Clinicopathologic Implications of the BRAF V600E Mutation in Papillary Thyroid Cancer: A Subgroup Analysis of 3130 Cases in a Single Center

Abstract

Background:

The BRAF mutation has been shown to be associated with aggressive clinicopathologic characteristics of papillary thyroid cancer (PTC). However, several studies that analyzed hundreds of patients have not demonstrated any correlation. The objective of this study was to investigate the relationship of the BRAF mutation with clinicopathologic factors in a large group of homogenous PTC patients.

Methods:

We collected data of PTC patients who received curative resection of the thyroid gland and who had undergone BRAF mutation tests of their thyroid cancer tissue. Minor variant PTCs and mixed-type thyroid cancers were excluded in this analysis. Clinicopathologic characteristics, including age, sex, BRAF mutation, tumor histology, size, extrathyroidal extension, tumor margin, lymph node metastasis, multifocality, stage, and associated thyroid disease, were collected. The relationship of the BRAF mutation with clinicopathologic factors was analyzed in each homogenous histologic PTC.

Results:

There were 3130 PTC patients who met the criteria, and these patients were divided into three major histologic groups: conventional PTC (n=2947), diffuse sclerosing variant PTC (n=98), and follicular variant PTC (n=85). The BRAF mutation was variably detected in 75.3%, 61%, and 40% of patients, respectively. In conventional PTC cases, the BRAF mutation was significantly associated with large tumor size, extrathyroidal extension, and lymph node metastasis. Coexistent chronic lymphocytic thyroiditis was significantly less prevalent in the BRAF mutant group. Age, sex, and tumor margin status were not significantly correlated with the BRAF status. There was no evidence that any clinicopathologic factors were linked with the BRAF mutation status in diffuse sclerosing and follicular variant PTCs.

Conclusions:

The BRAF mutation was differentially detected in each histologic subtype of PTC and was strongly correlated with pathologic factors, most strongly with no coexistent chronic lymphocytic thyroiditis, in conventional PTC. The BRAF mutation is suggested to be a poor prognostic marker in conventional PTC, and the BRAF mutational analysis may lead to better management for individual PTC patients.

Introduction

T hyroid cancer incidence has been increasing every year, and thyroid cancer is currently the fifth most common malignancy of women in the United States; it is also the most common in Korean women (1,2). Most are papillary thyroid cancers (PTCs), which account for more than 80% of all thyroid cancers (3,4). Most PTCs show favorable outcome and prognostic factors, including age, histology, tumor size, local invasion, and distant metastases (5,6).

Recently, BRAF mutations have been regarded as a probable poor prognosticator or diagnostic marker for PTC. BRAF mutations have been discovered in a variety of human cancers, including malignant melanoma, lung cancer, colorectal cancer, ovarian cancer, and thyroid cancer (7 –10). BRAF mutations of thyroid cancer have been reported in PTC and anaplastic thyroid cancer, but not in follicular thyroid cancer, medullary thyroid cancer, benign thyroid adenomas, or hyperplasia (11,12). These mutations are found in 26–84% of PTCs (13 –16).

BRAF has been shown to initiate thyroid follicular cell transformation in transgenic mice, leading to conventional PTC with frequent local invasion (17). BRAF mutations have been identified in microcarcinomas, supporting the concept that this mutation may be an inducing factor of oncogenesis (18). On the basis that BRAF mutations correlate with extrathyroidal extension and infiltrative variants of PTC, it was suggested that BRAF mutations have an important role in local invasion and therefore constitute a potential target for therapy. It was observed that BRAF mutations preferentially increased the expression of metalloproteinases in cell lines (19).

