The Relationship of BrafV600E Mutation Status to FDG PET/CT Avidity in Thyroid Cancer: A Review and Meta-Analysis

Objective: Papillary thyroid cancer (PTC) harboring a BRAF^V600E gene mutation has been shown to exhibit aggressive tumor behavior and carries higher risks of recurrence and disease-specific death. In this systematic review and meta-analysis, we examined published evidence related to the accuracy of fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) in detection of residual disease in patients with BRAF^V600E mutated thyroid cancer.Methods: We extracted data from PUBMED/MEDLINE and EMBASE published between January 1995 and March 2017. We included studies that compared FDG PET standardized uptake values (SUVs) between BRAF^V600E-positive and BRAF^V600E-negative subjects, as well as those that evaluated the odds of having FDG avidity between BRAF^V600E-positive and -negative patients with thyroid cancer.Results: There were a total of 12 studies in the systematic review. Seven studies qualified for the analysis for calculating the pooled odds ratio (OR). The pooled cohort with binary data had 1,144 patients out of which 843 were BRAF^V600E positive and 301 were BRAF^V600E negative. Those with a BRAF^V600E mutation had a significantly greater likelihood of having FDG-avid lesions. The pooled OR was 2.12 (confidence interval &lsqb;CI] 1.53–3.00, P<.01). The pooled mean SUV (cohort of 315 patients) was significantly higher in BRAF^V600E-positive compared to BRAF^V600E negative patients, with a pooled mean difference of 5.1 (CI 4.3–5.8).Conclusion: Our meta-analysis shows that presence of BRAF^V600E mutation in PTC confers a higher likelihood of FDG PET avidity and is associated with higher SUV uptake values compared to BRAF^V600E-mutation negative status.Abbreviations: BRAF = B-Raf proto-oncogene, serine/threonine kinase; CI = confidence interval; CT = computed tomography; DTC = differentiated thyroid cancer; FDG = fluorodeoxyglucose; PET = positron emission tomography; PTC = papillary thyroid cancer; SUV = standardized uptake value     

Molecular pathology and thyroid FNA

This review summarises molecular pathological techniques applicable to thyroid FNA. The molecular pathology of thyroid tumours is now fairly well understood. Molecular methods may be used as a rule‐in test for diagnosis of malignancy in thyroid nodules, eg BRAF V600E point mutation, use of a seven‐gene mutational panel (BRAF V600E, RAS genes, RET/PTC or PAX8/PPARG rearrangement), or as a comprehensive multigene next‐generation sequencing panel, eg ThyroSeq v2. Molecular methods can also be applied as rule‐out tests for malignancy in thyroid nodules, eg Afirma or ThyroSeq v2 or as markers of prognosis, eg TERT promoter mutation or other gene mutations including BRAF V600E, TP53 and AKT1, and as tests for newly defined tumour entities such as non‐invasive follicular thyroid neoplasm with papillary like nuclei, or as a molecular marker(s) for targeted therapies. This review describes practical examples of molecular techniques as applied to thyroid FNA in routine clinical practice and the value of molecular diagnostics in thyroid FNA. It describes the range of molecular abnormalities identified in thyroid nodules and thyroid cancers with some practical applications of molecular methods to diagnosis and prognosis of thyroid nodules and thyroid cancer.     

Thyroid Cytology and Risk of Thyroid Cancer: Differences Among Indeterminate Specimens

ObjectiveTo assess the potential for stratification of indeterminate cytologic findings on fine-needle aspiration (FNA) of thyroid nodules in an effort to improve therapeutic strategies.MethodsWe attempted to determine the malignant risk associated with various indeterminate FNA cytologic patterns by correlation of specimens with the final histologic diagnosis. For this analysis, we identified 294 computerized medical records of surgically treated thyroid nodules during a 5-year period at our institution with the corresponding FNA cytology reports available.ResultsOf the 294 surgical cases, 162 with a positive or indeterminate cytologic report were selected, reviewed, and classified. Of 52 patients with positive cytologic findings on FNA, 51 (98%) had a final histologic report of a malignant thyroid nodule. Of 110 patients with indeterminate specimens, 30 (27%) had a final histologic diagnosis of thyroid carcinoma. The presence of nuclear atypia was predictive of thyroid carcinoma in 75% of patients, a Hürthle cell cytologic pattern was associated with a malignant thyroid nodule in 33%, and a hypercellular smear was suggestive of malignant involvement in 26% of cases. The lowest rate of malignant potential was associated with cytologic microfollicular and scant colloid alone subtype (6%).ConclusionThe results of this study show that indeterminate thyroid cytologic specimens can be subdivided into groups with different malignant risks. A microfollicular cytologic pattern in the absence of a hypercellular smear or nuclear atypia does not support a recommendation of surgical treatment. A malignant cytologic diagnosis has a high positive predictive value for detection of thyroid cancer. (Endocr Pract. 2004;10:330-334)     

