[Results of active surveillance of clinical progression in low-risk papillary thyroid microcarcinoma: a single center prospective cohort study].

<b>Objective:</b>To observe the clinical progression of low-risk papillary thyroid microcarcinoma（LR-PTMC）, analyze the influencing factors of its oncological outcomes, and explore the feasibility of active surveillance（AS） of LR-PTMC. <b>Methods:</b>This study adopted a prospective observational research design. A total of 85 subjects diagnosed with LR-PTMC during health checkup in Health Management Center of our hospital from March 2021 to October 2022 were enrolled as the research subjects, for at least 2 years of AS follow-up observation. The clinical progress and oncological outcomes were recorded, disease progression was defined as any increase in nodule diameter ≥3 mm or the appearance of new lesions or lymph node metastasis or distant metastasis, and the oncological outcome was use disease progression defining. Cox proportional hazards regression model was used to analyze the influencing factors of oncological outcomes in LR-PTMC patients. <b>Results:</b>A total of 85 LR-PTMC patients who underwent physical examinations were included in this study. The median follow-up time was 2 years, and a total of 23 patients（27.06%） experienced disease progression. Among them, 18 patients（21.18%） had enlarged lesions（any nodule diameter increased by ≥3 mm）, and 5 patients（5.88%） had abnormal or metastatic cervical lymph nodes. The 2-year cumulative disease progression rate was 9.41%. The incidence age of LR-PTMC patients was younger, with a higher proportion of ≤45 years old. The proportion of baseline nodules with a maximum diameter greater than 5 mm is higher, and the proportion of baseline TPO Ab positivity was higher. Ultrasound showed a higher proportion of microcalcifications compared to the non progression group, and the differences were statistically significant（all <i>P</i><0.05）. Multivariate Cox proportional hazards regression analysis showed that age of onset ≤45 years <i>RR</i> 95% <i>CI</i> 1.052（1.018-1.088） and ultrasound showing microcalcifications <i>RR</i> 95% <i>CI</i> 3.361（1.379-8.194） were independent risk factors affecting disease progression during AS in LR-PTMC patients（<i>P</i><0.05）. <b>Conclusion:</b>Most LR-PTMC patients maintain stable lesion size and low lymph node metastasis rate during the AS process, with good oncological outcomes in the short term. AS can be considered as a safe and effective alternative to surgical treatment for LR-PTMC patients. But for patients with onset age ≤45 years and microcalcifications, the follow-up interval can be shortened for close observation.