Therapy + Diagnostics = Theranostics
The word Theranostics includes two concepts- therapy and diagnosis. Theranostics is a combination of diagnosis, targeted therapy and monitoring of therapy outcomes through the capabilities of modern medicine.
What is theranostics?
Theranostics is the term used to describe the combination of using one radioactive drug to identify (diagnose) and a second radioactive drug to deliver therapy to treat the primary tumor and metastasis. Theranostics is an evolving new approach to cancer treatment that may be appropriate for some patients who have not responded to other therapies. It is a two-pronged approach to diagnosing and treating cancer using radioactive tracers. Radioindicators are compounds made up of radiation and chemicals that selectively bind to a specific target in the body.
How do theranostic radioactive indicators work?
The radioactive tracer consists of two parts: one half is the biological side that passes through the blood to bind to a unique, specific target - in this case, a type of cancer cell. The other half is the radioactive component. During the diagnostic scan, this radioactive component emits a small amount of radiation, allowing pictures to be taken of the cancer cells on which the radioactive indicator has attached itself. During treatment, the biological side is almost identical, but the radioactive component is a different, more powerful type of radiation that kills the cancer.
During the diagnostic and treatment procedures, the biological side has to connect with this exact target on the tumor cells. Since most other healthy cells do not have this target, radioactive tracers do not attach to them.
Who is eligible for theranostic procedures?
Theranostics are an option for cancers that do not respond well to established systemic therapies such as conventional chemotherapy. If they stop working, the patient may be a candidate for theranostics. First, a PET scan is performed to determine if the tumor can be targeted by markers. If the answer is yes and the tumor is widespread, then the patient is a suitable candidate. If the tumor is not widespread, selective treatments such as surgery, external irradiation, or embolization may be more effective.
What types of cancer can be treated with theranostics?
One of the oldest, tried and true theranostics that is still commonly used is a pair of radioactive iodine markers for thyroid cancer. This procedure has been performed successfully for decades and remains an important part of thyroid cancer treatment options. Unlike other theranostic procedures that are administered intravenously, this one is given as a pill or liquid.
Modern theranostic medicine uses complex biochemistry to treat cancers such as:
- Neuroendocrine cancer. Lu 177 dotatate (Lutathera) has revolutionized the way neuroendocrine tumors, specifically carcinoids, are treated. Lu 177 dotatate targets somatostatin receptors on tumor cells.
- Prostate cancer. Lu 177 vipivotide tetraxetan PSMA (Pluvicto) treats patients with resistant prostate cancer who have already had androgen receptor pathway inhibition and taxane-based chemotherapy. Patients receive an infusion every six weeks for a total of six treatments.
- Pheochromocytoma and paraganglioma in adults; pediatric neuroblastoma. I131-iobenguane/MIBG (Azedra) is used to treat pheochromocytoma and paraganglioma in adults and a similar drug to treat neuroblastoma in children.
What are the benefits of theranostic medicine?
Therapeutic treatments generally do not cure cancer, but they do prolong the length and quality of life of patients. Theranostic treatment is well tolerated, so the risks of side effects to patients are usually outweighed by the benefits, including a reduction in symptoms caused by the cancer.
What are the side effects of theranostic medicine?
Because the body is exposed to radiation - even though this radiation is highly targeted - it can slightly increase the chance of developing other cancers. One common adverse reaction is that levels of certain blood cells may decrease somewhat because the treatment can "stun" the bone marrow, where blood cells are produced. This is usually temporary. Some patients experience fatigue and gastrointestinal symptoms such as nausea and loss of appetite.
Other side effects are more specific to the therapy. For example, in prostate cancer therapy with PSMA, patients may experience dry mouth because their salivary glands receive some radiation. All of these potential side effects are carefully monitored. Blood counts are checked after each infusion to make sure the blood cells tolerate the treatment.
What happens during a theranostic procedure?
Patients first receive an intravenous injection containing the radioactive tracer. It takes approximately one hour for the radioactive tracer to absorb and bind to the cancer cells; then the body scan is performed.
The results of the scan (diagnosis) will show if there is cancer and where it is located in the body. A nuclear medicine doctor will review these images and send a report to the oncologist. This information will help the doctor decide whether to go ahead with further radioactive tracer treatment. The infusionmis done in an infusion therapy unit where there are special treatment rooms and bathrooms designed for theranostic treatments. It usually takes only a few minutes, followed by a period of observation. After a few days, the radiation is eliminated from the body through body fluids.
