SEARCH

SEARCH BY CITATION

Keywords:

  • BRAF;
  • NRAS;
  • prognostic factor;
  • melanoma;
  • stage IV;
  • clinical features

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. FUNDING SUPPORT
  8. CONFLICT OF INTEREST DISCLOSURES
  9. REFERENCES

BACKGROUND

Hotspot mutations in BRAF and NRAS are the most common somatic events in patients with melanoma. These mutations occur at highly conserved residues, but include several different substitutions. To determine whether specific mutations are clinically important to differentiate, tumor characteristics and clinical outcomes were compared among patients with advanced melanoma with 1) BRAF V600E versus V600K mutations and 2) NRAS exon 1 versus exon 2 mutations.

METHODS

Retrospective clinical and pathologic data were collected for patients with advanced melanoma with BRAF or NRAS mutations. The demographics, tumor characteristics, and clinical outcomes of the patients were compared to identify significant mutation-specific associations.

RESULTS

Among 302 patients with activating BRAF mutations, 76% had BRAF V600E and 24% had V600K substitutions. Compared with V600E, the presence of a V600K mutation was significantly associated with older age (median, 60.0 years vs 44.7 years; P < .001), male sex (80% vs 59%; P = .001), head/neck primary tumor location (30% vs 15%; P = .0026), shorter interval to stage IV disease (0.98 years vs 2.8 years; P = .015), and a shorter overall survival from the time of diagnosis of stage IV disease (median, 2.44 years vs 1.25 years; hazards ratio, 1.68 [P = .014]). Comparison of 136 patients with NRAS exon 1 (18%) and exon 2 (82%) mutations found an association with primary tumor histology (P = .0096) only.

CONCLUSIONS

The presence of different substitutions at BRAF V600 correlates with patient demographics, tumor characteristics, and prognosis. These findings demonstrate the presence of mutation-specific clinical differences between different BRAF genotypes in patients with melanoma, and support the incorporation of this information in patient evaluation and clinical trial design. Cancer 2013;119:3821–3829. © 2013 American Cancer Society.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. FUNDING SUPPORT
  8. CONFLICT OF INTEREST DISCLOSURES
  9. REFERENCES

In 2013, an estimated 76,790 patients will be diagnosed with, and 9480 patients will die of, melanoma.[1] The clinical management of patients with melanoma is evolving rapidly due to improved understanding of the molecular drivers and heterogeneity of this disease.[2-7] BRAF mutations are detected in approximately 50% of patients with cutaneous melanomas and approximately 95% of these mutations result in substitutions for the valine at residue 600 (V600).[2] The most common mutation results in substitution of glutamic acid (V600E), which increases the catalytic activity of the BRAF protein > 100-fold, causes constitutive activation of the RAS-RAF-MEK-MAPK pathway, and promotes uncontrolled proliferation.[8] Other mutations result in substitution of other amino acids at the V600 site, most frequently lysine (V600K), but also aspartic acid (V600D) and arginine (V600R), all of which increase the catalytic activity of BRAF.[9] The RAF-MEK-MAPK pathway may also be activated in melanoma by point mutations in the neuroblastoma RAS viral (NRAS) oncogene. NRAS mutations are found in approximately 15% to 25% of melanomas, the majority occurring in exon 1 (codons 12 and 13) and exon 2 (codon 61).[2] BRAF V600 mutations and NRAS mutations are essentially mutually exclusive in patients with treatment-naive melanoma.[10]

The development of selective small-molecule inhibitors of V600-mutant BRAF proteins, such as vemurafenib and dabrafenib, has markedly changed the therapeutic options for patients with metastatic melanoma. Phase 1 testing of both agents demonstrated significant clinical benefit in patients with metastatic melanoma with V600 BRAF mutations, but not in patients without these mutations.[5, 11] In the BRIM3 trial, patients with metastatic melanoma with BRAF V600E mutations who were treated with vemurafenib had significant improvements in overall response rate, progression-free survival (PFS), and overall survival (OS) compared with those receiving dacarbazine.[7] Dabrafenib also improved clinical responses and PFS compared with chemotherapy in a randomized phase 3 trial of patients with BRAF V600E mutations.[12] Although the initial clinical trials of vemurafenib only included patients with BRAF V600E mutations, testing of dabrafenib also included patients with BRAF V600K mutations. It is interesting to note that the observed overall response rate appears to be lower and PFS appears to be shorter in patients with V600K mutations compared with patients with V600E mutations, despite dabrafenib binding to both proteins equally.[11, 13]

