Characteristics and significance of minimal and maximal extrathyroidal extension in papillary thyroid carcinoma
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.
References (27)
- et al.
Extrathyroid spread in papillary carcinoma of the thyroid: clinicopathological and prognostic study
Otolaryngol Head Neck Surg
(2001) - et al.
Differentiated carcinoma of the thyroid with extrathyroidal extension
Am J Surg
(1995) - et al.
Local control in differentiated thyroid carcinoma with extrathyroidal invasion
Am J Surg
(2000) - et al.
Prognostic factors in differentiated carcinoma of the thyroid gland
Am J Surg
(1992) - et al.
Early death from papillary thyroid carcinoma
Am J Otolaryngol
(2012) - et al.
A prognostic index for thyroid carcinoma: a study of the E.O.R.T.C. Thyroid Cancer Cooperative Group
Eur J Cancer
(1979) - et al.
Long-term impact of initial surgical and medical therapy on papillary and follicular thyroid cancer
Am J Med
(1994) - et al.
Implication of minimal extrathyroidal extension as a prognostic factor in papillary thyroid carcinoma
Int J Surg
(2013) - et al.
Locally advanced differentiated thyroid cancer
Surg Oncol
(2003) - et al.
Extrathyroidal extension in well-differentiated thyroid cancer: macroscopic vs microscopic as a predictor of outcome
Arch Otolaryngol Head Neck Surg
(2007)
Ipsilateral lobectomy versus bilateral lobar resection in papillary thyroid carcinoma: a retrospective analysis of surgical outcome using a novel prognostic scoring system
Surgery
An expanded view of risk-group definition in well differentiated thyroid carcinoma
Surgery
Predicting outcome in papillary thyroid carcinoma: development of a reliable prognostic scoring system in a cohort of 1779 patients surgically treated at one institution during 1940 through 1989
Surgery
Cited by (60)
Predictive value of ultrasonic features and microscopic extrathyroidal extension in the recurrence of PTC
2022, European Journal of RadiologyDoes macroscopic extrathyroidal extension to the strap muscles alone affect survival in papillary thyroid carcinoma?
2022, Surgery (United States)Citation Excerpt :Extrathyroidal extension (ETE) in papillary thyroid carcinoma (PTC) can be found as gross disease intraoperatively or incidentally as microscopic ETE (microETE) on histopathology review. The overall impact of macroscopic ETE (macroETE) in PTC is well known and is recognized as a predictor of recurrence and disease-specific death.1–3 On the other hand, the current literature on microETE and its role in PTC is inconsistent.
Papillary Thyroid Cancer
2021, Surgery of the Thyroid and Parathyroid GlandsExtrathyroidal extension predicts negative clinical outcomes in papillary thyroid cancer
2021, Surgery (United States)Significance of multifocality in papillary thyroid carcinoma
2020, European Journal of Surgical Oncology