According to the Canadian Cancer Statistics, there will be approximately 187 600 new cases of cancer in 2013. Although new treatments are constantly being developed, some of them target specific molecules that are present in only a minority of patients. Thus, not all patients are suitable for these treatments. This underlies the need to have new methods of diagnosing and profiling cancer patients to identify who will benefit from novel treatments. Herein, we propose targeting Carbonic Anhydrase IX (CA-IX) for the diagnosis and treatment of aggressive breast cancers. CA-IX is a protein expressed on cancer cells that grow in an unfavourable environment and lack oxygen. CA-IX facilitates cell survival in the unfavourable environment associated with aggressive cancers, and helps cells survive when they spread outside the primary tumour. Clinically, CA-IX has been associated with lower patient survival. In this project, we will assess the feasibility of using positron emission topography (PET) as an imaging modality to detect CA-IX. PET is a non-invasive imaging procedure that can be used to measure the biochemistry of lesions and provide functional information to classify them as benign or malignant. PET can also be used to assess a patient's response to different treatment regimens. If successful, this research will provide a platform to detect CA-IX in breast cancers and allow physicians to determine if patients' tumours express sufficiently high levels of CA-IX to make them candidates for treatments targeting this protein.