In addition to being predictive markers for specific therapies, oncogenic mutations may be prognostic. Several studies have identified clinical associations with the presence of any activating BRAF and NRAS mutation in patients with melanoma. To the best of our knowledge, few studies to date have examined the clinical or pathological differences between patients with BRAF V600E and V600K mutations,[14] and no studies have compared the associations of NRAS exon 1 and exon 2 mutations. The identification of mutation-specific associations may improve risk assessment in patients, as well as have implications for patient management and clinical trials. We previously identified a cohort of 677 patients with advanced melanoma who were treated at The University of Texas MD Anderson Cancer Center (MDACC) with Clinical Laboratory Improvement Amendments-certified BRAF and NRAS mutation testing results.[15] Our comparison of all patients with BRAF mutations, all patients with NRAS mutations, and patients with wild-type BRAF and NRAS (“wild-type”) identified several significant associations, including age at diagnosis, sites of metastasis at the time of diagnosis of stage IV disease, and OS after the diagnosis of stage IV disease.[15] To further our understanding of the clinical significance and heterogeneity of melanoma, and to identify possible sources for the differences in outcomes observed among patients with activating BRAF mutations with BRAF inhibitors, we report herein a comparative analysis of melanoma patients with 1) V600E and V600K BRAF mutations and 2) exon 1 and exon 2 NRAS mutations.

MATERIALS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. FUNDING SUPPORT
  8. CONFLICT OF INTEREST DISCLOSURES
  9. REFERENCES

Patient Selection and Clinical Data Collection

The analysis was performed on the cohort of patients previous described by Jakob et al.[15] Briefly, under an Institutional Review Board-approved protocol, the molecular testing results for patients with melanoma with evaluable, Clinical Laboratory Improvement Amendments-certified testing for both BRAF and NRAS mutations performed by the Molecular Diagnostics Laboratory at MDACC from February 1, 2007 to September 13, 2010 were reviewed. Clinical, pathological, and demographic data were collected for all patients.[15] Treatment with the selective BRAF inhibitors vemurafenib (Roche, Indianapolis, IN) or dabrafenib (GlaxoSmithKline, Parsippany, NJ), or with the MEK inhibitors selumetinib (AstraZeneca, Willington, Del) or trametinib (GlaxoSmithKline), was also recorded.

Mutation Testing

Mutation testing was performed by pyrosequencing of BRAF exon 15 (inclusive of codons 595-601) and NRAS exon 1 (codons 12 and 13) and exon 2 (codons 60 and 61) as previously described.[15]

Statistical Analysis

The Fisher exact test was used to assess the association between categorical variables and mutational status. The Kaplan-Meier method was used to estimate the distribution of OS, and distributions were compared using the log-rank test. Cox proportional hazards regression models were fit to assess the association between multiple variables and OS. P values < .05 were considered to be statistically significant. No statistical adjustment was made for the multiplicity of testing. Statistical analyses were performed in R statistical software (version 2.15.1; R Foundation, Vienna, Austria [r-project.org]).

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. FUNDING SUPPORT
  8. CONFLICT OF INTEREST DISCLOSURES
  9. REFERENCES

BRAF V600E Versus V600K: Patient Demographics and Primary Tumor Characteristics

The cohort of 302 patients with activating BRAF mutations included 230 patients (76%) with a V600E mutation and 72 patients (24%) with a V600K mutation. Demographics and primary tumor characteristics are presented in Table 1. Patients with a V600E mutation were younger at the time of diagnosis (median age, 44.7 years vs 60.0 years; P < .0001). Sex was also found to be significantly (P = .001) associated with mutational type. Among the 108 female patients with activating BRAF mutations, 87% had a V600E mutation, and only 13% had a V600K mutation. Among men (n = 194), 70% had a V600E mutation and 30% had a V600K mutation.

Table 1. Demographics and Primary Tumor Characteristics of Patients With BRAF Mutations
CharacteristicsAll Patients No.V600E No. (%)V600K No. (%)P
  1. Abbreviations: ENT, ear, nose, and throat; GU, genitourinary.

