PET imaging is one of the fastest growing technologies in modern medicine. The introduction of PET imaging have truly revolutionized cancer medicine with the use of the glucose analogue FDG for cancer improved diagnosis, staging and treatment monitoring. Currently, more than 2 million FDG-PET scans are performed each year. However, in a number of the most common cancer types, e.g. prostate cancer, FDG-PET does not work and a clear unmet clinical need exists for new, innovative imaging technologies for improved diagnosis and tumor characterization.

In the case of solid tumors such as prostate and breast cancer, it is the ability of cancer cells to invade the surrounding tissues and to form distant metastases that leads to progression and poor prognosis. 

Numerous studies have documented that the serine-protease urokinase-type plasminogen activator (uPA) and its receptor (uPAR) are of special importance in cancer invasion and metastatic spread.

In line with this, high expression levels of uPAR in tumor tissues has been shown strongly associated with metastatic disease and thorough studies by immunohistochemistry and in situ hybridization have revealed low expression levels of uPAR in normal tissues compared with malignant cancer lesions. Together, these characteristics make uPAR an ideal target for cancer imaging for improved diagnosis, risk-stratification and treatment monitoring.