CXCR4 and breast cancer: In this study, probes were developed to target three very different cancer biomarkers: CXCR4, which is overexpressed in a wide variety of cancers and is associated with an aggressive, metastatic phenotype; CAV1, whose role in oncogenesis is heavily context-dependent; and the folate receptor, which is noted for frequent overexpression in ovarian and breast cancers.