The BRAF mutation confers sensitivity of thyroid cancer cells to the BRAF inhibitor PLX4032 (RG7204)

Aberrant signaling of the Ras-Raf-MEK-ERK (MAP kinase) pathway driven by the mutant kinase BRAF^V600E, as a result of the BRAF^T1799A mutation, plays a fundamental role in thyroid tumorigenesis. This study investigated the therapeutic potential of a BRAF^V600E-selective inhibitor, PLX4032 (RG7204), for thyroid cancer by examining its effects on the MAP kinase signaling and proliferation of 10 thyroid cancer cell lines with wild-type BRAF or BRAF^T1799A mutation. We found that PLX4032 could effectively inhibit the MAP kinase signaling, as reflected by the suppression of ERK phosphorylation, in cells harboring the BRAF^T1799A mutation. PLX4032 also showed a potent and BRAF mutation-selective inhibition of cell proliferation in a concentration-dependent manner. PLX4032 displayed low IC₅₀ values (0.115–1.156 μM) in BRAF^V600E mutant cells, in contrast with wild-type BRAF cells that showed resistance to the inhibitor with high IC₅₀ values (56.674–1349.788 μM). Interestingly, cells with Ras mutations were also sensitive to PLX4032, albeit moderately. Thus, this study has confirmed that the BRAF^T1799A mutation confers cancer cells sensitivity to PLX4032 and demonstrated its specific potential as an effective and BRAF^T1799A mutation-selective therapeutic agent for thyroid cancer.     

Associations of the BRAFV600E Mutation with Sonographic Features and Clinicopathologic Characteristics in a Large Population with Conventional Papillary Thyroid Carcinoma

Objective

To evaluate the association of the BRAF^V600E mutation with sonographic features and clinicopathologic characteristics in a large population with conventional papillary thyroid carcinoma (PTC).

Methods

We retrospectively reviewed the sonographic features, clinicopathologic characteristics, and presence of the BRAF^V600E mutation in 688 patients who underwent thyroidectomy for conventional PTC between January and July 2010 at a single institution. The incidence of the BRAF^V600E mutation was calculated. The sonographic features and clinicopathologic characteristics were compared between BRAF-positive and BRAF-negative patients. BRAF-positive patients were subdivided into those with papillary thyroid microcarcinoma (the PTMC group) and those with PTC larger than 10 mm (the PTC>10 mm group), and their sonographic features were compared.

Results

The BRAF^V600E mutation was detected in 69.2% of patients (476 of 688). Sonographic features were not significantly different between BRAF-positive and BRAF-negative PTC, nor between PTMC and PTC>10 mm groups. The BRAF^V600E mutation was associated with male sex (P = 0.028), large tumor size, extrathyroidal extension, central and lateral lymph node metastasis, and advanced tumor stage (P<0.0001).

Conclusion

The BRAF^V600E mutation was significantly associated with several poor clinicopathologic characteristics, but was not associated with sonographic features, regardless of tumor size. We recommend that patients with a thyroid nodule with any suspicious sonographic feature undergo preoperative BRAF^V600E testing for risk stratification and to guide the initial surgical approach in PTC.     

Is Follow-up BRAFV600E Mutation Analysis Helpful in the Differential Diagnosis of Thyroid Nodules with Negative Results on Initial Analysis?

Background

We evaluated the usefulness of follow-up BRAF^V600E mutation analysis using ultrasonography-guided fine-needle aspiration (US-FNA) in diagnosis of thyroid nodules showing negative BRAFV600E mutation on prior analysis.

Methodology/Principal Finding

A total of 49 patients (men: 6, women: 43, mean age: 50.4 years) with 49 thyroid nodules were included. Patients had undergone initial and follow-up US-FNA and subsequent BRAF^V600E mutation analysis from US-FNA aspirates. All patients had negative results on initial BRAF^V600E mutation analysis. Clinicopathologic findings, US assessment, and BRAF^V600E mutation results were analyzed according to the final pathology. Of the 49 nodules, 12 (24.5%) were malignant and 37 (75.5%) were benign. Seven (58.3%) of the 12 malignant nodules were positive for BRAF^V600E mutation on follow-up, all showing suspicious US features. Initial US-FNA cytology of the 7 nodules were non-diagnostic (n = 2), benign (n = 2), or atypia (n = 3), while follow-up were benign (n = 1), indeterminate (n = 1), suspicious for malignancy (n = 4), and malignancy (n = 1).

