Ther Adv Med Oncol
(2012) 4(2) 61 –73
© The Author(s), 2011.
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Therapeutic Advances in Medical Oncology Review
Malignant melanoma is the sixth most common
type of new cancer in the UK and the fifth most
common in the USA [National Cancer Institute,
2010]. Although it is the least common skin cancer,
cutaneous melanoma is the most life threatening
with metastases present in 10–15% of patients at
diagnosis [National Cancer Institute - Surveillance
Epidemiology and End Results, 2010]. The annual
incidence of melanoma is escalating and in the UK
the incidence rates have increased more rapidly
than any of the top 10 cancers in men and women
[Cancer Research UK, 2010]. Patients with
advanced or metastatic disease confined to the skin,
subcutis and lymph nodes have a median overall
survival (OS) of 12 months compared with only
4–6 months for patients with visceral disease [Balch
et al. 2001]. In this setting, the reported OS rates
from studies with various chemotherapeutic agents,
including dacarbazine and temozolamide, as well as
immune modulators, is between 6 and 10 months
[Chapman et al. 1999; Eigentler et al. 2003;
Middleton et al. 2000]. The cytotoxic T-lymphocyte
antigen 4 (CTLA-4) antibody, ipilimumab, was the
first agent to demonstrate a benefit in OS in previ-
ously treated metastatic melanoma [Hodi et al.
2010] and more recently in the first-line setting in
combination with dacarbazine [Robert et al. 2011].
In addition, the selective v-raf murine sarcoma viral
oncogene homolog B1 (BRAF) inhibitor, vemu-
rafenib (PLX4032), has also demonstrated an OS
benefit compared with dacarbazine in the first-line
setting [Chapman et al. 2011]. Thus, it is the advent
of immunotherapy and agents targeting specific
genetic aberrations that have significantly improved
outcomes in malignant melanoma.
Melanoma: a heterogeneous disease
Although genetic aberrations and abnormal
activity in the mitogen-activated protein kinase
(MAPK) pathway drive tumourigenesis in the
majority of cutaneous melanomas, there is an
increasing body of evidence that other pathways
and immunological mechanisms contribute to its
Aberrant activation of the MAPK pathway has
been demonstrated in over 80% of cutaneous
melanomas due to abnormalities at various levels
along the RAS-RAF-MEK-ERK pathway [Platz
et al. 2008].
The potential for BRAF V600 inhibitors in
advanced cutaneous melanoma: rationale
and latest evidence
Charlotte Lemech, Jeffrey Infante and Hendrik-Tobias Arkenau
Abstract: Historically, patients with advanced cutaneous melanoma have a poor prognosis
and limited treatment options. The discovery of selective v-raf murine sarcoma viral
oncogene homolog B1 (BRAF) V600 mutation as an oncogenic mutation in cutaneous
melanoma and the importance of the mitogen-activated protein kinase (MAPK) pathway in
its tumourigenesis have changed the treatment paradigm for melanoma. Selective BRAF
inhibitors and now MEK inhibitors have demonstrated response rates far higher than
standard chemotherapeutic options and we review the phase I–III results for these agents
in this article. The understanding of mechanisms of resistance that may occur upstream,
downstream, at the BRAF level or bypassing the MAPK pathway provides a platform for
rational drug development and combination therapies.
Keywords: BRAF inhibitor, BRAF V600E, cutaneous melanoma, ipilimumab, MEK inhibitor,
Sarah Cannon Research
UK, 93 Harley Street,
London W1G 6AD, UK; and
University College London,
Charlotte Lemech MBBS
Sarah Cannon Research
UK, London and University
College London, London,
Jeffrey Infante MD
Sarah Cannon Research
Institute, Nashville, TN,
Therapeutic Advances in Medical Oncology 4 (2)
Activation of the Rat Sarcoma (RAS) family
GTPases by growth factors or by RAS mutation is
the first step driving this pathway. Activated RAS
proteins can complex with and activate members
of the RAF kinase family (ARAF, BRAF and
CRAF), causing subsequent phosphorylation
and activation of MEK 1 and MEK2, followed by
extracellular signal-regulated kinases (ERK1 and
ERK2) [Davies et al. 2002]. In turn, this leads to
phosphorylation of the erythroblast transformation
specific (ETS) protein family, nuclear transcrip-
tion factor activation, expression of cell-cycle
regulators such as cyclin D, finally leading to
cell-cycle progression and regulation of cellular
differentiation, senescence and apoptosis/survival
[Platz et al. 2008]. Although activity along this
pathway is essential for normal cell function,
abnormal activation of the MAPK pathway due
to mutations and aberrations at various levels has
been implicated in a number of cancer types, not
only malignant melanoma but also colorectal
cancer and borderline ovarian cancer, among
others [Davies et al. 2002].
