Bcl2 expression is associated with centromere 17 alterations in luminal B breast cancer A. Matsionis * , I. Pavlenko, A. Petrov * Rostov Refional Institute, Dept. of Experimental Pathology, Rostov Regional Institute Objective: Bcl2 is an important established prognostic parameter in human breast cancer (BC) and chromosome 17 centromere (CEP17) copy number is proposed to be the same too. We evaluated Bcl2 expression in different BC's molecular subtypes in relation to increased CEP17 level (CEP17>3 per nucleus). Method: Immunohistochemistry for Bcl2 assessment and fluorescence in situ hybridization for detection of CEP17 alterations were used. Statistical analysis was performed with Fisher's exact test. Results: A total of 226 cases of female invasive BC's were analyzed (2010) (2011) . The tumour subtypes were as follows: luminal A (ER/PR+, Her2/neu-, Ki67<14 %) -118; luminal B (ER/PR+, Her2/neu-, Ki67>14 % or ER/PR+, Her2/neu+) -62; Her2/neu+(ER/PR-, Her2/neu+) -24; triple-negative -20. In our study group, Bcl2-cases were preferentially ER-in agreement with previous reports. However, 20,5 % tumours of luminal B subtype were Bcl2-too and all of them had increased CEP17 copy number (p= 0,0011, rφ=0,57). We therefore hypothesized that not only ER had influenced Bcl2 in luminal B BC but CEP17 alterations also. Conclusion: Centromere 17 alterations are associated to bcl2 downregulation in luminal B BC's. The mechanisms responsible for that remain to be established but the underlying cause could be promoter methylation or transcriptional repression.