Elsevier

Oral Oncology

Volume 51, Issue 8, August 2015, Pages 759-763
Oral Oncology

Characteristics and significance of minimal and maximal extrathyroidal extension in papillary thyroid carcinoma

https://doi.org/10.1016/j.oraloncology.2015.05.010Get rights and content

Highlights

  • We investigated the significance of minimal versus maximal ETE in PTC.

  • ETE correlated with tumor size, lymphovascular invasion and lateral LN metastasis.

  • Minimal ETE did not correlate with recurrence and survival in PTC.

  • Maximal ETE was related to higher recurrence rate and decreased survival.

Summary

Objectives

Maximal extrathyroidal extension (ETE) is known to be an important prognostic factor in papillary thyroid carcinoma (PTC). However, the significance of minimal ETE is controversial. The aim of this study was to investigate the clinicopathologic characteristics and prognostic significance of minimal vs maximal ETE in PTC.

Materials and methods

A group of 967 patients who underwent thyroidectomy for PTC in a tertiary hospital between January 2000 and December 2011 were studied retrospectively. Patients were classified into three groups: absence of ETE, and minimal and maximal ETE. The minimal ETE group was further categorized into two subgroups according to invasion of strap muscles or no invasion (STI+ and STI−).

Results

Gender did not differ between the three groups of patients. The mean age of the patients with maximal ETE was significantly higher than in those belonging to the other groups. Tumor size, bilaterality, lymph node metastasis and stage increased significantly according to the degree of ETE. Recurrence and survival rates did not differ between the absence and minimal ETE groups, or between the STI− and STI+ subgroups of minimal ETE. However, the maximal ETE group had significantly higher recurrence and lower survival rates than the other groups (P < 0.001).

Conclusion

Maximal ETE is a significant factor for poor prognosis. However, minimal ETE is not associated with increased recurrence or decreased survival in patients with PTC.

Introduction

Extrathyroidal extension (ETE) is defined as extension of the primary tumor beyond the thyroid capsule into the perithyroidal soft tissues, strap muscles, and adjacent structures [1], [2]. It has been considered an important prognostic factor in papillary thyroid carcinoma (PTC) although there are many others, such as age and sex of patients, primary tumor size, lymph node metastasis, and distant metastasis [1], [2], [3], [4], [5], [6]. ETE is included in almost all prognostic classification systems, such as EORTC (European Organization for Research and Treatment of Cancer), MACIS (metastasis, age, completeness of resection, invasion, and size), AMES (age, metastasis, ETE, and size), AGES (age, grade, ETE, and size), and the AJCC (American Joint Committee on Cancer) TNM staging system [7], [8], [9], [10], [11].

In general, ETE has been reported as an adverse prognostic factor for survival and recurrence of PTC. Some authors found that it was associated with low survival and high recurrence rates [1], [12], although others found that it did not adversely influence tumor behavior or survival in patients with PTC or follicular thyroid carcinoma [13].

ETE can be categorized as microscopic or macroscopic depending on the extent of invasion. It has been reported that the outcome of macroscopic gross ETE was worse than that of microscopic local invasion [14], [15], [16], [17]. However, in the previous studies the definition of ETE was neither clear nor constant. The terms minimal ETE and maximal ETE have also been used inconsistently in many previous studies, so that it is somewhat difficult to interpret the results.

In particular, although maximal ETE is considered a factor for poor prognosis, the significance of minimal ETE has not been clearly established. Some studies have shown that microscopic ETE alone does not have a significant impact on oncologic outcomes [15], [18], [19], though in another study its significance was undetermined [16]. Other authors have reported that the 20-year overall survival rate with microscopic ETE did not differ from macroscopic ETE [2].

The aim of this study was to investigate the clinicopathologic characteristics and prognostic significance of ETE in patients with PTC, in relation to the degree of ETE, particularly minimal vs maximal ETE.

Section snippets

Patients

The medical records of 967 patients who underwent thyroidectomy for PTC between January 2000 and December 2011 were studied retrospectively. The exclusion criteria were recurrent cases, other types of malignancy, concurrent PTC and other types of malignancy, and cases with follow-up of less than 24 months. Informed consent was obtained from each patient and the study was approved by the Institutional Review Board of Hanyang University Hospital.

Patients were categorized into three groups

Results

Among 967 patients with PTC, 491 (50.8%) had no ETE, 403 (41.7%) had minimal ETE, and 73 (7.5%) had maximal ETE. The STI+ and STI− subgroups of the 403 patients with minimal ETE comprised 121(30.0%) and 282 (70.0%) patients, respectively. All patients of the STI+ subgroup showed invasion only to the sternothyroid muscle. In the maximal ETE group, the most commonly involved structures were the recurrent laryngeal nerve (49 cases), trachea (36 cases), esophagus (15 cases), and larynx (13 cases),

Discussion

Extrathyroidal extension is a well-known and significant factor for poor prognosis in patients with PTC. The prevalence of ETE in PTC varies from 5% to 55.3%, and larger tumors are associated with an increased likelihood of ETE [1], [3], [18], [20], [21], [22]. In the present study, ETE was found in 49.2% (minimal ETE 41.7%, maximal ETE 7.5%) of patients with PTC, which is comparable to findings in other studies.

The clinical implications of ETE for the staging of thyroid cancer have changed

Conclusions

Maximal ETE is an important factor for poor prognosis due to a higher rate of recurrence and decreased survival. However, minimal ETE, regardless of strap muscle invasion, does not correlate with increased recurrence or decreased survival in patients with PTC if treated appropriately.

Conflict of interest

None of the authors have any conflicts of interest regarding the content of this article.

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