What Is a Radioligand?
A radioligand is a molecule made of two parts. One part is a targeting agent, a molecule designed to seek out and bind to a specific receptor or protein on the surface of cancer cells. The other part is a radioactive isotope that delivers therapeutic radiation once the molecule has attached to its target.
Think of it as a delivery system. The targeting agent acts like an address label, directing the radioactive payload to the right cells. Once it arrives, the radiation works locally, damaging the DNA of the cancer cells and limiting their ability to grow and divide.
The Theranostic Approach
The word theranostics combines “therapy” and “diagnostics.” The idea is that the same molecular target is used for both. First, a diagnostic scan is performed using a tracer that binds to the target protein. If the scan confirms that the cancer cells express the target, a therapeutic version of the same molecule, now carrying a treatment dose of radiation, is given.
This approach means the treatment is personalised. Only patients whose cancers show the target on the diagnostic scan are offered the therapy. It reduces the likelihood of treating patients who would not benefit and increases confidence that the therapy will reach the right cells.
Learn more about radioligand theranostics and the treatments available.
How the Radiation Works
The most commonly used therapeutic isotope in radioligand therapy is Lutetium-177 (Lu-177). It emits beta radiation, which has a range of only a few millimetres in tissue. This short range means the radiation is concentrated around the cancer cells the radioligand has bound to, with limited exposure to nearby healthy cells.
Lu-177 also emits a small amount of gamma radiation, which can be detected by imaging equipment. This allows doctors to perform scans after the therapy has been given to confirm that the radioligand has reached the cancer sites. It essentially provides a built-in verification step.
Examples of Radioligand Therapy in Use
Lu-177 PSMA: Targets PSMA on prostate cancer cells. A PSMA PET CT scan confirms eligibility, and then Lu-177 PSMA therapy delivers radiation to the cancer.
Lu-177 DOTATATE: Targets somatostatin receptors on neuroendocrine tumour cells. A Ga-68 DOTANOC PET CT scan is used for diagnosis, and Lu-177 DOTATATE is used for treatment.
Lu-177 FAPI: Targets fibroblast activation protein, which is expressed around many types of tumours. This is a newer application, and clinical research is ongoing.
Radioactive iodine: One of the oldest theranostic treatments. Thyroid cells naturally absorb iodine, so radioactive iodine can be used to both image and treat thyroid cancer.
Who Can Receive Radioligand Therapy?
Eligibility depends on several factors. The cancer must express the target protein, confirmed by a diagnostic scan. The patient must have adequate kidney function and blood cell counts to safely receive the treatment. Overall health and previous treatment history are also considered.
Radioligand therapy is currently used for specific cancer types, primarily advanced prostate cancer and neuroendocrine tumours. Research is expanding its applications to other cancers, and newer targets like FAPI and CAIX are being investigated.
What Patients Can Expect
The therapy is given as an intravenous infusion in a controlled setting. After the infusion, patients follow radiation safety precautions for a short period. Treatment is usually given in multiple cycles, with monitoring between each one.
Side effects vary depending on the specific therapy but can include fatigue, dry mouth, and temporary changes in blood counts. The nuclear medicine team provides detailed guidance before, during, and after treatment.
If you have questions about whether radioligand therapy could be relevant to your condition, discuss them with your treating oncologist or nuclear medicine physician.