Endocrine Abstracts

Objectives: Radioiodine therapy with ablative purposes is less and less used in low (LR) and intermediate (IR) risk DTC patients. The aim of this prospective ongoing study is to evaluate the clinical trend over time of patients with DTC who do not receive treatment with radioiodine.

Methods: Patients with high or intermediate-high risk in whom radioiodine treatment was performed after surgery were excluded. Data of 425 consecutive patients with DTC who joined our department for the first post-operative assessment (September 2016-December 2019), were evaluated.

Results: Most patients (70.6%) were females; the median age at diagnosis was 50 years. Total thyroidectomy was performed in 84.1% while lobectomy in 15.9%. Median tumor dimension was 1.4 cm. Histology revealed a prevalence of CV-PTC (n = 200,47.1%) and FV-PTC (n = 135,31.8%); aggressive variants of PTC were 11.8% (n = 50), while only 5.4% (n = 23) were FTC, 3.8% (n = 16) NIFT-P and 0.2% (n = 1) oncocytic tumor. In 41.9% of cases tumor was multifocal and in 12.7% mETE was detected. Lymph nodes metastases were present in 7.5% of cases. According to ATA 2015 guidelines, 316 (74.4%) patients were LR and 109 (25.6%) IR. After excluding patients treated with lobectomy and those with NIFT-P, 345/425 (81.2%) were evaluated at the first post-operative evaluation [median 4 months]. Of these, 253/345 (73.3%) showed not interfering TgAb (TgAb-neg), and median Tg value was 0.18 mg/l; conversely, 90 (26.1%) patients had interfering TgAb (TgAb-pos) with a median value of 23.5 IU/ml. Median TSH value was 0.54 mUI/l. Neck US was negative for persistent disease in all cases. Following this evaluation, 32 (9.3%) patients performed radioiodine treatment for histologic features of greater aggressiveness. After a median of 49 months, 313 patients were on follow-up without any additional treatment. Of these, 273 (87.2%) were TgAb-neg with a median Tg value of 0.15 mg/l and 40 (12.8%) were still TgAb-pos with a median TgAb value of 20 IU/ml. Median TSH value was 0.98 mUI/l. In all cases neck US persisted negative.

Conclusions: In LR and IR DTC patients, post-operative evaluation is able to discriminate patients requiring radioiodine treatment (<10%). In our series, all patients who were not immediately treated after the first post-operative evaluation did not experience disease recurrence after a median of 4 years of follow-up. Therefore, when properly selected, not only LR but also some IR DTC can successfully and safely avoid the ¹³¹I treatment.