Endocrine Abstracts

Introduction: PTC patients with lymph node (LN) metastases of greater volume (in>5 LN and/or with larger metastases >5mm, hereinafter N1>5) usually receive radioiodine (RAI). Some guidelines suggest carrying out an evaluation of the response to surgical treatment (RST), recommending lower RAI dose (activity) in patients with good RST.

Objectives: a)To evaluate the RST in patients with PTC and N1>5 b)To evaluate the disease-free-survival (DFS) in patients with PTC and N1>5 who present thyroglobulin (Tg) <1.0 ng/ml, absence of Tg-Antibodies (TgAb (-)) and non-suspicious ultrasound (US) findings in the evaluation of the RST and who are treated with low doses of RAI.

Experimental Design: Prospective Observational Cohort Study

Materials and Methods: Patients with PTC and N1>5, operated between 2016 and 2020 and who had RST evaluation by US, Tg and TgAb (using LT4) and with TSH≤2.0mIU/ml at least 6 weeks after surgery and prior to the administration of RAI were included. Patients were divided into 3 groups according to the RST (Table 2). Low-dose RAI (30-50mCi) was offered to patients who presented RST defined in this study as adequate (Tg ≤1ng/ml, TgAb (-) and non-suspicious US, Group I). In patients with metastases ≥10mm and/or ≥10 involved LN, low-dose RAI was offered when their Tg was ≤0.2ng/ml, AcTg (-) and normal US. Continuous variables are described as median and range, and categorical variables as proportions. Study was approved by local ethics committee.

Results: Of 581 patients with LN metastases, 97 met the inclusion criteria.

In 53.7% of the patients of group I low dose (30-50 mCi) of RAI was given. With a median follow-up of 24months, DFS was 96% (only 1 patient presented a tiny 3 mm suspicious adenopathy).

Conclusions: a)Approximately half of PTC patients with N1>5 have an adequate RST. b)This preliminary data suggests that in this group of patients, the administration of a low dose of RAI would be associated with a very good disease-free survival, appearing to be a safe option in them.