Papillary thyroid microcarcinoma with minimal extrathyroidal extension. Is its course so indolent that it requires a less aggressive treatment?

Although the incidence of papillary thyroid microcarcinoma (PTMC) has increased in recent decades, the role played by minimal extrathyroidal extension (mETE) in the prognosis of PTMC is still unclear. The aim of this study is to analyze the factors associated with PTMC with mETE and its long-term prognosis. We conducted a retrospective study on patients with a histological diagnosis of PTMC. We excluded patients who had previously undergone thyroid surgery, those who had other synchronous malignancies, those with an ectopic location of the PTMC, and those lost to follow-up within 2years. We compared group 1 (PTMC without extrathyroidal extension) to group 2 (PTMC with mETE) and performed a multivariate analysis. We observed PTMC with mETE in 11.2% (n=18) of patients. On the multivariate analysis, mETE was associated with age ≥45 years (OR: 4.383; 95% CI: 1.051-18.283, p = .043), tumor size ≥8mm (OR: 5.913; 95% CL: 1.795-19.481; p = .003), bilaterality (OR: 4.430; 95% CI: 1.294-15.173; p = .018) and metastatic lymph nodes (OR: 12.588; 95% CI: 2.919-54.280; p = .001). During a mean follow-up of 119.8±65 months, one recurrence was detected in group 2 (0% vs. 5.6%; p = .112). No patients died of the disease. Disease-free survival was lower in group 2 (124.9±5.6 vs. 97.4±10.3 months; p = .034). The mETE of PTMC is a factor of worse prognosis associated with the presence of metastatic lymph nodes and a lower rate of disease-free survival.