No. of patients30223072
Median age, y49.744.760.0<.0001
Sex    
Male194136 (70)58 (30).001
Female10894 (87)14 (13) 
Primary melanoma type    
Cutaneous245186 (76)59 (24)1.00
Soft parts11 (100)0 (0) 
Mucosal11 (100)0 (0) 
Unknown5542 (76)13 (24) 
Location    
Trunk9983 (84)16 (16).0026
Arm/leg/foot8569 (81)16 (19) 
Head/neck/scalp6135 (57)26 (43) 
ENT/GU/anorectal11 (100)0 (0) 
Unknown5642 (75)14 (25) 
Primary tumor histology    
Mucosal/acral lentiginous, lentigo maligna117 (64)4 (36).24
Nodular, superficial spreading136109 (80)27 (20) 
Other54 (80)1 (20) 
Unknown150110 (73)40 (27) 
Mean Breslow thickness2.32.22.5.38
Cutaneous tumors: mitotic rate, mm2    
≤12720 (74)7 (26).80
>112193 (77)28 (23) 
Not stated9773 (75)24 (25) 
Cutaneous tumors: ulceration    
Yes6854 (79)14 (21).46
No9369 (74)24 (26) 
Not stated8463 (75)21 (25) 

The majority (81%) of patients with a BRAF mutation had a primary cutaneous melanoma. There was no association noted between the specific BRAF mutation and primary melanoma type (P = 1.00). A significant difference in primary cutaneous tumor location was identified (P = .003). For patients with a V600E mutation, the most common primary tumor sites were the trunk (36%) and extremities (30%), whereas tumors on the head/neck were relatively uncommon (15%). In contrast, the most common tumor location for patients with a V600K mutation was the head/neck (36%). There was no significant difference noted between the 2 mutation subgroups with regard to primary tumor histology, Breslow thickness, mitotic rate, or ulceration.

BRAF V600E Versus V600K: Stage IV Disease and Outcomes

Among the 302 patients with BRAF-mutant melanoma, 241 developed stage IV disease (178 patients with the V600E mutation and 63 patients with the V600K mutation) (Table 2). Patients with a V600E mutation were significantly younger at the time of diagnosis of stage IV disease (median age, 49.0 years vs 63.8 years; P < .0001). Patients with a V600K mutation had a shorter interval between the initial melanoma diagnosis and the diagnosis of stage IV disease compared with patients with the V600E mutation (median, 0.98 years vs 2.8 years; P = .015). Analysis of the sites of involvement at the time of diagnosis of stage IV disease demonstrated no significant association between BRAF mutation status and involvement of specific metastatic sites. There was also no difference noted with regard to in M classification at the time of diagnosis of stage IV disease between the patients with BRAF V600E and those with V600K mutations (215 patients with known lactate dehydrogenase [LDH] [P = .45] and 241 patients with unknown LDH [P = .25] levels)

Table 2. Demographics and Clinical Characteristics at Time of Diagnosis of Stage IV Disease for Patients With BRAF Mutations
CharacteristicsAll BRAF No.V600E No. (%)V600K No. (%)P
  1. Abbreviations: LDH, lactate dehydrogenase; LMD, leptomeningeal; ULN, upper limit of normal; WNL, within normal limits.

No. of patients24117863
Median age, y54.249.063.8.0001
Time to diagnosis, y2.262.80.98.015
LDH    
>ULN5637 (66)19 (34).14
WNL11387 (77)26 (23) 
Not stated725418 
Skin/subcutaneous metastasis    
Yes7254 (75)18 (25) 
No168124 (74)44 (26).87
Not stated101 
Lymph node metastasis    
Yes10676 (72)30 (28).56
No134101 (75)33 (25) 
Not stated101 
Lung metastasis    
Yes13198 (75)33 (25).77
No10979 (72)30 (28) 
Not stated110 
Brain/LMD metastasis    
Yes5538 (69)17 (31).38
No184139 (76)45 (24) 
Not stated211 
Liver metastasis    
Yes5134 (67)17 (33).21
No187142 (76)45 (24) 
Not stated321 
Bone metastasis    
Yes4834 (71)14 (29).58
No190142 (75)48 (25) 
Not stated321 
Soft tissue metastases    
Yes4939 (80)10 (20).37
No190138 (73)52 (27) 
Not stated211 
Other visceral metastases    
Yes5236 (69)16 (31) 
No186139 (75)47 (25).48
Not stated330 
M1 category without LDH    
A3328 (85)5 (15).25
B5038 (76)12 (24) 
C158112 (71)46 (29) 
Not stated000 
M1 category with LDH    
A1412 (86)2 (14).45
B3225 (78)7 (22) 
C169120 (71)49 (29) 
Not stated26215 