Mutations along the MAPK pathway and other
genetic alterations have been documented in
varying frequencies in primary and metastatic
melanomas based on site, previous sun exposure,
skin damage and other factors [Curtin et al. 2005,
Long et al. 2011a].
The BRAF mutation is among the most studied,
occurring in 36–59% of primary melanomas
and 42–66% of metastatic melanomas [Houben
et al. 2004; Jakob et al. 2011; Long et al. 2011a]
and has been characterized as an oncogenic
mutation [Davies et al, 2002.; Karasarides et al.
2004]. The BRAF mutation has been demon-
strated to occur more frequently in intermit-
tently sun-exposed sites (i.e. trunk) and sites
without chronic sun-induced damage and are
also present in 10–15% of primary cases of
mucosal and acral melanomas [Curtin et al.
2005; Long et al. 2011a].
In contrast, mutational analyses of melanoma in
patients with high sun exposure and chronic sun-
induced skin damage more often have high cyclin
D1 (CCND1) and cyclin-dependent kinase 4
(CDK4) gene copy numbers. Increased CCND1
copy number has also been demonstrated in
acral melanoma (44%), lentigo maligna melanoma
(10%) and superficial spreading melanoma (6%)
[Sauter et al. 2002].
Another frequently occurring mutation is the
CKIT mutation, specifically in melanomas of both
ultraviolet (UV)-protected sites, acral and mucosal
melanomas (in 36% and 39%, respectively), as well
as melanoma on chronically sun-damaged skin
(28%) [Curtin et al. 2006].
Increased copy number of GAB2, a scaffolding
protein that mediates interactions with various
signalling pathways, including RAS-RAF-MEK-
ERK and phosphoinositide 3-kinase (PI3K)-
AKT signalling, has also been demonstrated in up
to 26% of acral and mucosal melanomas and is
mutually exclusive of BRAF, NRAS and KIT
mutations [Chernoff et al. 2009]. NRAS muta-
tions have been demonstrated in 20–29% of
melanomas of all subtypes and are associated
with a higher Clark level of invasion and older age
compared with BRAF mutation tumours [Curtin
et al. 2006; Edlundh-Rose et al. 2006].
Improved understanding of the genetic heteroge-
neity in melanoma, the detection of oncogenic
mutations and the ability to target these mutations
has dramatically expanded the treatment options
available for this disease.
Types of BRAF mutations
BRAF is a serine/threonine protein kinase, encoded
on chromosome 7q34, that activates the MAPK/
ERK signalling pathway. There are now over 100
somatic mutations identified in BRAF [Wellcome
Trust Sanger Institute, 2011].
The most common somatic mutation, found in
66–90% of BRAF-mutant melanomas [Cheng
et al. 2011; Wellcome Trust Sanger Institute,
2011; Long et al. 2011a], occurs in the activating
segment in exon 15 and involves the substitution
of glutamic acid for valine at codon 600 (GTG
to GAG, known as V600E] [Davies et al. 2002;
Platz et al. 2008]. This leads to elevated kinase
activity compared with BRAF wild type (wt) dis-
ease, stimulated phosphorylation of downstream
endogenous ERK and subsequent cellular prolif-
eration and survival [Davies et al. 2002; Dhomen
and Marais, 2009].
A number of other clinically relevant, but less
common mutations have also been described,
including V600K and V600G/R. The V600K
mutation has been reported in 16–30% of patients
with BRAF-mutant metastatic melanoma [Cheng
C Lemech, J Infante et al.
et al. 2011; Long et al. 2011; Rubinstein et al.
2010; Thomas et al. 2007]. It involves two point
mutations (GTG to AAG) resulting in a substi-
tution of lysine for valine. The frequency of
non-V600E mutations is particularly important
when interpreting the clinical trials of the BRAF
inhibitors, which vary in the mutation subtypes
that are included.
