The influence of extrathyroidal extension in development of metastasis in papillary thyroid cancer

Background: Papillary thyroid cancer (PTC) course and outcome very much depend on prognosis factors. One of the most significant factors is extrathyroidal extension (ETE), which can be local or extensive. In the view of some authors, tumor grow beyond the thyroid capsule is associated with high risk locoregional and distant metastasis, which increase disease recurrence and reduce survival. Some others do not see influence of minimal ETE on disease prognosis, so we need more trials to clarify the role of ETE in PTC.

Aims: To evaluate the ETE role in development of metastasis in PTC patients.

Materials and methods: The study includes 233 patients with PTC who receive treatment in RSCRR. 185 patients had clinical N0 stage, 48 patients were with verified N1a–1b. All patients with cN0 underwent thyroidectomy with central neck dissection, patients with N1 – thyroidectomy combined with different neck dissections, also superior mediastinal lymphadenectomy if required. Within combination treatment the radioiodine therapy was carried out. The histology evaluated thyroid capsule involvement and lymph node metastasis. Data processing was carried out in a Microsoft Access database, a one-factor dispersion analysis was used for the analysis of the quantitative signs, and a χ-square criterion was used for qualitative ones. Multifactor analysis was done in SPSS20 program.

Results: Thyroid capsule extension was detected in 111 cases (47.6%), from which 92 were microscopic. 122 patients did not have ETE. The frequency of lymph node metastasis with or without ETE was 62.2% and 35.8% respectively, which is significantly more often (р = 0.000, χ2 = 21.342). In microscopic and macroscopic extension regional metastasis were 56.5% and 94.7%, distant metastasis – 1.1 and 21% respectively. Statistically significant, the ETE was more prevalent in non-encapsulated tumor cases (р = 0.000, χ2 = 15.122), and if the tumor size was more than 1cm (р = 0.026, χ2 = 7.293). Only 41% of patients with cN0 had ETE, and patients with N1 – 72.9%, which is statistically significant (р = 0.000, χ2 = 14.235).

Conclusion: ETE is a predictor of PTC metastasis. The presence of ETE requires the necessity to apply the more aggressive treatment of PTC including thyroidectomy with central neck dissection and radioiodine therapy. Gross ETE significantly increases the risk of regional together with distant metastasis.

papillary thyroid cancer, extrathyroidal extension, central neck dissection, hidden metastasis

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