Targeted radionuclide therapy for patients with CNS metastasis: overlooked potential?

Targeted radionuclide therapy is an emerging therapeutic concept for metastatic cancer that can be considered if a tumor can be delineated by nuclear medicine imaging and also targeted based on expression of a particular target (thera-nostics). This mode of treatment can also compete with or supplement conventional radiotherapy e.g., if MRI does not fully capture the extent of disease, including microscopic metastases. Targeted radionuclide therapy for patients with thyroid cancer, with certain somatostatin receptor 2-expressing tumors and with prostate-specific membrane antigen (PSMA)-expressing prostate cancer are approved, and numerous approaches of targeted radionuclide therapy for patients with metastatic cancer are in development (e.g. using fibroblast activation protein (FAP) as a target). Although brain metastases are rare in the cancers with approved targeted radionuclide therapies, there is no a priori reason to assume that such treatments would not be effective against brain metastases if the targets are expressed and not shielded by the blood brain barrier. Here, we discuss the current state of the art and opportunities of targeted radionuclide therapies for patients with brain and leptomeningeal metastases.