Endocrine Abstracts

Introduction: The recurrence rate of intermediate-risk differentiated thyroid carcinoma (DTC) ranges between 5% and 20% and the therapeutic strategy requires further evaluations.

Aim: We therefore investigated the potential risk factors for post-treatment recurrence of intermediate-risk DTC at 1 and 3 years from diagnosis.

Methods: This retrospective observational study included 121 patients who underwent thyroidectomy for intermediate-risk DTC between January 2017 and December 2020 in two Italian centres (Endocrinology, Diabetology and Metabolism - Department of Medical Sciences, Turin and Endocrinology - Department of Translational Medicine, Novara). For each patient, demographic, biochemical and histopathological features of DTC were evaluated. Moreover, data about radioiodine (RAI) treatment were recorded and rate of tumour recurrence at 1 and 3 years from diagnosis was assessed. Multivariate logistic regression models were used to identify risk factors for tumour recurrence.

Results: Most of patients were females (M/F:1/3) with an age at diagnosis >55 years in 69.4% of cases. Overall, 92 patients (76.0%) underwent RAI treatment. This subgroup had a higher prevalence of microscopic extrathyroidal extension (mETE) of the tumour (53.3% vs 31.0%, P=0.03) and clinical lymph node metastasis at diagnosis (74.4% vs 45.0%, P=0.01), as well as higher number (5.5 ± 4.5 vs 1.8 ± 0.7, P=0.02) and dimensions (12.2 ± 8.4 vs 0.6 ± 0.7, P=0.01) of metastatic lymph nodes than patients who did not undergo RAI. Tumour relapse was observed in 18.1% and 20.7% of cases at 1 and 3 years from diagnosis, respectively, without significant differences between subgroups. Multivariate logistic regression analysis did not show any significant association between the presence of tumour relapse and DTC histopathological phenotype. The presence of clinical lymph node metastasis and radioiodine dose, a higher stimulated Tg levels in patients undergoing RAI (OR=1.02, 95%CI 1.00-1.03, P=0.04) and a lower age at diagnosis (OR=0.93, 95%CI 0.87-0.99, P=0.03) emerged as the only independent risk factors for 1 year-tumour relapse. Instead, the 3-year-tumour relapse was independently predicted only by the presence of 1 year-tumour relapse (OR=15.41, 95%CI 1.12-212.10, P=0.04).

Discussion: In our study, mETE and clinical lymph node metastasis represent the main indicators for referring patients to RAI. Stimulated thyroglobulin levels in patients undergoing RAI, and the age at diagnosis are the only factors that independently influence the risk of recurrences in patients with intermediate-risk DTC.