Beta-blockers, a common drug used in the management of heart disease and high blood pressure, may improve breast cancer survival and prevent metastases. This unique province-wide study will use cancer records, primary care drug data and tumour samples of breast cancer patients diagnosed in Northern Ireland, to determine if specific tumour characteristics in combination with beta-blocker therapy could improve cancer survival and reduce the risk of breast cancer recurrence. This study may provide a better indication of those patients whose tumours are most likely to progress and could ultimately, lead to a trial of beta blocker therapy in this patient setting.