The Role of Risk Factors for the Progression of Patients with T1b-T2 Papillary Thyroid Carcinoma (PC) during Long-Term Follow-Up

Background/Objectives: Recurrence prediction for patients with PC and tumor sizes ranging between 1 and 4 cm, classified as T1b and T2, remains a controversial problem. We evaluated which risk factors, identified during the primary tumor surgery, might play a prognostic role in predicting disease progression. Methods: We retrospectively enrolled 363 patients with classic PC who were in follow-up (207 T1b, 156 T2), with tissue risk factors at surgery in 209/363 cases. In all cases, an 131I-whole-body scan, SPECT/CT, and US were employed to detect any metastases during follow-up, and histology was used to confirm lesions. In the absence of surgery, metastases were validated by radioisotopic and radiologic procedures, eventually culminating in a needle biopsy and sequential thyroglobulin changes. Results: Metastases occurred in 61/363 (16.8%) patients (24 T1b, 37 T2). In 50/61 cases, the following risk factors were identified: minimal extrathyroid tumor extension (mETE) alone in 12/50 patients, neck lymph node (LN) metastases in 8/50 cases, and multifocality/multicentricity (M/M) in 6/50 cases. In the remaining 24/50 cases, the risk factors were associated with each other. From a Cox regression multivariate analysis, metastasis development was significantly (p < 0.001) influenced by only mETE and LN metastases, with a shorter disease-free survival (log-rank test). Conclusions: The current study proves that mETE and neck LN metastases are associated with aggressive PC. While LN metastasis’ role is known, mETE’s role is still being debated, and was removed by the AJCC’s eighth edition because it was considered to not be associated with an unfavorable prognosis. However, this interpretation is not supported by the present study and, according to comparable studies, we suggest a revision of the mETE classification be considered in the next AJCC edition.