Extrathyroidal extension of primary lesion influences thyroid cancer outcomes

Abstract

Abstract Aims: Extrathyroidal extension (ETE) is a determined factor of T3 and T4 stage of differentiated thyroid cancer (DTC) in American Joint Committee on Cancer (AJCC). We aimed to compare clinical outcomes between different extent of ETE according to tumor size.Methods: Patients diagnosed with DTC were collected from the Surveillance, Epidemiology, and End Results (SEER) database from 2004 to 2015. They were categorized into two groups by presence of lymph node metastases (LNM) or distant metastases (DM): group A: no presence of LNM and DM, group B: presence of LNM or DM. Each group was further divided into four groups according to tumor size: £1cm, 1-2cm, 2-4cm, >4cm. ETE was divided into three groups by the extent: no ETE, microscopic ETE, and macroscopic ETE. Kaplan–Meier method and log-rank test were used to analyze cancer-specific survival (CSS).Results: 91975 patients were included. In group A and B, for tumor size £1cm, there was no significant difference in CSS between no ETE and microscopic ETE, while significant difference was observed between no ETE and macroscopic ETE. For tumor size >1cm, there were significant differences in CSS (both no ETE vs micro ETE and no ETE vs macro ETE).Conclusions: We suggests that when tumor size is more than 1cm, micro ETE is significantly associated with poorer outcome. T3 and T4 stage may take account into tumor size rather than merely based on the presence and extent of ETE. It may be prudent to revisit the omission of micro ETE in TNM staging