Recent reports have established a strong association of BRAF mutations with the aggressive clinicopathologic characteristics of PTC, including extrathyroidal extension, lymph node metastasis, histologic subtypes with poor prognosis (e.g., tall cell variant PTC), and advanced stages and recurrence (20,21). Most studies, including meta-analyses, have shown a correlation with at least one poor prognostic factor (22 –25). Conversely, several studies have not shown any correlations, including two studies that analyzed a relatively large number of patients (26,27). The clinical and pathologic implications of BRAF mutations in PTC are, in part, still controversial. Additionally, no study has analyzed the histologic variations of BRAF mutations in a large number of patients and the clinicopathologic parameters associated with BRAF mutations in each variant PTC. Therefore, we investigated the relationship of a BRAF mutation with clinicopathologic factors in PTCs using large groups of patient data according to histologic subtype.

Materials and Methods

Patients and clinicopathologic data

We used electronic medical records to identify eligible PTC patients in the thyroid cancer center of Gangnam Severance Hospital between June 2009 and July 2012. Patients were included in the study if (i) PTC was their primary tumor, (ii) they had received curative thyroidectomy, and (iii) they had BRAF mutation data of the removed thyroid cancer. The presence of a BRAF mutation was evaluated by restriction fragment length polymorphism (RFLP) or direct sequencing. In case of multifocality, the largest tumor was selected for BRAF testing. We enrolled 3259 patients. All patients underwent total thyroidectomy, unilateral lobectomy, or hemithyroidectomy. Central compartment node dissection was routinely performed, and lateral neck dissection was done in case of abnormality on preoperative imaging or intraoperative examination. Electronic clinical and pathologic records were reviewed to collect the clinicopathologic information: age at initial diagnosis, sex, primary tumor size, tumor involvement (extrathyroidal soft tissue extension vs. intrathyroidal), tumor margin (infiltrative vs. expanding), lymph node metastasis, multifocality, and coexistent thyroid disease. Disease staging was performed according to the criteria outlined by the American Joint Committee for Cancer 2010. The study was approved by the institutional review board of Gangnam Severance Hospital, Yonsei University College of Medicine.

DNA extraction

DNA was extracted from 10-μm-thick sections of paraffin blocks using the QIAamp DNA FFPE Tissue Kit (Qiagen, Hilden, Germany) according to the manufacturer's instructions. DNA was extracted only in tissue obtained from the marked tumor on unstained slides.

BRAF mutation evaluation by direct sequencing

BRAF exon 15, which contains the codon encoding the V600E mutation, was amplified with the following primer pair: forward 5′ ATG CTT GCT CTG ATA GGA A 3′ and reverse 5′ TAA AAA CCG GGA CTC TAC G 3′. The polymerase chain reaction (PCR) conditions were as follows: denaturation at 94°C for 5 minutes, followed by 40 cycles of 94°C for 20 seconds, 56°C for 30 seconds, 72°C for 30 seconds, and a final extension step at 72°C for 5 minutes. PCR products were purified using the Exo I/SAP Clean-Up protocol (Hilden, Germany), and direct DNA sequencing was then performed using the 3730 Big Dye Terminator v 3.1 Sequencing Standard (Applied Biosystems, Foster City, CA). Sequence data were analyzed using an ABI 3730 DNA Analyzer (Applied Biosystems). Tumors with a mutant–to–wild-type peak ratio of 15% or more were defined as being heterozygous for the V600E mutation.

BRAF mutation evaluation by PCR-RFLP

The 50 μL PCR mixture was composed of extracted DNA at 100 ng/mL, 5U Taq polymerase, 0.25 mM dNTP, 20 pmol of primers, and 10× Ex Taq buffer. To examine BRAF exon 15, we designed a primer that created a restriction site for the BspE1 enzyme (mismatched forward primer 5′ ATA GGT GAT TTT GGT CTA GCT CCG G 3′ and reverse primer 5′ GAT TTT TGT GAA TAC TGG GAA CT 3′). The PCR conditions were as follows: denaturation at 95°C for 10 minutes, followed by 40 cycles of 94°C for 30 seconds, 45°C for 30 seconds, 72°C for 30 seconds, and a final extension step at 72°C for 10 minutes. The PCR product was purified with the MinElute PCR purification kit (Qiagen) and digested with 10 units of BspE1 (Takara, Tokyo, Japan) at 37°C for 2 hours and electrophoresed in a 4% agarose gel containing ethidium bromide. The stained gel was photographed using a UV light transilluminator. The positive PCR controls were the human PTC cell lines HT29 and ARO, which contain heterozygous BRAF ^V600E mutations, and the negative control was DLD-1, a human papillary carcinoma cell line that harbored only wild-type genetic material.

