PET receptor imaging in breast cancer

Most of the breast cancers overexpress certain receptors which have a role in development and progression of the disease. Receptors are also target for treatments. The most common receptors that are overexpressed in breast cancer cells are hormone receptors for estrogen (ER) and progesterone (PR) and human epidermal growth factor 2 (HER2) receptor. Various other receptors, such as receptors for androgen, somatostatin, chemokine, and gastrin-releasing peptide, have also been reported to be overexpressed in breast cancer. A number of PET radiotracers are available to image receptors in breast cancer, such as 18F-fluoroestradiol (FES) for estrogen receptors, 18F-fluorofuranyl norprogesterone (FFNP) for progesterone receptors, 89Zr- Trastuzumab for HER2 receptors, 18F-dihydrotestosterone for androgen receptors, 68Ga-Pentixafor for chemokine receptor CXCR4, various radiotracers for gastrin-releasing peptide receptor, and 68Ga-somatostatin analogs for somatostatin receptors. PET receptor imaging allows non-invasive and whole-body assessment of receptor status in the tumour (presence, distribution, heterogeneity, density, functionality, and binding availability of receptors). PET receptor imaging helps to detect tumour foci (staging and detecting recurrences), to evaluate receptor heterogeneity in primary and metastatic tumours and change in receptor status with time, to select patients for receptor targeting treatments as part of theranostics, to assess response to targeted treatments, to determine tumour behavior, and to predict survival and prognosis. In this review article, receptors and role of PET receptor imaging in breast cancer will be summarized.