In primary melanomas, BRAF-mutant status has
been associated with younger age (age ≤40 years),
histopathologic subtype (superficial spreading
and nodular melanoma), presence of mitoses,
single or occult primary melanoma and truncal
location [Long et al. 2011b]. Recent data in
patients with advanced disease demonstrate BRAF
mutation rates greater than 80% in those less than
40 years, with V600E more common at younger
ages and V600K more common at older ages
[Menzies et al. 2011]. Other reported associated
factors include fewer markers of chronic sun
damage in surrounding skin, higher total body
nevus counts, early life UV exposure and histo-
pathologic findings, including heavy melaniza-
tion and prominent upward scatter of melanocytes
[Liu et al. 2006; Thomas et al. 2007; Viros et al.
BRAF mutations are a negative marker for sur-
vival with a strong association with inferior OS
demonstrated in the metastatic setting [Houben
et al. 2004; Long et al. 2011b; Flaherty, 2011]. It
has also been demonstrated that patients with
BRAF mutation treated with a BRAF inhibitor
have an improved OS compared with those with
BRAF wt and BRAF-mutant status not receiving
a BRAF inhibitor [Long et al. 2011a], findings
which have been confirmed in later phase trials.
Early preclinical studies of RAF inhibition
demonstrated that specific inhibitory nucleic
acids or chemical RAF inhibition in cell lines
and xenograft models caused growth arrest and
induction of apoptosis [Calipel et al. 2003;
Hoeflich et al. 2006].
The earliest clinical trials of RAF inhibition with
metastatic melanoma involved the multiple tyros-
ine kinase inhibitor sorafenib. Although it was ini-
tially developed as a RAF inhibitor, sorafenib has
inhibitory effects on vascular endothelial growth
factor receptor 2 (VEGFR2), VEGFR3, platelet-
derived growth factor receptor β (PDGFRβ),
cKIT and fms-like tyrosine kinase receptor 3
(FLT3). A randomized phase II study of sorafenib
showed disease stabilization in a few unselected
patients with advanced melanoma, but without
any impact on survival [Eisen et al. 2006]. Another
phase II study of sorafenib in combination with
dacarbazine in patients with untreated melanoma
showed an improvement in median progression-
free survival (PFS), but this did not translate into
an OS benefit [McDermott et al. 2008]. In addi-
tion, there was no activity demonstrated in a
phase III trial in the second-line setting combining
sorafenib with carboplatin and paclitaxel [Hauschild
et al. 2009].
The two most advanced agents currently in
clinical development are the selective BRAF
inhibitors, vemurafenib (PLX4032, RG 7204)
and GSK2118436 (GSK436).
Vemurafenib is an orally available, highly potent,
ATP-competitive inhibitor of mutant BRAF. The
phase I (dose extension phase), II and III trials for
this agent included patients with BRAF V600E-
mutant metastatic melanoma, confirmed by
means of a polymerase chain reaction (PCR)
assay (cobas 4800 BRAF V600 Mutation Test,
Roche Molecular Systems Inc., Pleasanton, CA,
USA). This assay involves hybridizing a probe,
specific to the 1799T→A substitution that results
in the V600E BRAF mutation, with DNA isolated
from formalin-fixed, paraffin-embedded tumour
tissue and determining the presence or absence of
amplification after repeated chain-reaction cycles.
Patients with other DNA alterations giving rise
to V600E and non-V600E mutations were thus
The phase I study included a dose-escalation
phase (from 160 mg twice daily to 1120 mg twice
daily) and dose-extension phase (recommended
phase II dose of 960 mg twice daily) and demon-
strated a response rate (RR) of 69% (11 of 16
patients) in the dose-escalation phase and 81%
(26 of 32 patients) in the dose-extension phase.
At the time of publication, the estimated median
PFS was more than 7 months with duration of
response ranging from 2 months to over 18
months [Flaherty et al. 2010].
The subsequent BRAF in Melanoma 2 (BRIM-
2) phase II study included 132 patients and
showed RR of 53%, stable disease (SD) in a fur-
ther 29%, median PFS of 6.7 months and OS at
6 and 12 months of 77% and 58%, respectively.
Therapeutic Advances in Medical Oncology 4 (2)
At the time of the report, the median OS had not
been reached [Ribas et al. 2011].
The recent phase III BRAF Inhibitor in Melanoma
3 trial (BRIM-3) compared vemurafenib (960 mg
twice daily) with dacarbazine (1000 mg/m2) as
first-line treatment in patients with BRAF V600E-
mutant metastatic melanoma [Chapman et al.