Conclusions/Significance

Follow-up BRAF^V600E mutation analysis may be helpful in the diagnosis of selected thyroid nodules negative for BRAF^V600E mutation on initial analysis, which are assessed as suspicious malignant on US, diagnosed as non-diagnostic, benign or atypia on follow-up US-FNA.     

Overview of Molecular Biomarkers for Enhancing the Management of Cytologically Indeterminate Thyroid Nodules and Thyroid Cancer

ObjectiveTo provide information on molecular bio markers that can help assess cytologically indeterminate thyroid nodules.MethodsPublished studies on immunohistologic, somatic mutation, gene expression classifier, microRNA, and thyrotropin receptor messenger RNA biomarkers are reviewed, and commercially available molecular test pan els are described.ResultsThyroid nodules are common, and clinical guidelines delineate an algorithmic approach including serum thyroid-stimulating hormone measurement, diagnostic ultrasound examination, and, when appropriate, fine-needle aspiration (FNA) biopsy for determination of a benign versus malignant status. In clinical practice, approximately 20% of FNA-derived cytology reports are classified as “indeterminate” or follicular nodules that do not fulfill either benign or malignant criteria. In this set ting, the actual risk for malignancy of a cytologically indeterminate nodule ranges from approximately 15% to 34%. Research describing molecular biomarkers from thyroid cancer tissue has been applied to FNA-derived thyroid nodule material. There is also a serum molecular marker that has been reported with goals similar to those for the FNA-derived molecular markers: to enhance the preoperative diagnosis of thyroid cancer and reduce the large number of patients who have a diagnostic surgical procedure for benign thyroid nodules.ConclusionProgress toward the foregoing goals has been made and continues to evolve with the recent appearance of molecular biomarker tests that can be selectively applied for further assessment of cytologically indeterminate thyroid nodules. (Endocr Pract. 2012;18:611-615)     

Hypermethylated RASSF1 and SLC5A8 promoters alongside BRAFV600E mutation as biomarkers for papillary thyroid carcinoma

Circulating cell-free DNA (cfDNA) has been considered as a diagnostic source to track genetic and epigenetic alterations in cancer. We aimed to study mutation in addition to the methylation status in the promoter regions of RASSF1 and SLC5A8 genes in tissues and circulating free DNA samples of patients affected with papillary thyroid carcinoma (PTC) and thyroid nodules as controls. BRAF^V600E mutation was studied by ARMS-scorpion real-time polymerase chain reaction method in 57 PTC and 45 thyroid nodule cases. Methylation status of RASSF1 and SLC5A8 promoter regions was analyzed by methylation-specific high-resolution melting curve analysis. BRAF^V600E mutation was found in 39 (68.4%) out of 57 PTC tissue samples, while in 33 (49.1%) cases of cfDNA, this mutation was detected. The frequency of BRAF^V600E mutation in cfDNA was significantly different between metastatic and nonmetastatic PTC cases (22 of 33 PTC cases vs. 5 of 34 thyroid nodule samples). Methylation levels of three promoter regions of SLC5A8 and proximal promoter region of RASSF1 was significantly different between PTC and thyroid nodule cases in both cfDNA and tissue DNA. In addition, the methylation status of these two genes in tissue DNA was reflected in methylation status observed in cfDNA. This study confirmed that BRAF^V600E mutation is better for discrimination between papillary thyroid carcinoma and thyroid nodules. On the other hand, hypermethylation in the more proximal promoter regions to RASSF1 and SLC5A8 genes showed higher sensitivity and more acceptable specificity for this discrimination.     

