Differentiated thyroid cancer cells express TSH receptors on their surface, and TSH stimulation increases the expression of Tg and NIS and accelerates tumor growth. The use of higher than physiological dose of thyroid hormone preparation – levothyroxine sodium (Euthyroxine) can inhibit TSH secretion, suppress thyroid cancer cell growth and reduce the risk of recurrence.
I. Indications of thyrotropin suppression therapy for differentiated thyroid cancer
The best indication for suppressive therapy is differentiated thyroid cancer aged <65 years without cardiovascular disease, especially for high-risk group and premenopausal women.
2. Suppressive therapy is also indicated after total thyroidectomy for differentiated thyroid cancer, especially within 5 years after surgery when the cancer is prone to recurrence.
3. Suppressive therapy should be given when there are some poor prognostic factors, such as thyroid cancer without iodine uptake, age >40 years, mass diameter >4 cm, invasion of the envelope, etc.
Choice of agent
It has a long half-life of about 7 days and has a precise thyroxine content without allergic reactions.
Third, the mastery of the dose
The dose of levothyroxine should be decided according to the concentration of TSH in the serum, requiring TSH to fall to a certain value, while T3, T4, FT3 and FT4 are maintained within the normal range. The target TSH values are recommended for patients with intermediate to high risk thyroid cancer, who should be treated with total suppression of TSH <0.1 mU/L. Low risk patients should be treated with partial suppression of TSH to 0.1-0.5 mU/L.
Levothyroxine is started at a small dose of 25 – 50 μg/d and increased by 25 μg every 1-2 weeks to the therapeutic target TSH value.
Note that the dose of thyroxine must be reduced with increasing age to avoid osteoporosis and increased myocardial oxygen consumption. The dose must be increased in the presence of the following factors.
1, people with gastrointestinal malabsorption: such as hepatic sclerosis, short bowel syndrome, etc.
2, while taking certain drugs that prevent T4 absorption: such as aluminum hydroxide, aluminum thiosulfate, ferrous sulfate, lovastatin (cholesterol-lowering drugs), anti-cholestatic ammonia, etc.
3, pregnancy, etc.
IV. Duration of administration
It is recommended to take it for a lifetime. In the low-risk group, total suppressive therapy can be administered within 5 years after surgery and closely followed up; after 5 years, if there is no recurrence, partial suppressive therapy or no treatment can be given. In case of metastasis or recurrence, surgical resection or other non-surgical treatment will be performed.
If the initial surgery is total thyroidectomy or postoperative iodine ablation therapy, monitor the serum thyroglobulin (TG) level during follow-up; if the serum TG increases >5ng/ during suppressive therapy, we must be alert to tumor recurrence or metastasis.
V. Adverse effects of suppressive therapy
As long as the dosage of thyroxine is appropriate, most of the adverse reactions are not significant.
Once the dose is too high, the following three hazards can be caused and must be prevented.
1, hyperthyroidism (hyperthyroidism) or subclinical hyperthyroidism: can be avoided by regular review of thyroid function, so that T3, T4, FT3 and FT4 in particular are maintained within the normal range.
2. Osteoporosis: It is characterized by bone pain, increased blood calcium, urinary calcium and osteoporosis, and decreased serum parathyroid hormone, especially in those with insufficient calcium intake, alcohol consumption, tobacco addiction, hormone dependence and menopausal women.
3, increased myocardial oxygen consumption, promoting angina pectoris, and even myocardial infarction. Therefore, inhibitory therapy must be used with caution or abandoned in patients with coronary arteriosclerotic heart disease, hypertensive heart disease or elderly patients, as well as in patients with atrial fibrillation.