Braf In Melanoma: Pathogenesis Diagnosis Inhibition And Resistance
Keith T. Flaherty
1Division of Hematology/Oncology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02114, USA
2Massachusetts General Hospital Cancer Center, Harvard Medical School, Boston, MA 02114, USA
Since the initial discovery that a subset of patients with cutaneous melanoma harbor BRAF mutations, substantial research has been focused on determining the pathologic consequences of BRAF mutations, optimizing diagnostic techniques to identify these mutations, and developing therapeutic interventions to inhibit the function of this target in mutation-bearing tumors. Recently, advances have been made which are revolutionizing the standard of care for patients with BRAF mutant melanoma. This paper provides an overview on the pathogenic ramifications of mutant BRAF signaling, the latest molecular testing methods to detect BRAF mutations, and the most recent clinical data of BRAF pathway inhibitors in patients with melanoma and BRAF mutations. Finally, emerging mechanisms of resistance to BRAF inhibitors and ways of overcoming this resistance are discussed.
2. RAF Signaling and Pathogenesis of Melanoma
4. Inhibitors of RAF Signaling
5. BRAF Inhibitors
5.2. Higher Potency BRAF Inhibitors
6. MEK Inhibitors
7. Emerging Mechanisms of Resistance to BRAF Inhibition
8. Future Directions
Determining Genetic Heterogeneity Of Melanoma
Data have shown that the molecular profile of a tumor changes over time due to various selection pressures., Tumor heterogeneity in advanced-stage melanoma has important implications for molecular testing and thus treatment. Shain et al. examined 37 primary melanocytic neoplasms and their adjacent precursor lesions, ultimately microdissecting and sequencing 150 distinct areas . Interestingly, tumors that lacked malignant behavior harbored only BRAF V600E mutations. The mutation load increased with progression, and unique patterns of genetic changes, termed evolutionary trajectories, for different melanoma subtypes were observed. Intermediate lesions were enriched for NRAS mutations and additional driver mutations. Progression was marked by the appearance of TERT promoter mutations and an increasing burden of NRAS mutations in intermediate lesions. This was followed by inactivation of CDKN2A or mutations in SWI/SNF chromatin remodeling genes in invasive melanomas and loss of PTEN and TP53 in advanced melanoma. In rare cases, lesions had both BRAF V600E and NRAS mutations identified. Although it is thought that BRAF and NRAS mutations are mutually exclusive, this study by Shain et al. and another recent study by Chiappetta et al. showed that these mutations can both be present, most likely due to clonal heterogeneity within the tumor.,
Genetic Testing For Braf Gene Mutation
Genetic testing of melanoma is generally performed when the cancer is at stage 2C, stage 3 or stage 4. Doctors perform a tumor biopsy to test for the mutation. During the biopsy, tissue is removed from the tumor either by cutting, scraping or aspirating .4 40-50% of all people with melanoma have the BRAF V600 mutation.3
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Braf Pv600e Mutation Testing In Malignant Melanoma
BRAF is a serine/threonine protein kinase, activating the MAP kinase/ERK-signalling pathway.
About 50% of melanomas harbour activating BRAF mutations .
Vemurafenib has been demonstrated to be effective in inhibiting melanomas carrying both the V600E and the rarer V600K mutation.
NICE recommends Vemurafenib as a possible treatment for unresectable or metastatic melanoma with the BRAF V600 mutation.
Molecular testing in Melanoma covering NRAS codons 12, 13 , 59 and 61 together with;BRAF V600 covering;cDNA positions; c.1798, c.1799 and c.1800 which account for >95% of all ;;BRAF mutations ” rel=”nofollow”>cancer.sanger.ac.uk/cancergenome/projects/cosmic/).
Cancers That May Have Braf Mutations
At the current time, several different types of cancer have been found to harbor BRAF mutations, though the frequency, as well as the response to BRAF inhibitors, varies.
BRAF mutations are an example of how cancer treatment is changing. In the past, cancers were usually treated according to type . BRAF inhibitors, in contrast, are what are now considered “tumor agnostic” medications. What this means is that the drugs may work for different types of cancer as long as the cancer cells have the same type of mutation responsible for driving the growth of the tumor.
