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Background: Metastasis represents an important adverse step in the progression of malignant breast cancer. Axillary lymph node status and the number of nodes involved are currently the most reliable predictors of survival in patients with metastatic disease. Because lymph node metastasis is associated with recurrence and decreased survival, it is important to understand molecular mechanisms underlying metastasis to develop more effective treatment strategies. This study used histologically directed MALDI-TOF tissue profiling to examine protein expression in primary breast carcinomas and surrounding histologically-normal tissues to better understand the processes of metastasis.

Methods: Matched (patient age and tumor size) primary breast carcinomas were obtained from 30 patients with axillary lymph node metastasis and 28 patients free from lymph node metastasis who were enrolled in the Clinical Breast Care Project at Walter Reed Army Medical Center. Following histological characterization on a hematoxylin and eosin stained slide, serial tissue sections were prepared and mounted on gold coated MALDI target plates for protein expression profiling. MALDI matrix was deposited as individual spots (200 microns in diameter) on the tissue sections in a histology directed manner to assay specific areas of primary tumor and adjacent histologically-normal tissue. Mass spectral data were then acquired from multiple sites of each tissue section by laser ablation and mass spectrometry analysis.

Results: In the resulting high quality mass spectral data, ~25 protein features were differentially expressed between primary tumors from node-positive patients and primary tumors from node-negative patients. Twenty-three protein features were highly expressed in the primary carcinomas of patients with lymph node metastasis, while two protein features were highly expressed in patients without lymph node metastasis. Several protein features represented proteins involved in calcium binding and regulation of macrophage function.

Discussion: Differences in protein expression between primary breast carcinomas from node positive compared to node negative patients suggest that primary tumors with metastatic capabilities express a unique set of proteins. Because metastatic breast cancer is currently an incurable disease that often responds only transiently to available treatment options, proteomic profiles may improve our understanding of biological processes involved in metastasis, allow molecular discrimination of patients with metastatic disease, and lead to development of novel therapeutics.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA