Melanoma and BRAF

BRAF is a gene that makes a protein called B‐Raf. BRAF is involved in sending signals within cells that direct their growth. Identification of the BRAF V600 mutation and development of BRAF targeting drugs have radically changed clinical practice and outcomes of advanced or metastatic melanoma. Activating BRAF mutation has been estimated to occur in approximately 50% of cases of cutaneous melanoma. ^{[1, 2, 3, 4]}

Targeted therapies have shown significant benefit in the adjuvant setting, with a 53% decrease in the risk of relapse when compared with placebo. Such results led to FDA approval of BRAF plus MEK inhibitors for high-risk resected (stage III) melanoma patients. Assessment of BRAF mutations is considered a fundamental diagnostic procedure. ^{[4, 5, 6, 7]}

The European Society for Molecular Oncology (ESMO) included the following in its published guidelines for cutaneous melanoma ^[8] :

• 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 IIA–IIB.  BRAF testing is mandatory. If the tumor is  BRAF wild-type at the V600 locus (class I BRAF mutant), sequencing the loci of the other known minor  BRAF mutations (class II and class III BRAF mutant) to confirm WT status and testing for  NRAS and  c-kit mutations is recommended. ^[8]
• The current first-line standard of care treatments for unresectable stage III/IV are PD-1 blockade (nivolumab, pembrolizumab); PD-1 blockade (nivolumab) combined with CTLA-4 blockade (ipilimumab); and, in addition for  BRAF V600-mutated melanoma, BRAF inhibition (vemurafenib, dabrafenib, encorafenib) combined with MEK inhibition (cobimetinib, trametinib, binimetinib). ^[8]

In a Cochrane Database study, the combination of BRAF plus MEK inhibitors was found to be the best treatment option, followed by BRAF inhibitors and combination of anti‐CLA4 plus anti‐PD1 monoclonal antibodies, anti‐PD1 monoclonal antibodies, MEK inhibitors, anti‐CTAL4 monoclonal antibodies, biochemotherapy, and conventional chemotherapy. Ranking analysis results for toxicity suggested that anti‐PD1 monoclonal antibodies were associated with the best safety profile, followed by chemotherapy, BRAF inhibitors, biochemotherapy, the combination of BRAF plus MEK inhibitors, MEK inhibitors, anti‐CTLA4 monoclonal antibodies, and the combination of anti‐CTLA4 plus anti‐PD1 monoclonal antibodies. ^[3]

The US Food and Drug Administration (FDA) previously approved interleukin-2 and dacarbazine in this setting; in clinical trials, each had response rates of 10-20% and neither showed an overall survival benefit. ^{[9, 10]}  Ipilimumab, a fully humanized antibody that binds to cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) and sustains an immune attack on neoplastic cells, is approved by the FDA for use in the metastatic setting. Approval was based on a randomized study showing that ipilimumab improved survival from 6 months to 10 months as compared to an experimental vaccine. ^[11] This advance promised new effective treatment for what was once a treatment-refractory disease, and more research is underway to investigate other molecular pathways that may be targeted in an effort to produce further significant results.

The use of immune checkpoint inhibitors for the treatment of advanced melanoma has evolved beyond monotherapies to combination strategies. This combination approach results in response rates around 60% and superior progression-free survival compared with ipilimumab monotherapy (median 11.5 versus 2.9 months). ^[12]

One potential advance that showed great promise in the preclinical setting, and now in the clinical setting, is the targeting of the BRAF kinase in melanoma. Vemurafenib and dabrafenib are BRAF kinase inhibitors available in the United States. Trametinib, a mitogen-activated extracellular signal regulated kinase (MEK) inhibitor, is also approved by the FDA. Encorafenib, a BRAF inhibitor, and binimetinib, a MEK inhibitor, are approved for use in combination in patients with unresectable or metastatic melanoma with a BRAF V600E or V600K mutation. The combination of encorafenib plus binimetinib demonstrated improvements in both progression-free survival and overall survival as compared to vemurafenib in the phase 3 COLUMBUS study in patients with BRAF V600–mutated melanoma. The combination of encorafenib and binimetinib is generally well tolerated, with a distinct safety profile, and was associated with low levels of pyrexia and photosensitivity. ^{[13, 14, 15, 16, 17, 18, 19, 5, 6, 20]}

A study by Hecht et al indicated that patients with BRAF-mutated melanoma have better overall survival and experience less toxicity when vemurafenib treatment is interrupted during radiotherapy instead of administered concomitantly. For patients who underwent interrupted treatment, median overall survival from the start of radiotherapy and from the beginning of vemurafenib treatment was 10.1 and 13.1 months, respectively, compared with 6.6 and 10.9 months, respectively, for the group that received concomitant therapy. Moreover, there was a greater incidence of skin toxicity of grade 2 or higher (based on Common Terminology Criteria for Adverse Events [CTCAE]) in the concomitant patients than in the interrupted group. ^[2]

The mitogen-activated protein (MAP) kinase pathway is an important driver in melanoma and is made up of several potential targets providing therapeutic options. ^[21] In this pathway, the activation of RAS proteins stimulates the RAF kinases ARAF, BRAF, and RAF1. This process causes the phosphorylation of the MEK kinases, which phosphorylate the ERK kinases. Activated ERK regulates cyclin D1, which, in turn, regulates multiple cellular processes involved in cell division (see Figure).

Figure. The mitogen-activated protein (MAP) kinase pathway.

