Thyroid cancer does not constitute the majority (about 1.1%) of the many neoplastic diseases, but it is one of the most proportional among endocrine tumors. Differentiated thyroid cancer (papillary or follicular thyroid cancer) and its recurrent or metastatic foci can be treated with 131I. 131I treatment for differentiated thyroid cancer (DTC) has a history of 60 years internationally and has been carried out in China for nearly 50 years. The combination of surgical resection + 131I therapy + thyroid hormone suppression therapy is internationally recognized as the ideal treatment option for DTC. The first step of thyroid cancer treatment is surgical resection of primary and metastatic foci. Patients with postoperative pathological diagnosis of papillary or follicular thyroid cancer should consult the nuclear medicine department and consider post-surgical “nail clearing” treatment (i.e., elimination of residual normal thyroid gland with 131I). The second step of thyroid cancer treatment is “nail clearing” for patients with differentiated thyroid cancer who are at high risk.
Reasons for “nail clearing” treatment
(1) 131I destroys microscopic thyroid cancer lesions that are difficult to detect in the postoperative thyroid tissue.
(ii) It facilitates whole-body 131I imaging.
③ It is useful for monitoring thyroid cancer by measuring Tg level.
④ papillary carcinoma has a tendency of bilateral, microscopic multifocal, local lymph node metastasis, long local latency and development period, and high recurrence rate.
⑤ Differentiated thyroid carcinoma has local infiltrative features and an increased possibility of recurrence.
The current retrospective study found that 131I clearance of residual thyroid tissue after DTC reduced tumor recurrence and decreased morbidity and mortality; similar effects were not found in low-risk patients; however, prospective study results are lacking.
Nuclear medicine experts recommend.
(i) no thyroid hormone after thyroidectomy, and 131I directly after surgery to remove residual thyroid tissue 4-6 weeks after surgery.
(ii) Since more than half of patients with surgical residual thyroid tissue or functional metastases produce enough thyroid hormone to suppress TSH to reach 30 μIU/mL, TSH levels may not be considered during nail clearing therapy in these cases.
(iii) 131I whole-body imaging prior to nail clearing therapy is not necessary. A more common clinical method is to perform a whole-body scan 5-7 days after high-dose 131I treatment.
After nail clearing treatment, when the patient’s serum Tg ≤ 2ng/ml (in the state of not taking thyroid hormone), the treatment objective is achieved. Thyroid hormone suppression therapy was started and regular follow-up was performed at the nuclear medicine department. At the follow-up, Tg≥10ng/ml (in the state of not taking thyroid hormone or Tg>5ng/ml when taking thyroxine TSH suppression therapy) or recurrent and metastatic lesions are found, treatment of 131I recurrent and metastatic lesions should be performed.
The third step of functional thyroid cancer treatment is 131 therapy for recurrent and metastatic lesions. Since differentiated thyroid cancer cells have iodine uptake function, the lesions can gather 131I and play a therapeutic role through the radiation biological effect of β-rays. Clinical practice proves that most papillary carcinomas and follicular carcinomas are sensitive to 131I, and the clinical efficacy is certain. The treatment can be repeated every 3-4 months under normal circumstances.
What are the contraindications for treatment of differentiated thyroid cancer?
①Women during pregnancy and lactation.
②Those whose wounds have not completely healed after thyroid surgery.
③Severe impairment of liver and kidney function with WBC <3.0×109/L.
What preparations should be made to treat patients with differentiated thyroid cancer?
A: Stop taking thyroid tablets or L-T4 for 4-6 weeks (the aim is to raise TSH to about 30 μIU/mL), avoid iodine for 2-4 weeks, and measure thyroid hormones, TSH, Tg, TgAb, blood count, liver and kidney function, ECG, chest X-ray, etc. It is recommended to give a low iodine diet (dietary iodine < 50μg/d) for 1-2 weeks.