2011]. The RR was 48% for vemurafenib and
5% for dacarbazine with a significant prolonged
median PFS of 5.3 months in the vemurafenib
arm compared with 1.6 months on dacarbazine
[hazard ratio (HR) 0.26; 95% confidence interval
(CI) 0.20–0.33, p < 0.0001]. Treatment with
vemurafenib resulted in a 63% relative risk reduc-
tion for death and a 74% risk reduction for either
death or disease progression. At 6 months, the OS
was 84% for patients who received vemurafenib
compared with 64% for patients who received
dacarbazine. The adverse events (AEs) were con-
sistent with those previously described in earlier
trials and included grade 2 (G2) and G3 arthral-
gias (18% and 3%), rash (10% and 8%), photo-
sensitivity (12% G2 or G3), fatigue (11% and
2%), cutaneous squamous-cell carcinoma (SCC,
12%), keratoacanthoma (2% and 6%), nausea
(7% and 1%) and diarrhoea (5% and <1%). Dose
interruption and modification were required in
38% of patients.
Interestingly, BRIM-3 also included 10 patients
with a V600K mutation, 4 of whom demonstrated
a good clinical response. Comparison of the PCR
assay (cobas 4800 BRAF V600 Mutation Test)
and Sanger sequencing has demonstrated higher
sensitivity in the detection of V600E mutations
with the PCR test; however, 6.8% of samples
identified by the PCR assay were shown to have a
V600K rather than V600E mutation, confirmed
on Sanger sequencing [Bloom et al. 2011].
GSK436 is an ATP-competitive, reversible inhib-
itor of mutant BRAF V600E, as well as V600K
and V600G kinases. A phase I–II trial enrolled 61
patients including 52 with BRAF-mutant mela-
noma [Kefford et al. 2010]. There was a high RR
with 18 of 30 patients (60%) demonstrating par-
tial response (PR) at first restaging during weeks
8–9. The PFS at the expanded dose of 150 mg
twice daily was 8.3 months.
In the dose expansion cohort of 20 patients, 77%
had a BRAF V600E mutation and 19% had a
V600K mutation [Kefford, 2010]. Patients with a
BRAF V600E mutation demonstrated RR of 77%
and the subgroup of patients with a V600K muta-
tion demonstrated a RR of 44% (four of nine).
Overall GSK436 was very well tolerated with
side effects similar to those described with
vemurafenib, including skin changes (37%, one
G3), low-grade cutaneous SCC (two patients),
headache (19%, one G3), nausea (18% G1),
fatigue (15% G1) and vomiting (13%, four G2).
Although the majority of side effects are similar
between the two BRAF inhibitors, vemurafenib
is associated with photosensitivity in up to 30%
of patients (12% G2 or G3) while pyrexia is
reported in 15% (2% G3) on GSK436.
Interestingly, in the dose-escalation phase with
GSK436, a cohort of 10 patients with previously
untreated brain metastases also demonstrated a
significant RR to treatment. There was a reduction
in size of the brain metastases in 9 of 10 patients,
ranging from a 20% to a 100% reduction in brain
metastases that were 3–15 mm in size prior to
treatment. The reduction in brain metastases
correlated with extra-cranial response [Long et al.
Further studies of GSK436 that have completed
accrual and may be reported in 2012 include
GSK436 versus dacarbazine in previously untreated
patients with BRAF-mutant advanced or meta-
static melanoma, as well as a study of GSK436 in
BRAF-mutant metastatic melanoma to the brain
[ClinicalTrials.gov Identifier NCT01227889].
Importantly, the response to BRAF inhibition
with improvement in symptoms and performance
status is usually rapid, occurring within the
first 2 weeks, and has shown concordance with
fluorodeoxyglucose positron emission tomogra-
phy (FDG-PET) response [McArthur et al.
2010]. Interestingly, heterogeneous FDG-PET
response at day 15 of treatment has been demon-
strated in up to 26% of patients in a substudy of
23 patients, with significantly shorter time to
progression compared with those with a homog-
enous FDG-PET response [Carlino et al. 2011].
As evidenced with both selective BRAF inhibi-
tors, though less commonly with GSK436
[Kefford et al. 2010], the increased incidence
of cutaneous SCC generally develops between
weeks 2 and 14 and is hypothesized to be due to
upstream RAS mutations in pre-existing SCC
skin lesions, occurring in approximately 15% of
patients. Selective inhibition of downstream BRAF
C Lemech, J Infante et al.
can lead to CRAF signalling by mutant RAS with
subsequent development of SCCs [Arkenau et al.
