Progressive loss of epidermal growth factor receptor in a subpopulation of breast cancers: implications in target-directed therapeutics

Understanding the molecular etiology and heterogeneity of disease has a direct effect on cancer therapeutics. To identify novel molecular changes associated with breast cancer progression, we conducted phosphoproteomics of the MCF10AT model comprising isogenic, ErbB2- and ErbB3-positive, xenograft-derived cell lines that mimic different stages of breast cancer. Using in vitro animal model and clinical breast samples, our study revealed a marked reduction of epidermal growth factor receptor (EGFR) expression with breast cancer progression. Such diminution of EGFR expression was associated with increased resistance to Gefitinib/Iressa in vitro. Fluorescence in situ hybridization showed that loss of EGFR gene copy number was one of the key mechanisms behind the low/null expression of EGFR in clinical breast tumors. Statistical analysis on the immunohistochemistry data of EGFR expression from 93 matched normal and breast tumor samples showed that (a) diminished EGFR expression could. be detected as early as in the preneoplastic lesion (ductal carcinoma in situ) and this culminated in invasive carcinomas; (b) EGFR expression levels could distinguish between normal tissue versus carcinoma in situ and invasive carcinoma with high statistical significance (P

Reliability of tissue microarrays in detecting protein expression and gene amplification in breast cancer

Tissue microarrays allow high throughput molecular profiling of diagnostic or predictive markers in cancer specimens and rapid validation of novel potential candidates identified from genomic and proteomic analyses in a large number of tumor samples. To validate the use of tissue microarray technology for all the main biomarkers routinely used to decide breast cancer prognostication and postsurgical adjuvant therapy, we constructed a tissue microarray from 97 breast tumors, with a single 0.6 mm core per specimen. Inummostaining; of tissue microarray sections and conventional full sections of each tumor were performed using well-characterized prognostic markers (estrogen receptor ER, progesterone receptor PR and c-erbB2). The full section versus tissue microarray concordance for these stains was 97% for ER, 98% for PR, and 97% for c-erbB2, respectively, with a strong statistical association (kappa value more than 0.90). Fluorescence in situ hybridization analysis for HER-2/neu gene amplification from the single-core tissue microarray was technically successful in about 90% (87/97) of the cases, with a concordance of 95% compared with parallel analyses with the full sections. The correlation with other pathological parameters was not significantly different between full-section and array-based results. It is concluded that the constructed tissue microarray with a single core per specimen ensures full biological representativeness to identify the associations between biomarkers and clinicopathological parameters, with no significant associated sampling bias.