Analysis of OS for all patients with a BRAF mutation from the time of diagnosis of stage IV disease identified a significant difference between patients with the BRAF V600E mutation compared with those with the V600K mutation (Fig. 1A). Patients with the V600E mutation had longer OS from the time of diagnosis of stage IV disease (n = 178 patients; median, 2.44 years) compared with patients with the V600K mutation (n = 63 patients; 1.25 years) (hazards ratio [HR], 1.68; P = .014). Because this cohort of patients was diagnosed with stage IV disease before targeted therapies received regulatory approval for melanoma, relatively few patients (n = 73 patients) were treated with selective BRAF or MEK inhibitors.[5-7, 11, 12, 16-20] Among the few patients who did receive such agents, the median OS from the time of diagnosis of stage IV disease was not reached for patients with the V600E mutation (n = 59 patients) and was 2.21 years for those with the V600K mutation (n = 14 patients) (P = .15) (Fig. 1B). Among the patients with stage IV disease who did not receive a BRAF or MEK inhibitor, there was a strong but nonsignificant trend toward shorter OS for those with the V600K mutation (49 patients; 10.4 months) compared with patients with the V600E mutation (119 patients; median, 14.9 months) (P = .084) (Fig. 1C). Because this cohort of patients included individuals who had been diagnosed with stage IV disease at a significant interval before the implementation of routine mutation analysis, an analysis of patients who underwent BRAF testing within 6 months of diagnosis was also performed to reflect current clinical practice/populations. Analysis of these patients similarly indicated that the median OS from the time of diagnosis of stage IV disease for patients with a V600K mutation (40 patients; median, 0.67 years) was significantly shorter than that for patients with a V600E mutation (108 patients; median, 1.19 years) (P = .02).

image

Figure 1. Overall survival from the time of diagnosis of stage IV melanoma is shown. (A) All patients with a BRAF V600E (solid line) or V600K (dashed line) mutation are shown. (B) Patients with a BRAF V600E or V600K mutation who received treatment with a BRAF or MEK inhibitor are shown. (C) Patients with a BRAF V600E or V600K mutation who were not treated with a BRAF or MEK inhibitor are shown. (D) All patients with an NRAS exon 2 (solid line) or exon 1 (dashed line) mutation are shown.

Download figure to PowerPoint

Multivariate analysis of OS from the time of diagnosis of stage IV disease incorporating specific BRAF mutation status, serum LDH, anatomical M category, age, sex, and treatment with a selective BRAF or MEK inhibitor was performed for patients for whom data regarding all variables were available (169 patients) (Table 3). The validated prognostic factors of higher stage (M1b: P = .007; M1c: P = .009) and elevated LDH (P < .0001) were found to be significantly associated with shorter OS, as was male sex (HR, 1.94; P = .02). Treatment with a selective inhibitor was associated with improved OS (P < .0001), which is consistent with the results of randomized studies. The presence of a V600K mutation (HR, 1.95; P = .02) was also found to be significantly associated with shorter OS.

Table 3. Multivariate Analysis of OS in Patients With Stage IV Disease With BRAF Mutations
VariableNo. of PatientsMedian OS, YearsHR95% CIP
  1. Abbreviations: 95% CI, 95% confidence interval; HR, hazards ratio; LDH, lactate dehydrogenase; OS, overall survival.

Mutation status     
V600E1242.44
V600K451.251.951.10–3.47.02
Stage     
M1a20Not reached
M1b372.444.761.53–14.76.007
M1c1121.304.011.42–11.31.009
LDH     
Normal113Not reached
Elevated560.863.662.21–6.05<.0001
Selective inhibitor use     
No111Not reached
Yes581.230.310.18–0.55<.0001
Age169 0.980.97–1.00.06
Sex     
Female542.44
Male1151.331.941.10–3.42.02

NRAS Exon 1 Versus Exon 2 Mutations: Patient Demographics and Primary Tumor Characteristics

