A total of 369 peripheral blood samples were collected from 123 de novo breast cancer patients (Tawam Hospital). Cancer tissues resected from those patients have been collected for mismatch repair proteins (MMR) expression analysis. Multiplex as well as single PCR reactions were conducted to amplify 5 loci on chromosomes 1, 2, 10 and 17 (Bat-26, Bat-40, MFD-41, TP53-Alu and MFD-28.CA). 84 patients out of the total cohort of 123 breast cancer patients tested positive, including 23 patients marked as high-positive MSI and 61 patients marked as low-positive MSI, 44 patients exhibited LOH in addition to MSI, while 39 patients tested negative to all markers and were reported to be microsatellite stable (MSS). Among the positive patients the following MSI and/or LOH incidence rates were detected; 40.47% positive for TP53-Alu (n=34), 32.14% positive for MFD-41 (n=27), 26.19% positive for MFD-28. CA (n=22), and 4.76% positive for Bat-26 (n=4). Higher occurrence of LOH has been noticed in TP53-Alu at allele no.397 and no. 404 which are located within a tumor suppressor gene (TP53). Immunohistochemistry results for detection of MMR proteins showed that 18% of the collected tissues tested negative for the hMSH-2 expression. Results showed a significant incidence of MSI and LOH in 3 out of the 5 tested markers (TP53-Alu, MFD-41 and MFD28.CA), and it was detected in higher frequency in TP53-Alu which may cause a loss of function of suppressor p53, which lead to a higher possibility of cancer formation. Periodic screening of the described markers and assessment of evident MSI and LOH of the relevant loci, especially on tumor suppressor genes will lead to an early detection of subsequent generation of secondary cancers.

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