Thyroseq®V2.0 Molecular Testing: A Cost-Effective Approach for the Evaluation of Indeterminate Thyroid Nodules

Objective: Approximately 15 to 30% of thyroid nodules have indeterminate cytology. Many of these nodules are treated surgically, but only 5 to 30% are malignant. Molecular testing can further narrow the risk of malignancy of these nodules. Our objective was to assess the cost effectiveness of ThyroSeq®V2.0 compared to diagnostic thyroidectomy for the evaluation of indeterminate nodules.Methods: Cytology and histopathology slides of Bethesda category III and IV (suspicious for follicular neoplasia [SFN]) nodules obtained between January 1, 2014 and November 30, 2016 were re-reviewed by 2 endocrine cytopathologists. Costs for a diagnostic approach using ThyroSeq® were calculated and compared to those of diagnostic thyroidectomy.Results: We included 8 Bethesda category III nodules that underwent ThyroSeq® and 8 that underwent diagnostic surgery. Of those submitted for ThyroSeq®, 4 were positive for mutations and underwent thyroid surgery. The average cost per nodule evaluated was $14,669 using ThyroSeq®, compared to $23,338 for diagnostic thyroid surgery. The cost per thyroid cancer case detected was $58,674 using ThyroSeq® compared to $62,233 for diagnostic thyroid surgery. We included 13 nodules Bethesda category IV that underwent ThyroSeq® and 11 that underwent diagnostic surgery. Of those submitted for ThyroSeq®, 6 were positive for mutation and underwent thyroid surgery. The average costs per nodule evaluated were $14,641 using ThyroSeq® and $24,345 using diagnostic thyroidectomy. The cost per thyroid cancer case detected was $31,721 when using ThyroSeq® compared to $53,560 for diagnostic thyroidectomy.Conclusion: The use of ThyroSeq® in our institution is cost effective compared to diagnostic thyroid surgery for the evaluation of Bethesda categories III and IV (SFN) nodules.Abbreviations: FNA = fine-needle aspiration; GEC = gene expression classifier; NIFTP = noninvasive follicular thyroid neoplasm with papillary-like nuclear features; PTC = papillary thyroid cancer; SFN = suspicious for follicular neoplasia     

Bisphenol A at a human exposed level can promote epithelial-mesenchymal transition in papillary thyroid carcinoma harbouring BRAFV600E mutation

Bisphenol A (BPA), a ubiquitous endocrine-disrupting chemical, alters the function of endocrine system and enhances the susceptibility to tumorigenesis in several hormone-dependent tumours as thyroid carcinoma. About 50% of papillary thyroid cancers (PTC), the most common type of thyroid malignancy, harbours the BRAF^V600E mutation. This study aimed to investigate a potential combined effect of BPA exposure and BRAF^V600E mutation on epithelial-mesenchymal transition (EMT) in PTC. Firstly, the level of BPA in plasma, the evaluation of BRAF^V600E mutation and the level of EMT-related proteins in PTC samples were individually determined. Additionally, the migration, invasion, colony formation capacity and the expression of EMT-related proteins after exposure to BPA were precisely analysed in vitro thyroid cells genetically modified by the introduction of BRAF^V600E mutation. Moreover, ERK-Cox2 signalling pathway was also introduced to explore the possible mechanism in PTC development. As expected, whether the clinical investigation or cultured thyroid cells demonstrated that BPA at a concentration compatible with human exposed levels (10^-7 M) synergized with the BRAF^V600E mutation promoted EMT via the activation of ERK-Cox2 signalling pathway. Our findings offer some evidence that BPA as an environmental risk factor can facilitate the progression of PTC harbouring BRAF^V600E mutation.     

Allele-Specific PCR with Competitive Probe Blocking for Sensitive and Specific Detection of BRAF V600E in Thyroid Fine-Needle Aspiration Specimens

Objective: To detect BRAF V600E mutation in thyroid fine-needle aspiration (FNA) slides and needle rinses (NR). Study Design: Tumor-enriched DNA was extracted from FNA smears, formalin-fixed paraffin-embedded (FFPE) sections, or NR specimens from 37 patients with confirmed papillary thyroid carcinoma or benign findings. An allele-specific primer selectively amplified the 1799 T>A BRAF mutation while simultaneously blocking amplification of wild-type (WT) BRAF with an unlabeled probe during PCR. Mutation detection was accomplished by melting analysis of the probe. Results: Allele-specific/blocking probe PCR confirmed the BRAF mutation status for 20 of 24 paired FNA/FFPE samples previously tested by fluorescent probe real-time PCR. For the other 4 cases, the sensitive PCR method detected the BRAF mutation in all paired FNA/FFPE samples. Previously, the mutation had been detected in only the FFPE samples. The BRAF mutation was also detected in some NR specimens. Conclusion: Treatment of patients with thyroid nodules is guided by FNA biopsy, which can be scantly cellular, necessitating a sensitive test that can detect low levels of BRAF V600E mutation in a WT background. We report increased detection of BRAF V600E in FNA specimens using allele-specific/blocking probe PCR, which has an analytical sensitivity of 0.01%.     