Statistical analysis

Categorical data were described with frequencies and percentages, and continuous data were described with means/medians and ranges. Statistical comparisons between patient groups were performed using t-tests for parametric variables and the χ²-test for nonparametric variables. Multivariate logistic regression analysis was performed to estimate the odds ratios of clinicopathologic characteristics of PTC for the BRAF mutant group relative to the BRAF wild-type group, independent of other prognostic factors. A p-value <0.05 was considered to be statistically significant. Data were analyzed using IBM SPSS statistics 19 (SPSS Inc., Chicago, IL).

Results

Clinicopathologic characteristics according to histologic types of PTC

We initially enrolled 3259 patients: 2947 patients with conventional PTC, 98 with diffuse sclerosing variant PTC, 85 with follicular variant PTC, and 129 with other variants (tall cell, cribriform-morular, oncocytic, solid, Warthin-like) or mixed-type PTCs. Of the 3259 patients, three major histologic types of PTC, consisting of 3130 cases, were further analyzed (Table 1). The patients with other variant forms of PTC were not separately analyzed because of their small numbers. Bilateral and unilateral total thyroidectomies were performed in 74% and 24% of patients, respectively. The median age of all patients was 45 (range 10–84), and the male-to-female ratio was 1:4 (641:2489). Diffuse sclerosing variant PTC was associated with young (median 36 years old) and male patients compared with conventional and follicular variant PTC (Table 1). The three different histologic PTCs manifested significantly different histopathologic characteristics. Diffuse sclerosing variant PTC was most often associated with poor prognostic pathologies (large tumor size, extrathyroidal extension, infiltrative tumor margin, lymph node metastasis, multifocality; all p<0.05). More than 90% of diffuse sclerosing variant PTC cases presented infiltrative tumor margins and lymph node metastasis. In contrast, follicular variant PTC presented mostly indolent histologic features. Chronic lymphocytic thyroiditis (CLT) was most prevalent (51%) in diffuse sclerosing variant PTC as an associated benign lesion (Table 1).

Table 1.

Clinicopathologic Characteristics of Papillary Thyroid Cancer: Histologic Subtype Analysis

	Conventional (n=2947)		Diffuse sclerosing variant (n=98)		Follicular variant (n=85)
Characteristics	n	%	n	%	n	%
BRAF mutation	2219	75.3	60	61	34	40
Age (years)
Median	45		36		47
Range	13–84		10–74		24–74
Sex, male	598	20.3	29	29.6	14	16.5
Tumor size, (cm)
Mean	0.82		1.5		1
Range	0.05–12.5		0.4–6.2		0.2–6.5
Extrathyroidal extension	1587	53.8	82	83.7	25	29
Tumor margin, infiltrative	2325	78.9	89	90.8	23	27
Lymph node metastasis	1132	38.4	90	91.8	13	15.3
Multifocality	885	30	57	58.1	10	11.8
Coexistence of CLT	964	32.7	50	51	19	22.3

N = 3130.

CLT, chronic lymphocytic thyroiditis.