2010]. The majority of these SCCs are keratoa-
canthoma type, well differentiated with no meta-
static potential and can be treated with surgical
excision [Flaherty et al. 2010].
In addition to inhibiting BRAF signalling with
selective BRAF inhibitors, preclinical and clini-
cal evidence also supports the antiproliferative
activity of MEK inhibitors in melanoma [Zhang
et al. 2003].
The earliest MEK inhibitors in preclinical and
clinical development were PD98059, UO126
and CI-1040 [Messersmith et al. 2006]; however
limited clinical activity did not warrant further
investigation of these agents.
PD0325901 was a second-generation MEK
inhibitor also evaluated in phase I and II trials with
some preliminary evidence of response and disease
stabilization in patients with metastatic melanoma
[Lorusso et al. 2005]. Dose-limiting diarrhoea and
rash prevented further dose escalation and phase II
trials were suspended due to the occurrence of reti-
nal vein thrombosis in several patients.
AZD6244 was another MEK inhibitor assessed
in early phase trials. The phase I trial enrolled
57 patients, 20 of whom (35%) had melanoma
[Adjei et al. 2008]. One patient had an objective
response and seven patients achieved disease
stabilization after two cycles. A further rand-
omized phase II study comparing AZD6244 and
temozolamide demonstrated an RR of 12% (5
of 42 patients) in BRAF-mutant metastatic mel-
anoma [Dummer et al. 2008] but no significant
difference in the primary endpoint of PFS.
Further single-agent clinical trials have not been
pursued but phase II combination trials with
dacarbazine, docetaxel and temsirolimus are
currently underway in BRAF-mutant metastatic
melanoma in the first-line setting [ClinicalTrials.
gov Identifier NCT00936221, ClinicalTrials.
gov Identifier NCT01256359, ClinicalTrials.
gov Identifier NCT01166126 respectively.].
The phase I–II study of the MEK inhibitor
GSK1120212 in patients with advanced BRAF-
mutant melanoma showed good tolerability and
encouraging RRs. At the recommended phase II
dose of 2 mg once daily, RRs were 40% (8 of 20
patients) and a further 18% had SD [Falchook
et al. 2010].
The most common AEs were an acneiform rash
(all grade 85%; ≥G3 2%) usually on the face,
torso and arms, diarrhoea (all grade 48%; ≥G3
2%), fatigue (all grade 37%; ≥G3 7%) and nausea
(all grade 20%; ≥G3 0). Less common events
requiring monitoring in future studies included
left ventricular systolic dysfunction (9 of 162
patients), central serous retinopathy (3 of 162
patients, at dose levels higher than 2 mg daily)
and retinal vein occlusion (1 of 162 patients at
2 mg daily). Importantly, central serous retinopa-
thy is reversible on drug cessation [Infante et al.
2010]. Retinal vein occlusion is not reversible;
however, the one patient affected had a significant
improvement in vision with intraocular anti-
VEGF therapy [Infante et al. 2010].
Further single-agent activity is being assessed in
an ongoing phase III trial, randomizing patients
to GSK1120212 versus first or second-line
Combination therapy with MEK and
There is early clinical evidence that the combina-
tion of BRAF and MEK inhibitors shows clinical
activity in BRAF V600-mutant melanoma with
a lower incidence of rash and BRAF-induced
hyperproliferative skin lesions [Infante et al. 2011].
The rationale for combining both agents is based
on preclinical studies that demonstrate potential
reduction in drug resistance as well as decreased
incidence of BRAF inhibitor induced hyperprolif-
erative skin changes and SCCs. Preliminary results
at doses of GSK436 150 mg twice daily and
GSK1120212 2 mg daily (19 patients) showed a
complete response (CR) rate of 11%, a total RR
(CR + PR) of 74% and clinical benefit rate (CR +
PR + SD) of 100%. Compared with single-agent
toxicities there was also a lower incidence of rash
(all grade 25%; ≥G3 2%) and hyperproliferative
skin lesions. Other common G2 toxicities were
pyrexia (11%), vomiting (4%) and fatigue (4%).
Significantly, only 1 of 109 patients developed cuta-
neous SCC, supporting the preclinical evidence
that the combination leads to reduction of SCCs,
potentially by switching off the CRAF-activated
pathway through downstream MEK inhibition.
A number of clinical trials assessing the combi-
nation of BRAF and MEK inhibitors or the