Multifocal papillary thyroid carcinoma: the impact of multifocality metrics on the response to treatment.

AIM: The prognostic significance of multifocality in papillary thyroid carcinoma (PTC) remains debated, with conflicting literature. Alternative multifocality metrics such as the number of foci and the sum of foci diameters (sumD) have been proposed as potentially more informative than the traditional largest-focus diameter (maxD). This study assessed the prognostic value of different multifocality metrics in a homogeneously treated cohort of patients with multifocal PTC (mPTC). MATERIALS AND METHODS: We retrospectively reviewed 115 low to intermediate-risk mPTC patients who underwent (near)-total thyroidectomy, with or without neck dissections, followed by radioiodine therapy. Response to initial treatment was evaluated at 6–12 months according to the 2015 American Thyroid Association risk-stratification system. Demographic, clinical, and pathological variables, including multifocality metrics, were correlated with treatment response using univariable and multivariable logistic regression analysis. RESULTS: An excellent response (ER) was observed in 87 patients (75.6%), while 28 (24.4%) had a non-excellent response (nER). Larger sumD, higher pre-ablation thyroglobulin, and lymph node metastases were significantly more frequent in the nER group. On multivariable analysis, sumD ≥ 21.5 mm, higher thyroglobulin, and lymph node metastases were independent predictors of nER. CONCLUSION: Within this exclusively mPTC cohort, sumD emerged as an independent predictor of treatment response, even in patients managed with total thyroid ablation. These findings do not address the role of multifocality per se in treatment selection but support further prospective investigation of sumD as an adjunct risk metric in postoperative risk refinement.