Among the 136 patients with melanoma with an activating NRAS mutation, 24 (18%) had a mutation in exon 1 and 112 (82%) had a mutation in exon 2 (Table 4). The median age at the time of diagnosis for patients with an exon 1 mutation was 56.2 years and was 55.7 years for those with an exon 2 mutation (P = .70). There was no significant association noted between mutation type and sex (P = 1.00). There was an association noted between the specific NRAS mutations and melanoma subtype (P = .048). Exon 1 mutations were relatively rare among patients with cutaneous primary tumors (19 of 109 patients; 17%) and those with unknown primary tumors (2 of 22 patients; 9%), but were more common in individuals with mucosal melanomas (3 of 5 patients; 60%). There was also a significant difference noted in primary tumor histology (P = .0096). Although the prevalence of exon 1 and exon 2 NRAS mutations was equivalent in the group of patients with acral or mucosal melanomas, the prevalence of exon 2 mutations was much higher (86% vs 14%) in the group of patients with combined nodular and superficial spreading melanomas, as well as in those with “other” histologies. There was no significant association noted with cutaneous primary tumor location, Breslow thickness, mitotic rate, or ulceration by specific NRAS mutation.

Table 4. Demographics and Primary Tumor Characteristics of Patients With NRAS Mutations
CharacteristicsNRAS, All No.Exon 1 No. (%)Exon 2 No. (%)P
  1. Abbreviations: ENT, ear, nose, and throat; GU, genitourinary.

No. of patients13624112
Median age, y55.756.255.7.70
Sex    
Male8715 (17)72 (83)1.00
Female499 (18)40 (82) 
Primary type    
Cutaneous10919 (17)90 (83).048
Soft parts000 
Mucosal53 (60)2 (40) 
Unknown222 (9)20 (91) 
Location    
Trunk263 (12)23 (88).086
Arm/leg/foot5812 (21)46 (79) 
Head/neck/scalp254 (16)21 (84) 
ENT/GU/anorectal53 (60)2 (40) 
Unknown212 (10)19 (90) 
Primary tumor histology    
Mucosal/acral lentiginous. lentigo maligna147 (50)7 (50).0096
Nodular, superficial spreading588 (14)50 (86) 
Other649 (14)55 (86) 
Median Breslow thickness2.42.32.5.66
Cutaneous tumors, mitotic rate, mm2    
≤172 (29)5 (71).30
>16011 (18)49 (82) 
Not stated426 (14)36 (86) 
Cutaneous tumors, ulceration    
Yes338 (24)25 (76).30
No448 (18)36 (82) 
Not stated323 (9)29 (91) 

NRAS Exon 1 Versus Exon 2: Stage IV Disease and Outcomes

There was no significant difference noted with regard to the age of patients with NRAS exon 1 (17 patients; median age, 60.8 years) and exon 2 (87 patients; median age, 58.3 years) (P = .85) mutations at the time of a diagnosis of stage IV disease, or in the interval from the time of a primary melanoma diagnosis to a stage IV diagnosis (2.2 years vs 1.6 years; P = .86). There was no significant difference noted at the time of diagnosis of stage IV disease with regard to the prevalence of an LDH level greater than the upper limits of normal (P = .17), nor in the pattern/sites of metastatic involvement. There was also no difference in M classification at the time of diagnosis of stage IV disease between patients with NRAS exon 1 and exon 2 mutations in those with (P = .21) or without (P = .57) known serum LDH levels (Table 5).

Table 5. Demographics and Clinical Characteristics at the Time of Diagnosis of Stage IV Disease for Patients With NRAS Mutations
CharacteristicsNRAS, All No.Exon 1 No. (%)Exon 2 No. (%)P
  1. Abbreviations: LDH, lactate dehydrogenase; LMD, leptomeningeal; ULN, upper limit of normal; WNL, within normal limits.

No. of patients1041787
Median age, y59.060.858.30.85
Time to diagnosis, y3.94.23.90.86
LDH    
>ULN161 (6)15 (94).17
WNL5914 (24)45 (76) 
Not stated29227 
Skin/subcutaneous metastasis   .78
Yes336 (18)27 (82) 
No6911 (16)58 (84) 
Not stated20 (0)2 (100) 
Lymph node metastasis    
Yes457 (16)38 (84)1.00
No5710 (18)47 (82) 
Not stated202 
Lung metastasis    
Yes599 (15)50 (85).79
No438 (19)35 (21) 
Not stated202 
Brain/LMD metastasis    
Yes233 (13)20 (87).76
No8114 (17)67 (83) 
Not stated000 
Liver metastasis    
Yes202 (10)18 (90).51
No8215 (18)67 (82) 
Not stated202 
Bone metastasis    
Yes152 (13)13 (87)1.00
No8715 (17)72 (83) 
Not stated202 
Soft tissue metastases    
Yes162 (13)14 (87)1.00
No8615 (17)71 (83) 
Not stated202 
Other visceral metastases    
Yes246 (25)18 (75).20
No7710 (13)67 (87) 
Not stated312 
M1 category without LDH    
A113 (27)8 (73).57
B315 (16)26 (84) 
C629 (15)53 (85) 
Not stated000 
M1 category with LDH    
A62 (33)4 (67).21
B225 (23)17 (77) 
C659 (14)56 (86) 
Not stated11110 

