Metaiodobenzylguanidine (MIBG) is a compound and structural analogue of the norepinephrine neurotransmitterbased on its chemistry. It owns a peculiar feature to selectively accumulate in the certain structures of central nervous system. The compound is used as a radiopharmaceutical agent (radiotracer) for diagnostics and treatment of different oncologic pathologies.
Core of the treatment technique
Metaiodobenzylguanidine contains radioactive iodine (a radiopharmaceutical agent labeled with iodine atoms - I131) as a part of molecule. That’s why it emits a small amount of radiation. Since this radiotracer is a structural analogue of norepinephrine, it is selectively accumulates in the central nervous structures and in the adrenal glands after the parenteral (avoiding digestive tract) administration. Cells die due to the radiation in the region of MIBG accumulation. This feature is used to destroy tumors that predominantly have a neurodermal origin (neuroendocrine tissues that have adrenergic innervation).
Key factor for MIBG use is a presence of inoperable tumor pathology, which develops from neuroendocrine tissue.Such oncologic processes include pheochromocytoma, paraganglioma, carcinoid tumors, neuroblastoma, metastatic and recurrent medullary thyroid cancer.
This is a tumor of adrenal medulla that produces catecholamine hormones (epinephrine, norepinephrine) during its growth. Tumor is peculiar with the absence of malignancy and metastases. However, it leads to considerable functional changes of cardiovascular and nervous system because of the increased catecholamine level in the blood. MIBG accumulates in the tumor in 88% of cases which partially destroys cancerous cells and reduces the size of malformation. Also, this helps to decrease level of catecholamine hormones in the blood. 60% of patients are noticed to have stabilized course of the oncologic process.
Paraganglioma is a benign brain malformation peculiar with the slow growth and paraganglionic cells origin. Malformation is not life-threatening itself, though its placement in the human brain may lead to disruption of its various structures and to violation of its function. MIBG accumulates very well in paraganglioma and helps to significantly reduce the size of malformation after a therapy series (46% of cases).
Carcinoid tumors represent malformations located in digestive tract and pancreas. Tumors have enterochromaffin origin and are characterized by malignant growth and metastases. Radiopharmaceutical agent accumulates well in the cells of malformation after MIBG administration in 69% of cases. MIBG accumulation leads to the cells death, reduction of the tumor and its metastases. Meanwhile, tumor reduces twice after a therapy course in 63% of cases.
Neuroblastoma is an embryonic tumor localized in the structures of the sympathetic part of the nervous system. MIBG accumulates well in the tumor in 90% of cases. Correct dosage leads to regression (reverse development) of the malformation in 36% of cases.
Medullary thyroid cancer
Medullary thyroid cancer is a comparatively rare malignant formation with the aggressive growth and hormones production (a hormone-active tumor).
Recurring course of medullary thyroid cancer with the formation of metastases (daughter formations) in other areas of the body, the only alternative treatment is the use of MIBG.
Fine radiopharmaceutical agent accumulation is registered in the majority of cases. This technique allows partial regression of medullary thyroid cancer and its metastases in 40% of cases. Patients’ condition stabilizes in 60% of cases.
Absolute medical contraindication for the use of MIBG with a therapeutic purpose is the individual intolerance to the radiopharmaceutical agent, as well as the development of a pronounced allergic reaction.
Relative medical contraindications include:
- Unacceptable risk of patient’s isolation
- Progressive decrease in the kidneys function
- Myelosuppression which is a decrease in the number of certain leukocytes in the blood (neutrophils, basophils, eosinophils)
- Expressed changes in the state of peripheral blood
In case a patient has some relative contraindications, they first perform therapy to improve kidneys or blood condition and then only start MIBG.
Side effects are possible during the therapy course which include nausea, vomiting form time to time, worsening of the bone marrow function.
MIBG doses, the regimen of application and the duration of the therapy course are chosen individually for each patient. A control study with a visualization of the malformation, determination of its size, and also the level of catecholamine hormones in the blood should be prescribed during the therapy. Condition of a bone marrow, kidneys and also of the peripheral blood is supervised repeatedly.
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Author: Dr. Nadezhda Ivanisova