This study describes the development of a quantitative tumour proteomics methodology and its implementation to study a type of breast cancer known as triple negative. The . quantitative proteomics technique deyeloped in the course of the study uses label-free mass spectrometry and size-based protein separation combined with bioinformatics and allows unlimited number of tumour samples to be analysed and compared in a highly automated manner. The methodology was applied to identify candidate biomarkers and drug targets for potential new therapies for triple-negative breast cancer. Another set of experiments builds on some of these findings, the surprising overexpression of interferon gamma-regulated genes in the lymph node-metastatic group of the analysed tumours, and examines the effect of interferon gamma on the water soluble and membrane-bound proteins of the metastatic triplenegative breast cancer cell line MOA MB231. A number of soluble and membrane proteins are identified to be affected by interferon gamma - notably proteins known to be involved in metastasis and calcium ion binding and calcium -regulated proteins. In a parallel line of investigation the effect of one of the proteins found to be overexpressed in lymph nodemetastatic triple-negative tumours, (074, on the proteome and phosphoproteome of another breast cancer cell line, M(F7 is examined. Overexpression of (074 is shown to cause sustai[1ed activation of the ERK1/2 module and also phosphorylation of the focal adhesion kinases FAK1/2. The activation of ERK1/2 is then validated by immunochemical techniques and shown to be synergistically regulated by calcium ions since calcium and (074 overexpression result in the strongest activation of the mitogen-activated protein kinase module. Thus, the quantitative phosphoproteomics studies again pinpoint calcium homeostasis, together with inflammation and mechanisms that are regulated by cytokines as important factors that contribute to the aggressiveness of triple-negative breast cancer.