There was no evidence of an association between OS after the diagnosis of stage IV disease and the types of NRAS mutation. Patients with an NRAS exon 1 mutation had a median OS of 1.1 years, whereas patients with exon 2 mutations had a median OS of 1.3 years (P = .95) (Fig. 1D).

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. FUNDING SUPPORT
  8. CONFLICT OF INTEREST DISCLOSURES
  9. REFERENCES

Although much attention has been focused on annotating which genes are mutated in cancer, several recent reports have suggested that different substitutions in a given oncogene may have specific clinical associations and/or functions.[14, 19, 21] The findings in the current study that several patient and tumor characteristics were significantly associated with specific BRAF and NRAS mutations add to this growing body of evidence, as well as to our understanding of the molecular complexity of melanoma.

The discovery of recurrent activating BRAF mutations in approximately 50% of cutaneous melanomas was a sentinel event in this disease.[8] Certified testing for BRAF mutations is now the standard of care for patients with stage IV melanoma due to the approval of vemurafenib. Although vemurafenib and the structurally unrelated selective BRAF inhibitor dabrafenib have demonstrated significant clinical benefit in patients with stage IV melanoma with activating BRAF mutations, there is also tremendous heterogeneity in both the degree of tumor shrinkage achieved and the duration of tumor response.[7, 12] The development of tests that can identify those patients who are likely to respond to these agents will help to guide appropriate clinical management as well as facilitate appropriate patient selection and design for future clinical trials. In a recent phase 1 clinical trial of dabrafenib in patients with metastatic melanoma, patients with a V600E mutation had a 56% confirmed response rate, in contrast to only 22% in patients with a V600K mutation.[11] More recently, dabrafenib was studied in patients with brain metastases with BRAF V600E or V600K mutations. In patients who had not received any previous central nervous system-directed therapies, the intracranial response rate was 39.2% (95% confidence interval, 28.0-51.2) for patients with V600E mutations and 6.7% for those with V600K mutations (95% confidence interval, 0.2-31.9).[13] Because the inferior outcomes in patients with V600K mutations were not predicted by preclinical testing, it is important to determine whether other clinical differences are associated with these mutations that may contribute to these observations.

Our analysis of patients with BRAF V600E and V600K mutations identified significant differences in sex, age, primary tumor location, interval from the time of initial melanoma diagnosis to diagnosis of stage IV disease, and OS after the diagnosis of stage IV disease. Because this cohort of patients underwent clinically indicated testing, which generally was performed in patients with stage IV disease, it is unknown whether the associations observed herein would also be detected in larger cohorts of patients with early-stage disease who do not develop metastatic disease.[20, 22] Our findings are similar to a recent analysis of an independent cohort of 143 Australian patients with melanoma with activating BRAF mutations. That study, which included 105 patients with V600E mutations, 27 with V600K mutations, and 11 patients with other V600 mutations, reported that V600K mutations were associated with increased age, primary tumor location on the head/neck, a higher degree of chronic sun damage (CSD), and shorter disease-free interval from the time of the primary melanoma diagnosis.[14] Although the current study did not specifically include an examination of the primary tumors for CSD, we did find that patients with V600K mutations were more likely to have a head/neck primary tumor location, which is associated with this histologic phenotype. The combined results of the current study and the Australian study support the rationale for a multiinstitutional study currently underway in which a similar analysis of patients with earlier stages of disease is being performed (unpublished data).

