Nuclear imaging of hormonal receptor status in breast cancer: a tool for guiding endocrine treatment and drug development.

Breast cancer is a commonly occurring disease in women and a major cause of morbidity and mortality. In the past decades, the development of medical endocrine therapies has led to a significant improvement in treatment outcome for this type of cancer. This therapy is targeting specific hormone receptors that are overexpressed by the tumor cells. In breast cancer, estrogen and progesterone receptors are important targets and therefore the receptor status of the tumor strongly determines treatment outcome. However, the receptor status can change during the course of the disease and consequently therapy resistance can occur. Therefore, insight in the current receptor status of the tumor is essential for optimal treatment. Nuclear imaging techniques like positron emission tomography (PET) and single photon emission computed tomography (SPECT), could provide the means to monitor the receptor status of tumors and the receptor occupancy by medical endocrine drugs in a non-invasive manner. Thus, these imaging techniques could offer a tool to guide therapy management in the individual patient. Nuclear imaging techniques for some of the relevant receptors for treatment of breast cancer are currently available. These imaging techniques could also aid the development of novel treatment strategies like modulation of hormone receptor expression. This review will address the role of hormone receptors in breast cancer treatment, the available nuclear imaging methods for monitoring the receptor status, the potential role of nuclear imaging in therapy management and drug development.