CLINICAL AND PARACLINICAL CHARACTERISTICS AND EFFICACY OF 30MCI I-131 RAI AFTER SURGERY OF PAPILLARY THYROID CANCER ASSOCIATED WITH HASHIMOTO’S THYROIDITIS

Abstract

Objectives: Papillary thyroid carcinoma patients associated with Hashimoto's thyroiditis (PTC with HT) commonly present in clinical practice. The objective of the study was to investigate the clinical characteristics and effectiveness after one course of thyroid remnant ablation with 30 mCi of I-131 in this patient group according to the guidelines of the ATA 2015.

Methods: From January 2019 to June 2020, we conducted a retrospective study on 234 low-to moderate-risk PTC patients. All of these patients underwent total thyroidectomy and cervical lymph node resection (if lymph node metastasis was suspected). The exclusion criteria were concomitant presence of other cancer, suspected cervical lymph node metastasis on post-surgery ultrasound, detection of metastasis findings on post-therapy WBS. Therapy response was evaluated 3-6 months after an ablation dose of 30 mCi I-131. The response criteria were standardized according to those of the ATA guideline.

Results: 234 patients were included in the study, 194 (83%) were classified as intermediate risk and 40 (17.1%) as low risk. 207 (88.5%) were in stage 1, and 27 (11.5%) were in stage 2. There are 47 patients (20.1%) had concurrent Hashimoto's thyroiditis. The patient group with Hashimoto's thyroiditis (PTC with HT) had the following characteristics compared to the PTC group: a higher proportion of females (95.7% vs. 78.1%, p=0.003), a higher proportion of thyroglobulin levels <2 ng/ml, and a lower proportion of thyroglobulin levels between 2 ng/ml and 10 ng/ml (74.5% vs. 19.1%; 33.7% vs. 41.2%, p<0.001). The positive rate of thyroglobulin antibodies was also higher in the PTC with HT group compared to the PTC group (53.2% vs. 8.6%, p<0.001). Other factors such as age, tumor size, tumor stage, extrathyroidal invasion, lymph node metastasis, disease stage, and risk stratification showed no statistically significant differences between the two groups.After one course of I-131 treatment, there were no statistically significant differences in the complete response rate, incomplete structural response rate, incomplete biochemical response rate, and indeterminate response rate between the two groups with and without thyroiditis (56.4%, 25.6%, 2.6%, and 15.4%; 51.7%, 19.3%, 4%, and 25%, p=0.566).

Conclusion: Papillary thyroid cancer patients associated with Hashimoto's thyroiditis have a female predominance, higher levels of sTg (<2ng/ml), and higher levels of positive TgAb, all of which have statistical significance when compared to the PTC group. There is no difference in treatment response after one low-dose I-131 treatment between PTC with and without Hashimoto's thyroiditis.

Key words: PTC, Hashimoto’s thyroiditis, radioiodine ablation