Evaluation of Clinical Significance of Circulating Markers in Breast Cancer Patients Undergoing Herceptin Therapy

* Single Variate analysis will be performed to correlate variables such as tumour size, grade, stage, ER status, PR status and biopsy HER2 status with soluble HER2 levels. * Soluble HER2 levels will be analyzed as both a continuous and categorized variable. * The analysis will attempt to discern the relationship between soluble HER2 levels, HER2 positive circulating epithelial cell level and treatment response. * This will provide evidence of the effect various treatments have on HER2 levels. HER2 levels both in patients treated with Herceptin and those on other treatment protocols, will be related to clinical disease measures such as time to progression, time to failure, duration of response and duration of survival. * An initial model of the relationship between these factors and soluble HER2 as a marker will be established from the data.