Age, not tumor size, modifies the association between extrathyroidal extension and long-term outcomes in patients with follicular cell-derived thyroid carcinoma

BACKGROUND:
Follicular cell-derived thyroid carcinomas (FCTC) are common, with stable mortality rates but significant recurrence risks. Extrathyroidal extension (ETE) affects recurrence risk and staging. The 8th edition of the AJCC/TNM classification excludes microscopic ETE from upstaging but considers gross ETE a significant factor in older patients.


OBJECTIVE:
This study examines clinical outcomes and disease-free survival (DFS) in FCTC patients with and without ETE, evaluating the modifying effects of age and tumor size on incomplete response risk.


DESIGN:
A single-center retrospective chart review was conducted at King Abdulaziz University Hospital, Jeddah, Saudi Arabia


SETTING:
King Abdulaziz University Hospital


PATIENTS AND METHODS:
Patients aged ≥13 years diagnosed from January 2017 to December 2021 with long-term follow-up (≥18 months) were included. Medullary and anaplastic thyroid cancers were excluded. Data on demographics, tumor characteristics, risk stratification, and clinical outcomes were collected. Response to therapy was categorized per the 2015 ATA guidelines. Chi-square and Multivariable analysis assessed interactions between age, tumor size, and ETE in predicting incomplete response. Kaplan-Meier curves visualized survival differences.


MAIN OUTCOME MEASURES:
Identifying the interactions between age and tumor size with ETE to predict the risk of incomplete response to therapy among patients with FCTC.


SAMPLE SIZE:
255 patients. The median follow-up duration was 4 years.


RESULTS:

Patients with ETE were present in (n=38) 15.7% (8% microscopic, 7% gross). Older patients (≥55 years) with ETE had 26.47-fold higher odds of incomplete response than younger patients. Tumor size independently predicted incomplete response, but its interaction with ETE was not significant. Patients with ETE had a significantly higher incomplete response rate (58% vs. 17%,
P
=.0001).



CONCLUSION:
Older patients with ETE face a markedly higher risk of incomplete response. Tumor size is an independent risk factor in those patients. Management should be stratified by age, advocating more aggressive management for older patients with ETE.


LIMITATIONS:
Retrospective, and single-center design.