Reading studies about BRAF mutations can be confusing. When the term “BRAF wild-type” or BRAF WT is used to describe a tumor, it refers to a cancer that does not have a BRAF mutation.
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Role Of Genetic Testing To Determine Melanoma Risk
There are no widely accepted guidelines for managing families with an increased hereditary risk for developing cutaneous melanoma.
The American Society of Clinical Oncology has stated that screening genetic tests for CDKN2A and CDK4 have not yet been shown to be of medical benefit.
GenoMEL has published consensus statements recommending against routine genetic testing for familial cutaneous melanoma except in rare circumstances.
The rationale for their recommendations is as follows:
- mutations have not yet been detected in the majority of families with hereditary cutaneous melanoma
- our understanding of melanoma risk to carriers of gene mutations is limited
- other factors appear to influence the risk
- negative testing may provide false reassurance.
GenoMEL recommends that:
- all high-risk family members are trained in skin self-examination
- have baseline skin examinations at age ten years by a physician specialist
- continue clinical skin examinations every six months by a physician specialist until melanocyticnaevi are stable
- have annual or biannual examinations after that time depending on numbers of atypical naevi regardless of CDKN2A mutation status.
The lack of definitive evidence showing clinical benefit from genetic testing further supports continued strict surveillance and optimised solar protection as primary goals for prevention of malignant melanoma.
Mutations Of The Braf Gene Are Related To Cancers
Although BRAF mutation and its connection to cancer was only identified in 2002, research done since then has pinpointed at least 30 different types of mutation that could be associated with cancers. The relationship between BRAF mutation and melanoma is particularly strong. The mutation doesnt play much of a role in other common cancers, such as lung cancer.
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Hereditary Vs Acquired Gene Mutations
It’s important to briefly discuss the difference between acquired gene mutations , and hereditary mutations, mutations that are inherited from one’s parents.
BRAF mutations associated with cancer are almost always acquired mutations. Unlike the BRCA mutations that have received a lot of attention in recent years, these mutations are not inherited from a person’s parents and cannot be passed down to children. They are present only in the cancer cells and not all of the cells in the body. Acquired mutations are much more common in oncology.
What Are The Chances A Mutated Gene Is Inherited
Every cell usually has two copies of each gene: one inherited from a person’s mother and one inherited from a person’s father.
Hereditary melanoma follows an autosomal dominant inheritance pattern, in which a mutation needs to happen in only one copy of the gene for the person to have an increased risk of getting the disease.
This means that a parent with a gene mutation may pass on a copy of the normal gene or a copy of the gene with a mutation. Therefore, a child who has a parent with a mutation has a 50% chance of inheriting that mutation. A brother, sister, or parent of a person who has a gene mutation also has a 50% chance of having the same mutation.
If a person has a first-degree relative with melanoma, his or her risk of developing melanoma is two to three times greater than the average risk. The risk is higher if several family members that live in different locations have been diagnosed with melanoma.
Most experts strongly recommend that people concerned about their family history of melanoma consult a genetic counsellor. Genetic counsellors are trained to assess the potential for hereditary cancer risk in a family and can identify appropriate genetic testing.
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Braf Gene Mutation Test For Melanoma
If the melanoma has spread to the lymph nodes, your doctor may test the melanoma cells for any change to the genes.
If you have melanoma that has spread to the lymph nodes, your doctor may test the melanoma cells for any change to the genes. Changes to the genes in our cells are called mutations. A mutation in the BRAF gene can cause the cells to make a protein. The protein encourages melanoma cells to divide and grow.
About half of people with melanoma have the BRAF gene mutation. If you have a BRAF gene mutation, your doctor may offer you a combination of targeted therapies. This treatment can help shrink or slow the growth of the melanoma. Targeted therapies are not helpful for people who do not have the BRAF mutation.
The tests can sometimes be done on the sample of melanoma cells that was removed when you had surgery. But sometimes, your doctor might want to take another sample of tissue to test. Your cancer doctor or specialist nurse can explain more about what tests you will have.
Treatment May Be Different For Those With Braf Mutations
If you have a mutation in your BRAF gene, melanoma cells will be making an altered form of protein that helps them grow. If thats the case, you’ll likely be treated with drugs that target this protein specifically. These meds are vemurafenib and dabrafenib . They’re designed to attack the BRAF protein directly, to reduce tumor size and slow its growth. Drugs that target the BRAF protein arent likely to work in patients whose melanomas have a normal BRAF gene.
