Encapsulated follicular variant of papillary thyroid cancer: are these tumors really benign?

Abstract

Background

Recent studies suggest that the encapsulated form of follicular variant of papillary thyroid cancer (eFVPTC) behaves more similarly to benign lesions and can be treated with thyroid lobectomy alone instead of total thyroidectomy. To distinguish aggressive cancers from more benign lesions more clearly, the objective of this study was to determine if the eFVPTC behaves less aggressively than the nonencapsulated variant (neFVPTC).

Methods

A prospectively collected endocrine surgery database in our institution was reviewed for all patients with FVPTC on surgical pathology from 1999 to 2012. Samples were rereviewed to determine if the tumor was eFVPTC or neFVPTC, which were correlated with patient outcomes.

Results

Of the 68 patients, 59 (87%) had eFVPTC and 9 (13%) had neFVPTC. The mean age was 48 y and 63% were female. Fifty-four of 64 patients (84%) who had a total thyroidectomy received radioactive iodine. The eFVPTC group had lower rates of cervical LN involvement (5% versus 22%, P = 0.2504). The median follow-up time was 3 y (0-13 y) and only two patients had recurrence, one with eFVPTC and one with neFVPTC. None of the patients had distant metastasis or died of their disease.

Conclusions

eFVPTCs appear to have a lower rate of cervical lymph node metastases compared with neFVPTCs, but recurrent disease may be seen in both subtypes. These findings suggest eFVPTC can be managed more conservatively.

Introduction

The incidence of thyroid cancer has tripled since 1975.¹ Most of the rise is attributed to the increase in the diagnosis of papillary thyroid carcinoma (PTC), a differentiated thyroid cancer with a 10-y disease-specific survival of 97%.² The exact cause for the increased incidence of PTC is unknown; however, many attribute it to the improved sensitivity of ultrasound to identify thyroid nodules,1, 3 as well as potential environmental factors.⁴ Furthermore, it is possible that some of the rise is due to some lesions previously classified as follicular adenomas (FAs) now being classified as follicular variant PTC (FVPTC). Mehzrad et al. compared the changes in the incidence of FVPTC with the changes in the incidence of FA.⁵ The study showed that the incidence of FVPTC was increasing while the incidence of FA was decreasing.

Interestingly, although the incidence of thyroid cancers dramatically increased, the mortality has remained the same. We may be diagnosing smaller, more indolent cancers that would not cause symptoms or death, which is leading to overtreatment.¹ It is crucial that we seek factors that can help identify the lack of aggressive features of these cancers so that the side effects of the treatment such as recurrent laryngeal nerve injury, wound infection, hypothyroidism, and hypoparathyroidism can be avoided.6, 7, 8 Recent research shows that encapsulated form of FVPTC (eFVPTC) without invasion has an excellent prognosis with virtually no recurrence.9, 10, 11 This observation leads to the change of FVPTC classification–noninvasive, eFVPTCs with certain additional features were reclassified to be “noninvasive follicular thyroid neoplasm with papillary-like nuclear features, or NIFTP.”⁹ To provide more details about different histologic variants, we retrospectively analyzed data. Outcomes of the clinical characteristics of eFVPTC versus nonencapsulated FVPTC (eFVPTC and neFVPTC, respectively) were recorded.

Before the introduction of the newest American Thyroid Association guidelines¹² where solitary thyroid cancers up to 4 cm may be treated with lobectomy alone, most FVPTCs >1 cm were managed similarly to classic PTC with a total thyroidectomy. However, several recent studies suggest that the two histologic variants of FVPTC behave differently, with eFVPTC acting more like a benign lesion, and thus may be managed differently.10, 11, 13 It has been shown that not only histologic phenotype but molecular signatures are also different.¹⁴ The objective of this study was to determine if the eFVPTC behaves less aggressively than the neFVPTC to justify the proposed differences in management. In addition, we further looked at the eFVPTC to determine if there were other features of aggressiveness, such as vascular or capsular invasion.