Validation of the Updated Porto Proposal in Papillary Thyroid Microtumors: Analysis of Cases at a University Hospital in Catalonia, Spain

<b>Background/Objectives</b>: Given the high incidence and generally favorable prognosis of papillary thyroid microcarcinomas (PTMs), the Porto Proposal aims to refine the management of these tumors. It designates tumors lacking certain risk factors as papillary microtumors (PMTs) to avoid overtreatment and reduce patient stress. The updated Porto Proposal (uPp) suggests criteria for reclassifying incidental PTMs as PMTs. This study seeks to validate these criteria using data from a university hospital in Catalonia, Spain, and assess the clinical and pathological characteristics of PTMs. <b>Methods</b>: This retrospective study analyzed patients diagnosed with PTM (≤1 cm) at a university hospital from 2000 to 2024. The study examined variables, including lymph node positivity, incidental diagnosis, tumor location, histological type, treatment, multifocality, age at diagnosis, tumor size, and survival. The uPp criteria were applied to reclassify PTMs into PMTs or PMCs (true papillary microcarcinomas). Student's <i>t</i>-test and chi-square tests were used to evaluate the associations between these variables and the uPp classification. <b>Results</b>: The cohort comprised 107 patients, with 77 (72%) women and 30 men. The mean age at diagnosis was 54.5 years. Out of the total, 77 (72%) cases were reclassified as PMTs and 30 (28%) as PMCs according to the uPp criteria. PMC tumors were larger (mean size 4.5 mm vs. 3.3 mm for PMT, <i>p</i> = 0.014) and were significantly associated with multifocality (52.2%; <i>p</i> = 0.004). Most lymph node-positive cases were classified as PMCs (69.2%; <i>p</i> < 0.001) and were multifocal and bilateral more commonly. However, no significant differences in outcomes between PMCs and PMTs were found (<i>p</i> = 0.188). Follicular histology was significantly more common in PMTs (87.0%, <i>p</i> < 0.001) and rarely had lymph node metastases (4.6%; <i>p</i> = 0.047). <b>Conclusions</b>: The updated Porto Proposal (uPp) effectively identifies PTMs with minimal malignant potential, distinguishing between PMT and PMC. The findings support the protocol's use in reducing unnecessary treatments and psychological stress for patients. The study highlights significant clinical and pathological differences between PTM subtypes, reinforcing the protocol's applicability in daily pathological practice.