A quantitative assessment of the number of disease foci in papillary thyroid cancer.

[AIM] Multifocality is a frequent feature of papillary thyroid carcinoma (PTC). Its prognostic value is controversial although national guidelines recommend treatment intensification if present. However, multifocality is not a binary but discrete variable. This study aimed to examine the association between increasing number of foci and risk of recurrence following treatment.

[METHODS] 577 patients with PTC were identified with median follow-up of 61 months. Number of foci were taken from pathology reports. Log-rank test was used to assess significance. Multivariate analysis was performed and Hazard Ratios were calculated.

[RESULTS] Of 577 patients, 206(35%) had multifocal disease and 36(6%) recurred. 133(23%), 89(15%) and 61(11%) had 3+, 4+ or 5+ foci respectively. The 5-year RFS stratified by number of foci was 95%v93% for 2+foci (p = 0.616), 95%v96% for 3+foci (p = 0.198) and 89%v96% for 4+foci (p = 0.022). The presence of 4 foci was associated with an over 2-fold risk of recurrence (HR 2.296, 95% CI 1.106-4.765, p = 0.026) although this was not independent of TNM staging. Of the 206 multifocal patients, 31(5%) had 4+foci as their sole risk factor for treatment intensification.

[CONCLUSION] Although multifocality per se does not confer worse outcome in PTC, finding 4+foci is associated with worse outcome and could therefore be appropriate as a cut-off for treatment intensification. In our cohort, 5% of patients had 4+foci as a sole indication for treatment intensification, suggesting that such a cut off could impact clinical management.