The results of both the MDACC and Australian studies suggest that BRAF V600K-mutant melanomas that give rise to metastases have a more aggressive clinical phenotype than tumors with the V600E mutation. Despite no significant difference noted between tumors with V600E and V600K mutations with regard to primary tumor Breslow thickness or ulceration, there was a markedly shorter interval from the time of initial melanoma diagnosis to the diagnosis of stage IV disease for patients with the BRAF V600K mutation versus those with the V600E mutation in our cohort. The Australian study also detected a significantly shorter metastasis-free survival for patients with the V600K mutation that was significant on multivariate analysis and that included age, sex, and primary tumor histologic type. We also observed a significantly shorter OS from the time of stage IV diagnosis for all patients with BRAF V600K mutations versus those with V600E mutations (P = .01) and a strong trend for shorter OS (P = .08), specifically among patients who were not treated with selective BRAF or MEK inhibitors.

Although BRAF inhibitors are likely to improve outcomes in patients with BRAF V600K mutations, a strong trend (P = .15) for shorter OS among patients with the V600K mutation who are treated with BRAF or MEK inhibitors versus those with V600E mutations was observed. The observations from clinical trials with dabrafenib are also consistent, with worse outcomes noted in patients with the V600K mutation.[11-13] Because CSD has been associated in recent whole-genome sequencing studies with extremely high rates of somatic mutations, it is possible the V600K mutations may be arising in the setting of widespread genetic alterations.[23] Deconvoluting this genetic landscape to identify coexisting mutations that may cause the inferior responses to selective BRAF inhibitors will require analysis of much larger cohorts of patients who have received this treatment. Additional analyses should also be undertaken to determine whether inferior outcomes are also observed with other therapies. These findings also support the importance of using BRAF mutation testing methodologies that allow for the detection and identification of substitutions other than V600E.[24]

We also compared the characteristics and outcomes of patients with NRAS exon 1 and exon 2 mutations. To our knowledge, this represents the first such comparative analysis of these molecularly defined subgroups of patients with melanoma. In contrast to the analysis of BRAF V600 mutations, there was no significant association observed with any of the patient characteristics or clinical outcomes. Recently, data from other tumor types that are characterized by mutations of other RAS isoforms have identified significant differences in signaling effects and clinical outcomes associated with the different amino acid substitutions that occur at the hotspots in mutant RAS genes.[21] Analysis of clinical associations associated with the 3 most common substitutions in exon 2 in this cohort of patients (Q61R, Q61K, and Q61L) failed to identify any significant substitution-specific differences (data not shown). However, this exploratory analysis was limited by the relatively small number of patients with NRAS in this cohort, and should not be considered definitive. The comparatively lower prevalence of melanoma in the general population, and of NRAS mutations within patients with this disease, will likely require multiinstitutional efforts to adequately determine whether such differences also exist in patients with melanoma. Such collaborative efforts will also be necessary to reach meaningful conclusions about clinical associations with other mutations in the BRAF gene.

The current study data support the need for continued analysis of clinical associations and outcomes associated with somatic mutations in melanoma. With the recent publication of 2 large whole-exome mutation analyses of melanomas and the imminent release of the initial results of The Cancer Genome Atlas melanoma effort, the molecular dictionary of this disease will be exponentially more complicated in the near future.[3, 4, 23] Although these molecular data may provide important information, the ultimate challenge will be to understand if and/or how it may be applied clinically to improve outcomes for patients with this highly aggressive disease.

FUNDING SUPPORT

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. FUNDING SUPPORT
  8. CONFLICT OF INTEREST DISCLOSURES
  9. REFERENCES

Supported by The University of Texas MD Anderson Cancer Center SPORE in Melanoma grant P50 CA093459.

CONFLICT OF INTEREST DISCLOSURES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. FUNDING SUPPORT
  8. CONFLICT OF INTEREST DISCLOSURES
  9. REFERENCES

Dr. Bassett is supported by a National Cancer Institute (National Institutes of Health) Cancer Center Support Grant. Dr. Gershenwald has acted as a paid consultant for GlaxoSmithKline and Navidea and has received royalties from Mercator Therapeutics. Dr. Kim has acted as a paid consultant for and received clinical trial support from GlaxoSmithKline and Genentech and has acted as a paid member of the Speakers' Bureau for Genentech. Dr. Davies has served on advisory boards for Genentech, GlaxoSmithKline, and Novartis and has received grant support from Genentech, GlaxoSmithKline, Merck, Myriad, Oncothyreon, and AstraZeneca.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. FUNDING SUPPORT
  8. CONFLICT OF INTEREST DISCLOSURES
  9. REFERENCES