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Year : 2019  |  Volume : 56  |  Issue : 2  |  Page : 176--179

Concomitant RAS and BRAF mutation in colorectal cancer - A report of 7 cases

Ozturk Ates1, Suayib Yalcin2,  
1 Department of Medical Oncology, Health Sciences University, Dr. A.Y. Ankara Oncology Hospital, Ankara, Turkey
2 Department of Medical Oncology, Hacettepe University Cancer Institute, Ankara, Turkey

Correspondence Address:
Ozturk Ates
Department of Medical Oncology, Health Sciences University, Dr. A.Y. Ankara Oncology Hospital, Ankara
Turkey

Abstract

Rat sarcoma viral oncogene homolog (RAS) and B-Raf murine sarcoma viral oncogene homolog B1 (BRAF) are members of the same signaling pathway (RAS-RAF-mitogen-activated protein kinase (MAPK) in colorectal cancer (CRC). It is generally assumed that BRAF mutations are seen only with wild-type RAS in CRC. But RAS and BRAF are not mutually exclusive. We have identified concomitant BRAF and RAS mutations in seven patients. DNA was extracted from formalin-fixed paraffin-embedded tumor tissue and the mutation status of the RAS gene (exons 2, 3, 4) and BRAF (exon 15 V600, V597) was assessed using a polymerase chain reaction enzyme-linked mini sequence assay-based DNA sequencing method. Three patients harbored Kirsten rat sarcoma viral oncogene homolog (KRAS) with a codon 13 mutation (gly13asp) along with a BRAF variation of L597V in exon 15 (p. leu597val, c.1789C>G (CTA>GTA). Two patients harbored KRAS with codon 12 mutations; one harbored the gly12val mutation with a variation of leu597val in the BRAF exon 15 codon, the other harbored a gly12asp mutation with p. leu597val, c.1789C>G (CTA>GTA) in the BRAF exon 15 codon. One patient harbored a codon 117 mutation with a BRAF V600E mutation. The last patient harbored a NRAS exon 2 (gly12asp) mutation with the GGT/GAT, V600G mutation in the BRAF exon 15 codon. Consequently, concomitant KRAS and BRAF mutations are very rare. Although it is known that the survival of concomitant RAS/BRAF mutation carriers is generally poor, we have shown that survival of concomitant RAS/BRAF mutation carriers is variable.



How to cite this article:
Ates O, Yalcin S. Concomitant RAS and BRAF mutation in colorectal cancer - A report of 7 cases.Indian J Cancer 2019;56:176-179


How to cite this URL:
Ates O, Yalcin S. Concomitant RAS and BRAF mutation in colorectal cancer - A report of 7 cases. Indian J Cancer [serial online] 2019 [cited 2019 Dec 7 ];56:176-179
Available from: http://www.indianjcancer.com/text.asp?2019/56/2/176/257558


Full Text



 Introduction



The prognosis of metastatic (m) colorectal carcinoma (CRC) is poor. The median overall survival (OS) has been extended up to 30 months with new targeted drugs. Target treatment has addressed two pathways, the antiepidermal growth factor receptor (EGFR) and vascular endothelial growth factor pathways. Vascular endotelial growth factor-A (VEGFA) is secreted by hypoxic tumor cells, especially in Kirsten rat sarcoma viral oncogene homolog (KRAS) mutant patients. Bevacizumab is a monoclonal antibody that blocks VEGFA in the plasma. The other targeted therapeutic agents are cetuximab and panitumumab, which are monoclonal antibodies against EGFR on tumor cells.[1] Ligand binding to the extracellular domain leads to allosteric activation via receptor dimerization and tyrosine kinase transphosphorylation, thus activating the RAS/MAPK pathway (RAS-RAF-MAPK) and the phosphor inositide 3-kinase (PI3K) pathway (PI3K-phosphatase and tensin homologue-Akt).[2] The antibodies which are active with wild-type KRAS in mCRC inhibit EGFR on the tumor cell with the intracellular downstream pathways of RAS-RAF-MAPK and blockage of PI3K-PTEN-AKT. But the benefit of EGFR blockade could recently not be shown for some KRAS wild-type mCRC patients.[3],[4] The reason may be the fact that there were mutations in BRAF, PI3K, and neuroblastoma RAS (NRAS).[2],[5] BRAF is a downstream molecule of EGFR and the prognosis of BRAF mutant mCRC is poor.[6],[7],[8],[9],[10],[11] The BRAF mutation in mCRC is seen in 5–10% of cases more commonly in proximal colon and in female patients;[12] it is known that the BRAF mutation is only seen in patients with RAS wild-type CRC.[10] BRAF and RAS are not mutually exclusive.

In the present case series, we evaluated the association of RAS and BRAF mutations with clinicopathological features in CRC patients in the Turkish population and their potential roles as prognostic biomarkers.

 Case Series



We reviewed a total of 600 samples tested in the clinical laboratory for RAS and BRAF mutations from 2009 to 2015. We elucidated concomitant KRAS and RAF mutations in seven patients (1%). We identified these cases randomly. Written consent was given by the patients for their information to use for research. Mutations were analyzed by pathologists experienced in gastrointestinal tumors. DNA was extracted from formalin-fixed paraffin-embedded tumor tissue and the mutation status of KRAS, NRAS (exons 2, 3, 4), and BRAF mutation (exon 15 V600, V597) was assessed using a polymerase chain reaction (PCR)-enzyme-linked mini sequence assay-based DNA sequencing method.[13] For detection of mutations, the protocol supplied by the manufacturer of PCR products was applied using the ABI PRISM SNaPshot Multiplex Kit (Applied Biosystems).