Of all 3130 cases, the BRAF mutation detection method was done by PCR-RFLP in 231 cases and by direct sequencing in 2899 cases. The results from PCR-RFLP were not validated by sequencing. The BRAF mutation positive rates by each method were 71.8% and 73.7%, respectively, without a significant difference. The BRAF mutation was most commonly detected in conventional PTC (75.3%); follicular variant PTC presented a mutation rate of only 40% (Table 1). As PTCs are composed of heterogeneous histologic subtypes, we analyzed the relationship of the BRAF mutation and clinicopathologic factors within each histologic subtype. Additionally, subgroup analysis was performed to further investigate the relationship of the BRAF mutation with known prognostic factors.

Correlation between the BRAF mutation status and clinicopathologic characteristics in conventional PTC

The BRAF mutation was detected in 75.3% of conventional PTC patients. In the BRAF mutant group, the tumor was larger (0.9 cm vs. 0.7 cm, p<0.001), and extrathyroidal extension (59.2% vs. 43.3%, p<0.001), lymph node metastasis (41.2% vs. 30%, p<0.001), advanced stage (stage III/IV 36.4% vs. 27.7%, p<0.001), and multifocality (31.3% vs. 25.9%, p=0.004) were more prevalent than in the BRAF wild-type group (Table 2). In contrast, coexistent CLT was significantly less common in the BRAF mutant group (28.2% vs. 46.6%, p<0.001). Age, sex, and tumor margin status were not significantly correlated with the BRAF mutation status (Table 2). In a multivariate logistic regression analysis (Table 3), the association of the BRAF mutation with no coexistent CLT, extrathyroidal extension, large tumor size, and lymph node metastasis remained independently significant.

Table 2.

Correlation Between the BRAF Mutation and Clinicopathologic Characteristics in Conventional Papillary Thyroid Cancer

	BRAF positive (n=2219)		BRAF negative (n=728)
Characteristics	n	%	n	%	p
Age (years), median	45		45		0.78
Sex, male	465	21	133	18.3	0.118
Tumor size (cm), mean	0.9		0.7		<0.001^*
Extrathyroidal extension	1283	57.8	305	41.9	<0.001^*
Tumor margin, infiltrative	1760	79.3	565	77.6	0.328
Lymph node metastasis	914	41.2	219	30	<0.001^*
AJCC stage, III/IVA	807	36.4	202	27.7	<0.001^*
Multifocality	696	31.3	189	25.9	0.006^*
Coexistence of CLT	625	28.2	339	46.6	<0.001^*

N = 2947.

Statistically significant, p<0.05.

AJCC, American Joint Committee on Cancer.

Table 3.

Odds Ratios of the BRAF Mutation on Clinicopathologic Characteristics in Patients with Conventional Papillary Thyroid Cancer

Characteristics	Odds ratio	95% confidence interval	p
Without CLT	2.20	1.85–2.63	<0.001
Extrathyroidal extension	1.53	1.25–1.88	<0.001
Tumor size, ≥1cm	1.50	1.20–1.87	<0.001
Lymph node metastasis	1.26	1.04–1.53	0.018
Multifocality	1.18	0.97–1.44	0.096
AJCC stage III/IV	1.08	0.87–1.34	0.466
Tumor margin, infiltrative	1.01	0.81–1.26	0.882

Correlation between the BRAF mutation status and clinicopathologic characteristics in conventional PTC: subgroup analysis according to tumor size

PTC microcarcinomas (<1 cm) are known to be associated with excellent prognosis; they accounted for 72% of tumors in this study. Table 4 summarizes the comparison analysis of microcarcinomas (n=2124) versus macrocarcinomas (n=823). The BRAF mutation was identified more often in macrocarcinomas (72% vs. 83%, p<0.001), and, as might be expected, poor prognostic indicators (extrathyroidal extension, lymph node metastasis, and multifocality) were more closely related with macrocarcinomas (p<0.001). In both groups, the BRAF mutation group presented a higher degree of extrathyroidal extension and lymph node metastasis (p<0.05). Coexistent CLT was significantly less common in the BRAF mutant group (p<0.001). Furthermore, in the microcarcinoma subgroup analysis, the BRAF mutation group was associated with a larger tumor size (p<0.001) and an advanced stage (p=0.001). Overall, the BRAF mutation status of microcarcinomas was more highly associated with aggressive characteristics than that of macrocarcinomas.

