. These data suggest that detection of mutated p53 could be a useful serological marker for diagnostic purposes. Introduction A variety of molecular genetic changes have been described in breast cancer. Oncogene and tumor suppressor gene alterations have been studied in an attempt to define the molecular correlation between prognosis and the clinical behavior of breast cancer phenotype (1). Among those, the p53 tumor suppressor gene has become the focus of intensive studies. The current and most powerful model of wild-type p53 function is one in which p53 monitors the genome for DNA damage (2). After treatment of cells with DNA damaging agents, p53 protein levels are increased by post-translational stabilization and can transactivate various genes that may be related to cell-cycle arrest or apoptosis (3). Arrest of cell-cycle progression following DNA damage is thought to represent a basic protective mechanism preventing replication of damaged template DNA. If damage is irreparable, the cell may be driven to apoptotic pathway, thus preventing replication of defective cells. Mutations in the p53 tumor suppressor gene are the most frequent known genetic alterations in all human cancers (4). Most of the biologically significant mutations impair the ability of p53 to participate in the maintenance of genomic stability. Consequently, tumors lacking normal p53 might be expected to be prone to deleterious mutations and to be more aggressive clinically. Many studies have examined the association between breast cancer prognosis and p53 protein expression in tumor cells (5-13). The use of immunohistochemistry (IHC) was based on the fact that missense mutations usually result in an increased half-life of the protein product and a consequent accumulation of the mutant p53 protein in the nucleus. Another different methodology is the detection of p53-specific antibodies, which explains the discrepant results for the p53accumulation in the same tumor type (5,8-12). Our purpose here was to study the relationship between p53 at protein and antibody levels and IHC in 55 cases of human breast tumor at different stages of the disease. These results revealed that the INTERNATIONAL JOURNAL OF ONCOLOGY 28: 995-1002, 2006 995 Mutant p53 protein in serum could be used as a molecular marker in human breast cancer G.A. BALOGH1,7, D.A. MAILO8, M.M. CORTE2,4, P. RONCORONI2,4, H. NARDI2-4, E. VINCENT4-6, D. MARTINEZ4,5, M.E. CAFASSO2, A. FRIZZA2,4, G. PONCE2, E. VINCENT4-6, E. BARUTTA2, P. LIZARRAGA2,4, G. LIZARRAGA2,4, C. MONTI2, E. PAOLILLO2,4, R. VINCENT4,6, R. QUATROQUIO4,5, C. GRIMI2,4,5, H. MATURI2,4-6, M. AIMALE4, C. SPINSANTI2, H. MONTERO2, J. SANTIAGO4,5, L. SHULMAN2, M. RIVADULLA2,4,5, M. MACHIAVELLI5, G. SALUM5, M.A. CUEVAS5, J. PICOLINI2, A. GENTILI1, R. GENTILI1 and J. MORDOH7 1Instituto de Analistas Clinicos Asociados (IACA); 2Sanatorio Privado del Sur; 3Hospital Interzonal Dr Jose Penna; 4Hospital Regional Español; 5Hospital Dr Leonidas Lucero; 6Hospital de la Asociacion Medica, Bahía Blanca; 7Instituto de Investigaciones Bioquimicas Luis F. Leloir, Fundación Campomar, Buenos Aires, Argentina; 8Fox Chase Cancer Center, Philadelphia, PA, USA Received October 25, 2005; Accepted December 2, 2005 _________________________________________ Correspondence to: Dr Gabriela Balogh, Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA 19111, USA E-mail: [email protected]