The standard treatment for differentiated thyroid cancer is primarily surgical, with postoperative follow-up determined by tumor stage and risk of recurrence, and consists of three main components:
- Surgical resection of the primary site and potentially resectable metastatic lesions.
- A subset of patients require radioactive iodine (RAI) therapy to destroy postoperative residual thyroid tissue and occult or inoperable metastatic lesions.
- Thyroxine pills are taken for life to replenish thyroxine and inhibit tumor recurrence and growth.
As you can see, RAI therapy is an important part of the equation.
What is radioactive iodine therapy?
Iodine -131 (I-131) is an isotope of the element iodine that is radioactive.
Thyroid tissue has the ability to take up iodine. When I-131 is taken, it is absorbed by the gastrointestinal tract, travels with the bloodstream, and is taken up by postoperative residual thyroid tissue and possible metastases. i-131 releases rays that can then destroy these tissues for therapeutic purposes.
Because I-131 accumulates only in the thyroid tissue, the unabsorbed portion is quickly excreted in the urine and stool, thus not damaging other organs.
Which patients need RAI?
Not all patients need an RAI, but only if all three of the following conditions are met.
- Differentiated thyroid cancer
- With total or near-total thyroidectomy
- Postoperative pathology suggesting a high risk of recurrence
It is important to note that RAI is not used alone for thyroid cancer treatment, but only as a postoperative adjuvant.
Which patients should not have RAI
?
Patients who are allergic to iodine should not be treated with RAI.
Pregnant and breastfeeding women should not receive RAI therapy. If you are pregnant at the time of thyroid cancer diagnosis, your doctor will give special instructions. Most pregnant women can wait until after delivery to have surgery. If surgery is needed sooner, it is best to schedule it in the middle of pregnancy (around 22 weeks).
There is no professional consensus on the age limit for I-131 treatment. The elderly and adolescents under 18 years of age are not currently considered contraindicated for RAI treatment.
What factors affect the efficacy of RAI?
Iodine uptake is a major factor in RAI.
Iodine uptake depends primarily on a “carrier” protein in the thyroid follicle called the sodium-iodine isotransporter (NIS), and mutations in the NIS gene can affect the localization and expression of the NIS and thus the efficacy of RAI therapy.
If the NIS gene is mutated, it affects the localization and expression of the NIS, thus affecting the effectiveness of RAI therapy.
It is generally accepted that a clean and complete total thyroidectomy and adequate RAI prep are necessary to improve outcomes.
Related reading:
Is RAI treatment safe?
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Co-written by Dr. Kai Guo, Fudan University Cancer Hospital