Approximately 40-60% of melanomas contain a mutation in the gene that encodes BRAF that leads to constitutive activation of downstream signaling in the MAP kinase pathway. In 80-90% of these cases, the activating mutation consists of the substitution of glutamic acid for valine at amino acid 600 (V600E). ^{[22, 23]} In a series of 197 patients, Long and colleagues showed that BRAF mutations were associated with features of high-risk melanoma, including truncal location, earlier age of onset, lack of chronic skin damage, and shortened survival, ^[24] suggesting the value of inhibiting mutated BRAF.

Robert and colleagues analyzed the long-term data from randomized trials of combination therapy with dabrafenib plus trametinib as first-line therapy in patients with unresectable or metastatic melanoma with a BRAF V600E or V600K mutation. Approximately one third of the patients experienced long-term benefits. Overall survival rates were 37% (95% CI, 33 to 42) at 4 years and 34% (95% CI, 30 to 38) at 5 years. ^[25]

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 ^[8] :

• 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 IIA–IIB.  BRAF testing is mandatory. If the tumor is  BRAF wild-type at the V600 locus (class I BRAF mutant), sequencing the loci of the other known minor  BRAF mutations (class II and class III BRAF mutant) to confirm WT status and testing for  NRAS and  c-kit mutations is recommended. ^[8]
• The current first-line standard of care treatments for unresectable stage III/IV are PD-1 blockade (nivolumab, pembrolizumab); PD-1 blockade (nivolumab) combined with CTLA-4 blockade (ipilimumab); and, in addition for  BRAF V600-mutated melanoma, BRAF inhibition (vemurafenib, dabrafenib, encorafenib) combined with MEK inhibition (cobimetinib, trametinib, binimetinib). ^[8]

FDA approval for nivolumab monotherapy was based on data from the randomized phase 3 CheckMate-066 trial, which compared nivolumab monotherapy with dacarbazine in the first-line treatment of 418 patients with advanced BRAF wild-type melanoma. In an interim analysis, nivolumab demonstrated superior overall survival, which was the primary outcome. The overall survival rate at 1 year was 72.9% (95% CI, 65.5 to 78.9) in the nivolumab group and 42.1% (95% CI, 33.0 to 50.9) in the dacarbazine group. A significant benefit with respect to overall survival was observed in the nivolumab group, as compared to the dacarbazine group (hazard ratio for death, 0.42; 99.79% CI, 0.25 to 0.73; P< 0.001). Median progression-free survival was also improved in the nivolumab-treated patients, compared to those who received dacarbazine (5.1 vs 2.2 months; HR, 0.43; P < 0.001). ^[26]

The FDA approved the combination regimen of nivolumab plus ipilimumab in previously untreated patients with BRAF V600 wild-type unresectable or metastatic melanoma. Approval was based on results from the phase 2 CheckMate-069 study. Of the 142 patients enrolled, 109 had both BRAF wild-type and BRAF mutation-positive melanoma. The primary endpoint was objective response rate (ORR). In patients with BRAF wild-type melanoma treated with the combination regimen, the overall response rate was 61% (95% CI: 48-71) compared to 11% (95% CI: 3-25) in patients given ipilimumab monotherapy (P< 0.001). Additional analysis showed that complete response was seen in 22% of patients. Partial responses were seen in 43% of the combination group and in 11% of the ipilimumab monotherapy group. The combination group had a 60% reduction in the risk of progression compared to those given ipilimumab alone (HR=0.40; 95% CI: 0.22-0.71; P< 0.002). Median PFS was 8.9 months with the combination (95% CI: 7.0, NA) and 4.7 months with ipilimumab alone (95% CI: 2.8-5.3). ^[27]  This indication was later expanded to include mutation-positive melanoma, making nivolumab effective across BRAF status. ^[28]

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. ^{[29, 30]}

The FDA approved trametinib for use in combination with dabrafenib for treating patients with unresectable or metastatic melanoma with BRAF V600E or V600K mutations. Approval was based on the demonstration of response rate and median duration of response in a phase I/II study. ^[1]

Data from the phase 3 trial of vemurafenib indicated that the drug has a rapid onset of response but a short duration of response; thus, the drug might be best suited for patients with rapidly progressing and/or symptomatic disease. By contrast, patients with asymptomatic and/or slowly progressing disease could be considered first for ipilimumab in an attempt to elicit an immune response and then be switched to vemurafenib upon signs of progression. ^[31]  If one were to follow this approach, patients with localized disease who are considered at “high risk” for metastasis should be tested for BRAF mutations so that the information would be available if there is a need to initiate vemurafenib immediately. The definition of “high risk” in this setting is variable and could include patients with stage IIB disease or higher, signs of ulceration, positive lymph nodes, larger tumors, etc.

For patients with newly diagnosed, rapidly progressing metastatic melanoma, a BRAF mutation analysis should be done immediately. The cobas 4800 BRAF V600 Mutation Test detects the mutation in formalin-fixed, paraffin-embedded tissue. Although the manufacturer states that the test can be performed in fewer than 8 hours from receipt of the specimen, physicians in private practice who do not routinely process specimens for genetic testing might find that waiting for a positive or negative test result might constitute an unacceptable delay in treatment initiation. It would be considered off-label use to start treatment immediately while waiting for test results and then discontinuing if the test results show that a mutation is not present. Whether this practice will nevertheless gain traction in the community remains to be seen.

The American Academy of Dermatolory has recommended that for the first 3 months of BRAF inhibitor monotherapy, patients with numerous squamoproliferative neoplasms should undergo dermatologic evaluation every 2-4 weeks, although less skin toxicity is associated with the standard treatment, combination BRAF/MEK inhibition. ^[32]