Table 4.

Correlation Between the BRAF Mutation Status and Clinicopathologic Characteristics in Conventional Papillary Thyroid Cancer: Subgroup Analysis According to Tumor Size

	Microcarcinoma (n=2124)		Macrocarcinoma (n=823)
Characteristics	n	%	n	%	p
BRAF mutation	1535	72	684	83	<0.001^*
Age (years), median	45		43		0.034^*
Sex, male	408	19.2	190	23.1	0.019^*
Tumor size (cm), mean	0.5		1.3		<0.001^*
Extrathyroidal extension	962	45.3	625	75.9	<0.001^*
Tumor margin, infiltrative	1686	79.4	639	77.6	0.3
Lymph node metastasis	643	30.3	489	59.4	<0.001^*
Multifocality	569	26.8	316	38.4	<0.001^*
Coexistence of CLT	711	33.5	253	30.9	0.17

N = 2947.

Statistically significant, p<0.05.

Correlation between BRAF mutation status and clinicopathologic characteristics in conventional PTC: subgroup analysis according to patient age

As age is a representative prognostic factor and all operable PTC patients who are under 45 years old are considered to be stage I according to the cancer staging system of American Joint Committee on Cancer, the subgroup analysis was performed in two age groups: <45 years old (n=1438) and ≥45 years old (n=1509) (Table 5). There was no significant difference in the BRAF mutation status (75.6% vs. 75%, p=0.71). Older patients manifested more extrathyroidal extensions (p<0.004), infiltrative tumor margins (p=0.042), and multifocality (p=0.004); however, lymph node metastasis was less frequent in this group (p<0.001) than in younger patients. In both groups, the BRAF mutation was strongly associated with large tumor size (p<0.001), extrathyroidal extension (p<0.001), and lymph node metastasis (p<0.05). Coexistent CLT was also significantly less prevalent in the BRAF mutant group (p<0.001). Additionally, in older patients, the BRAF mutation was related to multifocality (p=0.002) and advanced stage (p<0.001).

Table 5.

Correlation Between the BRAF Mutation Status and Clinicopathologic Characteristics in Conventional Papillary Thyroid Cancer: Subgroup Analysis According to Patient Age

	Age <45 years (n=1438)		Age ≥45 years (n=1509)
Characteristics	n	%	n	%	p
BRAF mutation	1087	75.6	1132	75	0.718
Age, median	37		50		<0.001^*
Sex, male	311	21.6	287	19	0.078
Tumor size (cm), mean	0.7		0.7		0.053
Extrathyroidal extension	739	51.4	848	56.2	0.009^*
Tumor margin, infiltrative	1108	77.1	1217	80.6	0.017^*
Lymph node metastasis	646	44.9	486	32.2	<0.001^*
Multifocality	396	27.5	489	32.4	0.004^*
Coexistence of CLT	475	33	489	32.4	0.71

N = 2947.

Statistically significant, p<0.05.

Correlation between coexisting CLT and clinicopathologic characteristics in conventional PTC

As shown in Table 6, CLT was observed in 964 of 2947 conventional PTCs (32.7%) and was associated with a lower prevalence of the BRAF mutation (64.9% vs. 80.3%, p<0.001). Male patients presented less CLT (p<0.001). CLT was associated with more infiltrative tumor margins (p=0.002) and multifocality (p=0.003). However, lymph node metastasis was less common in PTCs with CLT (p=0.012).

Table 6.