Focus: Personalized Medicine: Simultaneously Detection of 50 Mutations at 20 Sites in the BRAF and RAS Genes by Multiplexed Single-Nucleotide Primer Extension Assay Using Fine-Needle Aspirates of Thyroid Nodules

Fine-needle aspiration (FNA) is commonly used for primary evaluation of thyroid nodules. Twenty to 30 percent of thyroid nodules remain indeterminate after FNA evaluation. Studies show the BRAF p.V600E to be highly specific for papillary thyroid carcinoma (PTC), while RAS mutations carry up to 88 percent positive predictive value for malignancy. We developed a two-tube multiplexed PCR assay followed by single-nucleotide primer extension assay for simultaneous detection of 50 mutations in the BRAF (p.V600E, p.K601E/Q) and RAS genes (KRAS and NRAS codons 12, 13, 19, 61 and HRAS 61) using FNA smears of thyroid nodules. Forty-two FNAs and 27 paired formalin-fixed, paraffin-embedded (FFPE) tissues were tested. All BRAF p.V600E-positive FNA smears (five) carried a final diagnosis of PTC on resection. RAS mutations were found in benign as well as malignant lesions. Ninety-two percent concordance was observed between FNA and FFPE tissues. In conclusion, our assay is sensitive and reliable for simultaneous detection of multiple BRAF/RAS mutations in FNA smears of thyroid nodules.     

Identification and synthesis of N-(thiophen-2-yl) benzamide derivatives as BRAFV600E inhibitors

The V600E BRAF kinase mutation, which activates the downstream MAPK signaling pathway, commonly occurs in about 8% of all human malignancies and about 50% of all melanomas. In this study, we employed virtual screening and chemical synthesis to identify a series of N-(thiophen-2-yl) benzamide derivatives as potent BRAF^V600E inhibitors. Structure–activity relationship studies of these derivatives revealed that compounds b40 and b47 are the two most potent BRAF^V600E inhibitors in this series.     

Intra- and inter-tumor heterogeneity of BRAF(V600E))mutations in primary and metastatic melanoma

The rationale for using small molecule inhibitors of oncogenic proteins as cancer therapies depends, at least in part, on the assumption that metastatic tumors are primarily clonal with respect to mutant oncogene. With the emergence of BRAF^V600E as a therapeutic target, we investigated intra- and inter-tumor heterogeneity in melanoma using detection of the BRAF^V600E mutation as a marker of clonality. BRAF mutant-specific PCR (MS-PCR) and conventional sequencing were performed on 112 tumors from 73 patients, including patients with matched primary and metastatic specimens (n = 18). Nineteen patients had tissues available from multiple metastatic sites. Mutations were detected in 36/112 (32%) melanomas using conventional sequencing, and 85/112 (76%) using MS-PCR. The better sensitivity of the MS-PCR to detect the mutant BRAF^V600E allele was not due to the presence of contaminating normal tissue, suggesting that the tumor was comprised of subclones of differing BRAF genotypes. To determine if tumor subclones were present in individual primary melanomas, we performed laser microdissection and mutation detection via sequencing and BRAF^V600E-specific SNaPshot analysis in 9 cases. Six of these cases demonstrated differing proportions of BRAF^V600Eand BRAF^wild-type cells in distinct microdissected regions within individual tumors. Additional analyses of multiple metastatic samples from individual patients using the highly sensitive MS-PCR without microdissection revealed that 5/19 (26%) patients had metastases that were discordant for the BRAF^V600E mutation. In conclusion, we used highly sensitive BRAF mutation detection methods and observed substantial evidence for heterogeneity of the BRAF^V600E mutation within individual melanoma tumor specimens, and among multiple specimens from individual patients. Given the varied clinical responses of patients to BRAF inhibitor therapy, these data suggest that additional studies to determine possible associations between clinical outcomes and intra- and inter-tumor heterogeneity could prove fruitful.     

