Comparison of desmoplastic tumor stroma and normal stroma in breast cancer by MALDI-MS and histology directed protein profiling Free

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Background: Complex interactions among proteins in both tumor epithelium and its surrounding stroma are likely involved in promoting breast cancer development and progression. The progressive alteration of mammary epithelium during neoplastic transformation is accompanied by peritumoral fibroblast proliferation and compositional changes in the extracellular matrix (ECM) collectively referred to as desmoplastic tumor stroma (DTS). This stroma is histologically and biochemically different from normal stroma; however, its role in facilitating malignant growth is incompletely characterized. This study compared mass spectrometry profiles of normal breast stroma and DTS to identify proteins dysregulated in the tumor microenvironment during neoplastic progression.
 Methods: Human breast tumor specimens were obtained from 17 patients. Cases were selected which contained both areas of DTS and normal breast stroma in the frozen tissue samples. Two serial 12 µm sections were cut from each sample. One section was mounted onto a histology slide and stained with hematoxylin and eosin (H&E) and the adjacent section was thaw-mounted directly onto a gold-coated MALDI target plate. The H&E staining allowed the histological characterization and was a guide for the histology directed acoustic robotic matrix deposition on the tissue sections. Individual matrix spots of 200 µm in diameter were deposited on the DTS in the immediate vicinity of tumor areas and also on the normal stroma surrounding normal lobular units. Profile spectra were acquired from the marked areas across the sections by matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS). Statistical comparisons by Significance Analysis of Microarrays (SAM) using a minimum 2 fold-change and false discovery rate <1% was used to identify the differentially expressed proteins.
 Results: From the identifiable protein features of the mass spectra obtained, a set of nine proteins showed differential expression between the two groups which reached statistical significance. Eight proteins showed greater expression (>2-fold) in the desmoplastic tumor stroma and one protein showed greater expression in the normal stroma.
 Discussion: Recent findings underscore that the stromal-epithelial interface is a critical mediator of oncogenic potential and suggest that the effectiveness of breast cancer therapies directed against ER, EGFR or microvessels might ultimately depend on the properties of the surrounding DTS. The identification of intermediary proteins in these signaling pathways and other undiscovered pathways by the comparative study of protein expression in normal stroma and DTS may ultimately lead to the manipulation of these pathways for the prevention and treatment of breast cancer. Identification of the differentially expressed proteins is currently underway.