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Braf Testing In People Without Cancer
As noted, BRAF mutations in people with cancer are almost always acquired BRAF mutations, but hereditary BRAF mutations may occur as well. In addition, BRAF mutations may also be associated with other noncancerous medical conditions. In other words, being told that you have a BRAF mutation if you have not been diagnosed with cancer does not mean that you have cancer .
Current And Developing Tests
Several BRAF mutation tests are currently in use; they are classified as DNA based or antibody based. DNA-based tests include those that use PCR to selectively amplify the mutant BRAF gene and others that directly determine the nucleotide sequence of the BRAF gene., Of note, PCR and other DNA-based tests reveal the presence of the gene but do not indicate whether the gene is being transcribed and translated into a protein.,
Currently, the only available antibody-based test for mutant BRAF protein uses the monoclonal antibody VE1 to detect expression in tumor samples using IHC., , This approach is effective in identifying a qualitative change but is less accurate in quantitating changes in expression than other antibody-based assays, such as the enzyme-linked immunosorbent assay.
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Are There Other Treatment Options For Braf
There are other types of targeted therapies that are used specifically in people with BRAF-positive melanoma. These therapies include BRAF inhibitors and MEK inhibitors. If you or your loved one has BRAF-positive melanoma, you may receive either, or both. People with wild-type melanoma do not receive BRAF or MEK inhibitors.;
Radiation, chemotherapy and surgery can also be used to treat melanoma.
Talk to your doctor about what plan they recommend based on your type, and stage, of melanoma. Be sure to get answers to all the questions you have.
When caught early, melanoma is highly treatable. Check your skin regularly using the Skin Self-Check tool.
Clinical Implications And Genetic Testing
First-line treatment of patients with BRAF V600 wild-type or mutation-positive, unresectable or metastatic melanoma is with nivolumab as a monotherapy or in combination with the immunotherapy ipilimumab.
ESMO included the following in its published guidelines for cutaneous melanoma :
- Mutation testing for actionable mutations is mandatory in patients with resectable or unresectable stage III or stage IV and is highly recommended in high-risk resected disease stage IIC, but not for stage I or stage IIAIIB.;BRAF;testing is mandatory. If the tumor is;BRAF;wild-type at the V600 locus , sequencing the loci of the other known minor;BRAF;mutations to confirm WT status and testing for;NRAS;and;c-kit;mutations is recommended.
- The current first-line standard of care treatments for unresectable stage III/IV are PD-1 blockade ; PD-1 blockade combined with CTLA-4 blockade ; and, in addition for;BRAF;V600-mutated melanoma, BRAF inhibition combined with MEK inhibition .
Dabrafenib and trametinib are;approved for use as monotherapy. Results from a clinical trial with the combination suggest that use of the 2 drugs together significantly improved progression-free survival, although the incidence of pyrexia was increased.
Flaherty KT, Infante JR, Daud A, Gonzalez R, Kefford RF, Sosman J, et al. Combined BRAF and MEK inhibition in melanoma with BRAF V600 mutations. N Engl J Med. 2012 Nov. 367:1694-703. . .
- Figure. The mitogen-activated protein kinase pathway.
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Targeted Therapy For Melanoma Skin Cancer
Some people with melanoma skin cancer have targeted therapy. It uses drugs to target specific molecules on cancer cells or inside them. These molecules help send signals that tell cells to grow or divide. By targeting these molecules, the drugs stop the growth and spread of cancer cells and limit harm to normal cells. Targeted therapy may also be called molecular targeted therapy.
You may have targeted therapy to:
- stop or control the growth and spread of cancer cells
- shrink a tumour
- relieve pain or control the symptoms of advanced melanoma skin cancer
Your healthcare team will consider your personal needs to plan the drugs, doses and schedules of targeted therapy. You may also receive other treatments.
A Braf Mutation Is Determined From A Biopsy
Genetic tests are usually performed using blood samples, although they might involve hair or skin. DNA can also be collected from a sample of cells, using a cheek swab. But the BRAF mutation cant be pinpointed with any of these methods. Instead, it has to be done on a melanoma tumor tissue sample, which means you would need a biopsy. Sometimes, a biopsy is already done to verify the diagnosis and determine staging, so its possible you wouldnt need a second biopsy for BRAF gene results.
