Abstract P2-06-10: Loss of Heterozygosity of an Intron 1 Polymorphic Sequence of Epidermal Growth Factor Receptor in Basal-Like Breast Cancer and Tumor-Adjacent Normal Tissue

Abstract

Abstract Background: Breast cancer (BC) is currently regarded as a heterogeneous disease classified, through gene expression analysis, into various molecular subtypes with different biological characteristics and clinical behaviour. Using a few protein biomarkers as estrogen, progesterone and HER2 receptors, BC subtypes can be divided in four main groups: luminal A, luminal B, HER2 and triple negative (TN). Triple negative BC are a heterogeneous subset of tumors grouped together on the basis of their lack of hormone receptor and HER2 expression. Although they demonstrate similarities in terms of pathological and molecular characteristics, they do not represent a uniform clinical entity since the expression of the basal cytokeratin (CK5) and EGFR may identify a subgroup, called basal-like, of very aggressive tumors encompassing about 10% of BC that display a particularly poor prognosis. Recently, in vitro and in vivo studies reported that the length of a CA Simple Sequence Repeat 1 (CASSRI) dinucleotides in the intron 1 of egfr was associated with the expression of EGFR. In addition, the loss of heterozigosity (LOH) within this region would also lead to altered receptor expression. In this study we aimed to determine the association between LOH and overexpression of EGFR in a series of basal-like BC and their in autologous uninvolved peritumoral tissues (PTT) in comparison to normal tissues (NT). Material and Methods: 35 TN BC, the correspondent PTT and the autologous NT were analyzed for EGFR, CK5 expression by immunohistochemistry (IHC) and for LOH using a fragment separation performed by capillary electrophoresis (ABI 3130 Applied Biosystem). The assessment of LOH on the three tissue substrates were evaluated comparing the peak area of the two alleles using the following equation: LOH score=T1XN2/T2XN1, where T is BC or PTT, N is normal tissue, 1 is the area under the peak corresponding to the shorter allele, and 2 to the longer allele. The result was significantly different from the ratio of the normal allele peak areas when the LOH score was < 0.79 (loss of the longer allele) or >1.27 (loss of the shorter allele). Results: Of the 35 TN BC, 29 (83%) expressed EGFR and/or CK5 and were defined basal-like BC. The remaining 6 (17%) cases, negative both for EGFR and CK5, were excluded from the study. Of the 16 EGFR positive basal-like BC, 10 (63%) showed LOH whereas of the 13 EGFR negative basal-like BC, only 3 (23%) showed LOH (p=0.03). Although in the majority basal-like BC with LOH (8/10; 80%) PTT displayed a genetic profile similar to NT and did not show LOH, interestingly, in 2 cases (20%) PTT is different from NT presenting LOH and expressing EGFR as the autologous BC. Conclusions: Our data indicate that LOH of CASSRI in the intron 1 of egfr is related to EGFR expression in basal-like BC. In addition, the evidence of LOH in PTT, denoting the occurrence of early molecular alterations in histologically normal tissues, could represent a potential biomarker with diagnostic/prognostic implications. Supported by AIRC Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P2-06-10.