Surgical Utility of Afirma: Effects of High Cancer Prevalence and Oncocytic Cell Types in Patients with Indeterminate Thyroid Cytology

ObjectiveThe Afirma Gene Expression Classifier (GEC) molecular marker assay was developed for the purpose of improving surgical decision-making with indeterminate fine-needle aspiration (FNA) biopsies of thyroid nodules. In this paper, we analyze the performance of the GEC over 27 months in a community hospital-based thyroid surgery practice.MethodsWe began using GEC and Thyroid Cytopathology Partners (TCP) exclusively for thyroid FNA analysis in January 2011, shortly after the Afirma GEC became commercially available. In this paper, we focus on patients with indeterminate FNA results and the outcomes of GEC analysis, with particular attention paid to the calculation of the negative predictive value (NPV) of the Afirma test.ResultsWe performed 645 FNAs in 519 patients over 27 months. Overall, 58 FNAs (9%) were read as indeterminate, with 36 of these classified as suspicious by GEC (62%), 20 characterized as GEC benign (34%), and 2 determined to be inadequate due to low mRNA content. Of the 36 suspicious GEC patients, 30 underwent thyroidectomy, and 21 of the 30 had malignant final pathology. Of the 20 benign GEC patients, 5 underwent thyroid surgery, and 2 were discovered to have malignancies. The NPV for the Afirma GEC in our practice environment was 89.6%.ConclusionIn a practice with a high incidence of thyroid cancer in patients with indeterminate FNAs (33% for our practice), the NPV of the Afirma GEC test may not be as robust as suggested in the existing literature. (Endocr Pract. 2014;20:364-369)     

A modified screening strategy for Lynch syndrome among MLH1-deficient CRCs: Analysis from consecutive Chinese patients in a single center

BackgroundThe low prevalence of the BRAF V600E mutation in colorectal cancers (CRCs) in Chinese populations has stimulated concern about the efficacy of BRAF mutation analysis for Lynch syndrome (LS) screening.MethodsIn total, 169 of 4104 consecutive CRC patients with absent MLH1 staining were analyzed to compare the utility of the BRAF V600E mutation testing with MLH1 promoter methylation analysis in the Chinese population. Germline genetic testing was performed in patients with wild-type BRAF/methylated MLH1.ResultsCompared with BRAF genotyping, the use of MLH1 methylation testing alone to evaluate patients with MLH1 deficiency reduced referral rates for germline testing by 1.8-fold (82.8% vs. 47.1%). However, 6 patients harboring MLH1 promoter methylation were verified to have LS through germline genetic testing. It is notable that all 6 patients had a family history of CRC in at least 1 first-degree relative (FDR) or second-degree relative (SDR). The combination of MLH1 promoter methylation analysis and a family history of CRC could preclude significantly more patients from germline genetic testing than from BRAF mutation testing alone (45.5% vs. 17.2%, p<0.001) and decrease the number of misdiagnosed LS patients with MLH1 promoter methylation.ConclusionThe combination of a family history of CRC with MLH1 promoter methylation analysis showed better performance than BRAF mutation testing in the selection of patients in the Chinese population for germline genetic testing.     

Tumor Location Is Associated With the Prevalence of Braf And Pik3ca Mutations in Patients with Wild-Type Ras Colorectal Cancer: A Prospective Multi-Center Cohort Study in Japan

BACKGROUND: Primary tumor location is a critical prognostic factor that also impacts the efficacy of anti-epidermal growth factor receptor (EGFR) therapy in wild-type RAS (KRAS/NRAS) metastatic colorectal cancer (CRC). However, the association between the incidence of BRAF and phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA) mutations and primary tumor location remains unclear. METHODS: We prospectively collected tumor samples and clinical data of patients from 15 hospitals between August 2014 and April 2016 to investigate RAS, BRAF, and PIK3CA mutations using a polymerase chain reaction-based assay. According to the primary tumor location, patients were classified to right-sided (from cecum to splenic flexure) and left-sided (from descending colon to rectum) tumor groups. RESULTS: In total, 577 patients with CRC were investigated, 331 patients (57%) had CRC with wild-type RAS; of these 331 patients, 10.5%, 4.8%, and 5.9% patients harbored BRAF^V600E, BRAF^non-V600E, and PIK3CA mutations, respectively. BRAF/PIK3CA mutations were more frequent in females, patients with right-sided tumors, and patients with peritoneal metastasis cases and less frequent in patients with liver metastases. The prevalence rates of BRAF^V600E and PIK3CA mutations were higher in patients with right-sided tumors than in those with left-sided tumors (32.3% vs. 4.8% and 17.2% vs. 3.6%, respectively). CONCLUSIONS: More than half of the patients with right-sided CRC and wild-type RAS harbored BRAF/PIK3CA mutations, including BRAF^non-V600E, which may contribute to the difference in the anti-EGFR efficacy between the right- and left-sided CRC.