Correlation Between the BRAF Mutation Status and Clinicopathologic Characteristics in Conventional Papillary Thyroid Cancer: Subgroup Analysis According

	With CLT (n=964)		Without CLT (n=1983)
Characteristics	n	%	n	%	p
BRAF mutation	626	64.9	1593	80.3	<0.001^*
Age (years), median	45		45		0.51
Sex, male	91	9.4	507	25.6	<0.001^*
Tumor size (cm), mean	0.79		0.83		0.18
Extrathyroidal extension	499	51.8	1088	54.9	0.113
Tumor margin, infiltrative	797	82.7	1528	77.1	<0.001^*
Lymph node metastasis	339	35.2	793	39.9	0.012^*
AJCC stage, III/IVA	311	32.3	698	35.2	0.11
Multifocality	324	33.6	561	28.3	0.003^*

N = 2947.

Statistically significant, p<0.05.

Correlation between the BRAF mutation status and clinicopathologic characteristics in variant PTCs

The BRAF mutation was identified in 61% of diffuse sclerosing variant PTCs and 40% of follicular variant PTCs. No clinicopathologic factors were significantly linked with the BRAF mutation status. Although the BRAF mutation was related with infiltrative tumor margin and less coexistent CLT, there was no statistical significance.

Discussion

Through analyzing data from a large cohort of PTC patients (N=3130) from a single institute, we determined that the presence of a BRAF mutation is a common event in PTC and that its presence was associated with histologic variation. The prevalence of the BRAF mutation was 75.3% in conventional PTCs, 61% in diffuse sclerosing variant PTCs, and 40% in follicular variant PTCs. Additionally, we ascertained that the BRAF mutation was positively associated with tumor size, extrathyroidal extension, and lymph node metastasis, and was inversely related with CLT in conventional PTC. These findings are derived from the largest group of a homogenous patient data set to date. We performed a subgroup analysis of conventional PTC according to age and tumor size. Regardless of age and tumor size, the BRAF mutation was identified in approximately 75% of cases.

Numerous reports on PTCs from several tens or hundreds of patients of various ethnic and geographic backgrounds have demonstrated that BRAF mutations were found in 26–84% of cases (13 –16). This report assures us that the BRAF mutation is prevalent in PTCs (approximately 75% of patients), especially in conventional PTCs in Korea. The BRAF ^V600E mutation is considered to be an inducing factor of the oncogenic transformation in thyroid cancer. It has been determined that BRAF mutation–associated overexpression of various tumor-promoting genes and the silencing of tumor suppressor genes render PTC cells insensitive to radioactive iodine therapy, resulting in persistent cancer or recurrence (22). As frequent subclonal occurrence and heterogeneity of the BRAF mutation presence were observed within PTCs in a recent study (28), further investigation is needed to elucidate the role of BRAF mutations in carcinogenesis and progression.

Previous studies have reported the association of the BRAF mutation with aggressive clinicopathologic characteristics of PTC, such as extrathyroidal extension, lymph node metastasis, and advanced tumor stage (24,25,29 –32). This report of 2947 conventional PTC cases is homogenous and the largest group of data so far, and it reports results that are comparable to numerous previous studies: the BRAF mutation was correlated with tumor size, extrathyroidal extension, and lymph node metastasis. Although some reports indicated that BRAF mutations were more prevalent in older age groups (24,25,29), we did not observe the same result. Several analyses demonstrated that the BRAF mutation is a risk factor for disease persistence or recurrence in PTC (24,25,30 –35). However, we could not verify that observation, as we did not include any follow-up data in this analysis.

Several publications have reported conflicting views regarding the significance of BRAF mutations in PTCs. Ito et al. (26) investigated 631 patients with PTC in Japan and reported that BRAF mutations are not associated with aggressive characteristics and poor prognoses of patients with PTC, even though the incidence of BRAF mutations was significantly higher in macrocarcinomas than in microcarcinomas (40.5% vs. 28.2%, p=0.0175). However, the study had several confounding factors, including limited surgical resection and low rates of postoperative radioactive iodine ablation. Heterogeneity of the BRAF mutation within a tumor and variability of detection methods may also be responsible for the discordant results (36).

