Axillary lymph node (ALN) metastasis is a key step of tumor progression in breast cancer and is associated with an unfavorable prognosis. However, the mechanisms of this process are not well understood. Proteomic technologies have led to identification of specific protein markers and a better understanding of the cellular processes. To explore this, differential protein expression was analyzed between node-positive breast carcinoma and node-negative breast carcinoma (11 samples) and between primary breast carcinoma and matched metastatic ALN (five pairs) using a combination of 2D-SDS-PAGE and LC-MC/MS. Of the total 678 protein spots, 19 proteins were up-regulated and 3 proteins were down-regulated in node-positive breast carcinomas compared to node-negative breast carcinomas. Four up-regulated proteins were identified, namely annexin 5, carbonic anhydrase I, peroxiredoxin 6 and proteasome α2 subunit. For proteins altered in metastatic ALN compared to primary tumors, 6 of 14 up-regulated proteins were identified: heat shock 70 kDa protein 5, protein disulfide isomerase, prolyl 4-hydroxylase β subunit precursor, lactate dehydrogenase B, triosephosphate isomerase 1 and β-tubulin and 5 of 23 down-regulated proteins were identified including 90 kDa heat shock protein, chain A apo-human serum transferrin, chain A α1-antitrypsin, enolase 1 and macrophage migration inhibitory factor. Immunohistochemistry showed stronger immunostaining for β-tubulin in metastatic ALN compared to primary breast tumor. All of the identified proteins function in various processes involved in cell survival and growth. Our results suggest that these processes are critical for tumor progression and metastasis and the proteins identified could be candidate markers of clinical usefulness.

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