Prognostic significance of the sum of the diameters of single foci in multifocal papillary thyroid cancer: the concept of new-old tumor burden.

Aim: The prognostic value of multifocality (Mu) in papillary thyroid cancer (PTC) remains controversial. The present study aimed to investigate this issue and test the possible prognostic significance of the sum of the diameters of single foci (SDSF), the total number of foci (TNF), and primary tumor size (PTS) in multifocal PTC.

Methods: We retrospectively analyzed a single-center consecutive series of 370 PTCs.