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What Is Genetic Testing For Melanoma
Genes carry information in the form of DNA and control how cells function. ;A germlinemutation affects all the cells in the body. A somatic mutation is restricted to a tumour cell, such as a melanoma cell.
Germline genetic testing for melanoma provides information on whether the patient has a mutation predisposing him/her to develop melanoma.
- About 10% of melanomas are secondary to genemutations.
- The remaining 90% of melanomas are sporadic .
If the patient carries a germline gene mutation for melanoma, they may have an increased risk of developing a melanoma. They may have a positive family history for melanoma, and the onset of melanoma may be at a younger age compared to sporadic melanoma.
A biopsy sample of melanoma can be tested in the laboratory for somatic mutations to give information on treatment options or prognosis.
Braf May Play A Role In Other Cancers
Although its most associated with melanoma, the BRAF mutation may play a part in thyroid cancer, non-small cell lung cancer, and colorectal cancer. About 10 percent of colorectal cancer patients have a BRAF gene mutation, according to a report in Biomarkers in Cancer. Several clinical trials are ongoing to try and figure out the best treatment options for those with colorectal cancer who also have the BRAF mutation.
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What Somatic Genetic Testing Can Be Performed On The Melanoma Tumour
Oncogenic somatic mutations such as BRAF, NRAS, c-KIT or PTEN can be tested by immunohistochemistry or genomic techniques. Of these mutations, BRAF is the most common, observed in 5070% of cutaneous melanomas. Information about an oncogenic mutation may help the clinician choose the best treatment for advanced melanoma, as there are targeted therapies such as BRAF-inhibitors for tumours harbouring certain BRAF mutations. Oncogenic mutation testing is recommended in patients with metastatic disease or if there is potential for enrolment into a relevant clinical trial .
Somatic genetic testing on a tumour may also provide prognostic information. Prognostic tests are mostly still undergoing investigation.
- TERT promoter mutations can be assessed for diagnostic and prognostic information .
- Gene expression profiling , also known as the 31-gene prognostic test, consists of a panel of 31 genes . The GEP may be used to categorise melanoma into high-risk and low-risk tumours. High-risk patients are predicted to have a higher risk of distant melanoma metastases .
Tyr Tyrp1 And Asip Genes
Recently, other genes involved with skin pigment have been identified that may also increase susceptibility to inherited melanoma.
These genes encode the following proteins: TYR , TYRP1 , and ASIP .
Tyrosinase is a copper-containing enzyme that catalyses the production of melanin and other pigments and is encoded by the TYR gene.
TYRP1 is a protein involved in melanin production and is encoded by the TYRP1 gene.
Tyrp1 is involved in stabilising the tyrosinase enzyme and modulating its catalytic activity. Tyrp1 also affects melanocyte proliferation and melanocyte cell death.
Agouti signalling protein is a product of the Agouti gene, also called ASIP. ASIP affects the quality of hair pigmentation and act as an inhibitor of the -melanocyte stimulating hormone.
Mutations in TYR, TYRP1 or ASIP genes can result in the production of abnormal proteins and increase melanoma risk.
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How Braf Mutations Drive The Growth Of Cancer
The BRAF gene codes for a protein called B-Raf. Mutations in the BRAF gene are referred to as “activating mutations” as the mutation results in continuous production of the protein. The continued presence of the B-Raf proteins, in turn, results in continuous signaling for the cell to divide and grow.
B-Raf proteins are part of a signaling pathway that affects cell growth in several ways. This pathway:
- Promotes cell proliferation
- Promotes cell survival
- Aids in differentiation
- Aids in migration
- Inhibits apoptosis
This pathway is very important in the womb in the process of embryogenesis, but when continuously activated in an adult can result in uncontrolled growth of cells .
Part of the difficulty in treating cancer lies in the fact that cancer cells are not just a clone of cells that grows continuously, but they have other characteristics, such as the ability to break free and spread, avoid cell death, and more. They are also continuously changing, developing new mutations that may allow them to escape our current treatments.