BRAF mutations have been identified in several histologic forms of PTC in several studies (24,34,37). The prevalence of BRAF mutations was higher in conventional PTC (51–59%) than in the follicular variant of PTC (17–24%), without reports of the prevalence in diffuse sclerosing variant PTC. In this study, the prevalence rates of the BRAF mutation were 75.3% in 2947 conventional PTCs, 61% in 98 diffuse sclerosing variant PTCs, and 40% in 85 follicular variant PTCs. The variability of the prevalence of the BRAF mutation among the different histological types suggests that differential oncogenic mechanisms might be involved in each PTC subtype. We found that the BRAF mutation was not significantly related to any clinicopathologic parameters in either the diffuse sclerosing or follicular variant PTCs. On the basis of our findings, it is not certain whether the BRAF mutation actually correlates with the aggressiveness of variant PTCs. Future studies on a greater number of patients will be required to elucidate the consequence of BRAF mutations in variant PTCs.

CLT was associated with female sex, infiltrative tumor margins, less lymph node metastasis, and multifocality (all p<0.05). Both favorable and unfavorable pathologic features were correlated with CLT. It has been suggested that CLT may present a predisposition toward the development of PTC (38). However, the autoimmune response to thyroid-specific antigens in CLT is thought to destroy thyroid cancer cells, resulting in lower recurrence and better survival (39). Several clinical reports have demonstrated that CLT is associated with favorable PTC prognosis, female predominance, and multifocality (40 –42). Although the BRAF mutation was detected with a higher frequency in PTCs with no CLT than in PTCs with CLT, the biologic mechanism is not yet known (43). In this study, coexistent CLT was significantly less common in BRAF mutant patients (28.2% vs. 46.6%, p<0.001). Among investigated clinicopathologic factors, no coexisting CLT was most strongly associated with the presence of a BRAF mutation. It is necessary to evaluate the respective roles and the mutual relationship of the BRAF mutation and CLT in the pathogenesis of PTC.

As a limitation of the present study, we could not confirm an independent prognostic role of the BRAF mutation because of the lack of disease persistence/recurrence and survival data. As PTC is a relatively indolent cancer, even though it tends to recur, more than 10 years of follow-up data should be accumulated to evaluate the specific cancer outcome. For future analysis, all enrolled patients should be followed for up to 10–15 years after curative resection. Recently, the percentage of BRAF ^V600E alleles determined by a quantitative assay was identified as a better predictor of clinical outcomes of PTC (36). Therefore, those findings should be considered for the evaluation of the clinical significance of the BRAF mutation in future investigations.

According to the current treatment guidelines, patients with advanced recurrent or metastatic PTC that is not controlled by surgery, radioactive iodine therapy, and radiation are recommended to receive small-molecule kinase inhibitors, including BRAF inhibitors or agents from clinical trials. Unfortunately, treatment strategies customized according to the BRAF mutation status have not yet been established. However, attempts are being made to design therapies that target the pathways responsible for resistance to BRAF and to improve the specificity and potency of BRAF inhibitors. Further exploration of the mechanisms of action or resistance for BRAF-targeted therapies and other multikinase inhibitors in thyroid cancer will be critical.

In conclusion, this large cohort analysis confirms that the BRAF mutation is differentially detected in each variant of PTC and is strongly correlated with unfavorable clinicopathologic factors, especially with no coexisting CLT in conventional PTC. The results suggest that the BRAF mutation should be considered to be a poor prognostic marker in conventional PTC and that the BRAF mutational analysis may lead to a better management for individual PTC patients. To this end, further exploration of the significance of BRAF mutations as a prognostic or predictive biomarker, as a correlating factor with CLT, and as a treatment target in thyroid cancer is mandatory.

Footnotes

Author Disclosure Statement

The authors declare that no competing financial interests exist.

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