TOPLINE:

The sum of diameters of all tumour foci, reflecting the intrathyroidal tumour burden, was an independent and more informative prognostic marker of treatment response than the mere presence or number of foci in patients with low- or intermediate-risk multifocal papillary thyroid carcinoma (mPTC) treated with total thyroid ablation.

METHODOLOGY:

• Researchers conducted a retrospective cohort study to assess the prognostic value of different multifocality metrics in predicting treatment response in patients with mPTC who underwent total thyroid ablation.
• They included 115 patients with low-risk (n = 91; 67 women and 24 men) or intermediate-risk (n = 24; 16 women and 8 men) mPTC from two Italian centres who underwent total or near-total thyroidectomy with or without neck dissection, followed by radioiodine therapy, between 2022 and 2024.
• Multifocality metrics were defined as the number of tumour foci, the largest foci diameter, and the arithmetic sum of the largest diameters of all tumour foci.
• Response to treatment was assessed at 6-12 months post-radioiodine therapy and classified according to the 2015 American Thyroid Association response categories: excellent response and non-excellent response (indeterminate, biochemically incomplete, and structural incomplete response).

TAKEAWAY:

• Overall, 75.6% of patients achieved an excellent response to treatment and 24.4% showed a non‑excellent response.
• Patients who achieved a non-excellent response had a larger sum of the largest diameters of all tumour foci (P < .0001), higher levels of pre-ablation basal thyroglobulin (P < .0001), and more frequent lymph node metastases (P = .006) than those who achieved an excellent response.
• Multivariable analysis revealed the sum of the largest diameters of all tumour foci ≥ 21.5 mm (odds ratio [OR], 23.2; P < .001), higher levels of basal thyroglobulin (OR, 9.85; P = .015), and lymph node metastases (OR, 6.27; P = .027) as independent predictors of non-excellent response after initial therapy.

IN PRACTICE:

"Our findings pertain to risk stratification within mPTC rather than to the prognostic role of multifocality compared with unifocal disease," the authors wrote.

"sumD [the arithmetic sum of the largest diameters of all tumour foci] may complement dynamic risk stratification as a practical, pathology-based, index of residual risk," they added.

SOURCE:

This study was led by Alfredo Campennì, Department of Biomedical and Dental Sciences and Morpho-Functional Imaging, University of Messina, Messina, Italy. It was published online on January 22, 2026, in Endocrine.

LIMITATIONS:

The retrospective design and treatment homogeneity may have introduced selection bias. The large OR for the sum of the largest diameters of all tumour foci, along with a wide CI, indicated that the model may not be stable and lacked precision. Almost half of the non-excellent responses were indeterminate. 

DISCLOSURES:

This study did not receive any specific funding. The authors declared having no competing interests.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.