Clinicopathologic Characteristics of Thyroid Microcarcinoma: Findings from a Hospital-Based Study in Vietnam

Background: Thyroid microcarcinoma (TMC) incidence has significantly increased in recent decades. The rates of lymph node metastasis extrathyroidal extension have been significantly different in patients with TMC ≤5 mm versus those with size >5 mm. The current analysis aimed to examine the clinicopathologic features of TMC measuring <5 mm and to compare them with those of TMC ≥5 mm. Methods: A total of 273 patients with TMC confirmed by histological examination from December 2020 to May 2021 were enrolled in Bach Mai Hospital, Hanoi, Vietnam. Unconditional logistic regression models were used to determine the association between clinicopathological factors and tumor size, central lymph node metastasis and extrathyroidal extension. Results: We found 212/273 patients (77.7%) were diagnosed incidentally. The majority of patients were female (87.5%) and had a mean age of 44.2 years. The mean tumor size (±standard deviation (SD)) was 5.72 ± 2.33 mm. Most of the patients were also diagnosed with papillary TMC. Multifocal and bilateral lesions accounted for 13.2% and 12.1%, respectively. The extrathyroidal invasion was observed in 14.7% (40 patients), while 24.5% (67 patients) were those with central lymph node metastases. The rate of extrathyroidal extension in patients with tumor size ≥5 mm was significantly higher than in patients with tumor size <5 mm (odds ratio (OR) = 4.98; 95% confidence interval (CI): 1.48–16.70; p = 0.004). Patients with body mass index (BMI) <23 kg/m² were found to be protected against the odds of extrathyroidal extension (OR = 0.38, 95% CI: 0.19–0.75; p = 0.004) compared to those with BMI ≥23 kg/m². In univariable mode, central lymph node metastasis was positively associated with the odds of the presence of extrathyroidal extension (OR = 2.70, 95% CI: 1.34–5.45; p = 0.004). In the multivariable model, central lymph node metastasis was also associated with the presence of extrathyroidal extension (OR = 2.507, 95% CI: 1.194–5.264; p = 0.017). Univariate analysis demonstrated that tumor size ≥5 mm (OR = 2.04; 95% CI: 1.01–4.17; p = 0.047) and extrathyroidal extension (OR = 2.71; 95% CI: 1.34–5.45; p = 0.004) were risk factors of central cervical lymph node metastasis. In multivariable models, the extrathyroidal extension was associated with central lymph metastasis. Conclusions: TMC <5 mm tumor size is less likely to have aggressive characteristics, including extrathyroidal extension, than a TMC ≥5 mm. Long-term follow-up studies are thus warranted to investigate the factors in the prognosis of TMC.