Oral Abstract Presentation

CSEMO2 - CSEM: Endocrinology & Metabolism Oral Abstracts: Radioactive Iodine Activity and Predictors of Recurrence or Persistence in Intermediate-Risk Papillary Thyroid Cancer: A Retrospective Cohort Study

Friday, November 28, 2025

14:53 - 15:00 Toronto

Location: Room 201 A/B/C/D/E/F

Submitting Author(s)

Mohammad Jay, MD

Endocrinology PGY-5 Resident and PhD candidate
University of Toronto
Toronto, Ontario, Canada

Disclosure(s): I do not have a relationship with a for-profit and/or a not-for-profit organization to disclose

Presenting Author(s)

Mohammad Jay, MD

Endocrinology PGY-5 Resident and PhD candidate
University of Toronto
Toronto, Ontario, Canada

Disclosure(s): I do not have a relationship with a for-profit and/or a not-for-profit organization to disclose

First Author(s)

Mohammad Jay, MD

Endocrinology PGY-5 Resident and PhD candidate
University of Toronto
Toronto, Ontario, Canada

Disclosure(s): I do not have a relationship with a for-profit and/or a not-for-profit organization to disclose

Disclosure(s):

Mohammad Jay, MD: I do not have a relationship with a for-profit and/or a not-for-profit organization to disclose

Blinded Abstract:

Background: Papillary thyroid cancer (PTC) is the most common endocrine malignancy worldwide and the leading cancer among Canadians aged 15–29. Most intermediate-risk PTC patients receive radioactive iodine (RAI) to reduce recurrence, but evidence supporting optimal RAI dosing and clinical predictors for tailored management remain limited.

Objective: To (1) evaluate the association between RAI activity (i.e., dose) and recurrence risk and (2) identify clinical predictors of recurrence or persistent disease.

Methods: We conducted a retrospective cohort study of adults (≥18 years) with intermediate-risk PTC treated at our institution (2000–2022). RAI-treated patients were grouped by activity: low ( < 30 mCi), moderate (30–90 mCi; reference), and high (>90 mCi). To address confounding by indication, we applied inverse probability of treatment weighting; recurrence was evaluated using weighted Cox models. Predictors of recurrence or persistence were identified using multivariable logistic regression.

Results: Among 282 patients, 213 (76%) received RAI; 23 (11%) experienced recurrence. High-dose RAI was not associated with improved recurrence-free survival compared to moderate-dose (HR 1.67; 95% CI, 0.47–6.00). Kaplan–Meier analysis favored moderate-dose RAI (log-rank p=0.04). A significant treatment-by-log(time) interaction (p=0.009) indicated that excess recurrence risk with high-dose attenuated over time (C-statistic: 0.93 vs. 0.56). Overall, 100 patients (35%) had recurrence or persistent disease. Predictors included extrathyroidal extension (aOR 3.03; 95% CI, 1.56–6.25) and positive lymph node count (aOR 1.06; 95% CI, 1.02–1.12).

Conclusion: Moderate-dose RAI demonstrated comparable effectiveness and potentially lower toxicity than high-dose, supporting its novel use as a personalized treatment strategy. Extrathyroidal extension and nodal burden may inform tailored management.