Median diagnosis age was 58 (52-61) years. Five of these patients were males. Three patients had right colon carcinoma, three patients had rectal carcinomas, and one patient had left colon carcinoma [Table 1]. All of the patients harbored concomitant RAS and BRAF mutations. The KRAS codon 13 mutation (gly13asp) was seen in three patients with BRAF variations in exon 15 (p. leu597val, c.1789C>G (CTA>GTA). Two patients had a KRAS mutation in codon 12, one of them harbored GGT/GTT, gly12val and the other patient harbored gly12asp mutation with a variation of in the BRAF exon 15 codon [Table 1]. The BRAF V600E mutation was seen only in the sixth patient, who harbored the KRAS codon 117 mutation. The last patient harbored a NRAS exon 2 (gly12asp) mutation with the GGT/GAT, V600G mutation in the BRAF exon 15 codon. Most of patients had metastasis, except for one patient (patient 2). The median OS was 47 months.{Table 1}

 Discussion



In the present study, we have identified seven cases who harbored concomitant RAS/BRAF mutations. Most of our patients (five of them) were operated. Median OS is 47 months.

Over the last few decades, research into CRC genomics and epigenetics has significantly advanced. Three distinct pathways abnormalities have been described for the development of CRC: chromosomal instability (CIN), microsatellite instability (MSI), and CIMP pathways.[14] CIN, which would be loss or gain of a whole chromosome, occurs as a result of cumulative mutations of oncogenes and tumor suppressor genes. The second model is MSI, which is seen only in 15% of CRC, causing mutations via DNA mismatch repair genes (MMR). Defective MMR can develop from inherited germline mutations in MMR genes (MLH1, MSH2, MSH6, PMS2) associated with Lynch syndrome. Half of patients with sporadic defective MMR carry a BRAF oncogene mutation. Proximal tumors, BRAF mutations, mucinous and poorly differentiated adenocarcinoma in female patients are prone to MSI,[15],[16],[17],[18] whereas distal tumors, which are more common in men than women, are characterized by loss of heterozygosity and mutation of TP53.

KRAS is an oncogene that encodes a protein with membrane bound GTP. KRAS mutations occur in exon 2 (codon 12 and 13), exon 3 (codon 59 and 61), and exon 4 (codon117, 146) in CRC and activate the MAPK pathway.[19],[20] KRAS mutations are seen in many parts of the colon at various rates (35–45%). In addition, other RAS mutations, NRAS exon 2-3-4 or KRAS exon 3-4, are seen in 10% of wild-type cases of KRAS exon 2. In a trial in the Turkish population, the KRAS mutation frequency was 35% and 30% in recto sigmoid and colon cancer, respectively.[21] In the TURKRAS study, a KRAS mutation was detected in 45% of cases.[22] There is a significantly higher KRAS mutation frequency in female patients compared to male patients. G12D and G12V mutations are the most common mutations, with rates of 28% and 25.9%, respectively. The most common KRAS mutation was the codon 12 (gly12Ala) mutation in that trial.[21] In our study, most patients harbored the codon 13 mutation (gly13asp). The codon 13 mutation is rare. In a far eastern study, where 676 patients were evaluated[16] KRAS codon 12 and 13 mutations were observed in 25.7 and 6.8% of cases, respectively. In another study evaluating 84 patients in total, mutations of KRAS codon 12 and 13 were found in 28.5% and 3% of cases, respectively.[21]

The BRAF gene is localized in 7q34 and consists of 18 exons. Usually, exon 15 and 11 mutations are observed. The BRAF mutation is more commonly seen in serrated and hyperplastic polyps, especially in proximal colon and in female patients.[12] The BRAF mutation in mCRC is seen in 5–10% of cases. It is known that the BRAF mutation is only seen in patients with RAS wild-type CRC.[10] BRAF and RAS are not mutually exclusive. The BRAF mutation is rarely seen in KRAS mutant CRC patients.[17],[19],[23],[24] Shen et al. determined the association of these mutations in 11 patients in their studies.[16] BRAF exon 15 and exon 11 mutations were seen in seven and four patients, respectively. In our study, patients had BRAF mutation at exon 15 [Table 1]. In another trial by Mao et al., the rate of KRAS, BRAF, and NRAS was 43%, 25%, and 8%, respectively.[17] They found that six patients harbored concomitant KRAS and BRAF mutations.

BRAF mutations are seen commonly in the right colon and rarely seen in the left colon and rectum (2%).[25] In our study, we defined concomitant KRAS and BRAF mutations, in which three patients had right colon cancer, three patients had left colon, and two had rectal cancer. The BRAF mutation is often seen in women and is associated with a poor prognosis. Patients with the BRAF V600 mutation usually respond poorly to standard therapy, with median PFS 2.5 months after second-line treatment and median survival of 12 months. The OS of patients with KRAS and BRAF mutations is generally poor.[26] But the survival of some patients was longer than in the literature in our study.

Consequently, concomitant KRAS and BRAF mutations are very rare. Although it is known that the survival of concomitant RAS/BRAF mutation carriers is generally poor, we have shown that survival of concomitant RAS/BRAF mutation carriers is variable.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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