**Indications:**  
This is a limited coverage policy for genetic testing of tumor tissue for
somatic mutations in the NRAS gene. The Molecular Diagnostic Program (MolDX)
will cover NRAS testing for metastatic colorectal cancer, per National
Comprehensive Cancer Network (NCCN) guidelines (Version 2. 2016).  
  
All other NRAS testing is non-covered.  
  
 **Background:**  
RAS oncogene is a superfamily of signal transduction proteins, which are
proteins that communicate signals between the cells. Deoxyribonucleic acid
(DNA) mutations in the RAS family genes turns the signals on permanently such
that the cells divide nonstop, leading to cancer. Three of this family's
proteins, HRAS, KRAS, and NRAS are important in tumors and encode 21kD
proteins called p21s.  
  
Previous studies have shown that targeting oncogenic NRAS-driven melanomas
requires decrease in both pERK and pAKT downstream of RAS-effectors for
efficacy, which could be achieved by either targeting both BRAF and CRAF or
BRAF and PIK3CA simultaneously in NRAS mutant tumor cells.  
  
 **Colorectal Cancer:**  
Multiple signaling pathways are involved in colorectal cancer pathogenesis.
The epidermal growth factor receptor (EGFR) plays a key role in activation of
these pathways and is commonly overexpressed in metastatic colorectal cancer
(mCRC). Consequently, EGFR is a target of anticancer therapies. Two of these
drugs, cetuximab and panitumumab, are monoclonal antibodies that block EGFR
action. The 2013 NCCN Clinical Practice Guidelines for Colon Cancer describes
a recent study by Douillard et al7 which reported that 17% of 641 patients
from the PRIME trial without KRAS exon 2 mutations were found to have
mutations in exons 3 and 4 of KRAS or mutations in exons 2, 3, and 4 of NRAS.
A predefined retrospective analysis of a subset of these patients showed that
progression free survival (PFS) and overall survival (OS) were decreased in
those who received panitumumab plus FOLFOX compared to those who received
FOLFOX alone. For this reason, the Food and Drug Administration (FDA)
indication for panitumumab was recently updated to state that panitumumab is
not indicated for the treatment of patients with NRAS mutation-positive
disease in combination with oxaliplatin-based chemotherapy.  
  
In chemotherapy-refractory patients, fewer than 10% of patients who harbor 1
of these mutations respond to EGFR immunotherapy. The American Society of
Clinical Oncology (ASCO) and the NCCN both recommend KRAS mutation testing
prior to prescribing EGFR antagonist therapy for patients with mCRC and state
that alternative therapy should be prescribed when mutations are detected.  
  
However, NCCN Colorectal Guidelines (Version 2.2016) recommend "All patients
with metastatic colorectal cancer should have tumor tissue genotyped for RAS
mutations (KRAS and NRAS) and BRAF mutations. Patients with any known KRAS
mutation (exon 2 or non-exon-2) or NRAS mutation should not be treated with
either cetuximab or panitumumab."3 Evidence increasingly suggests that BRAF
V600E mutation makes response to panitumumab or cetuximab highly unlikely, as
a single agent, or in combination with cytotoxic chemotherapy. In light of the
above, KRAS, NRAS and BRAF are covered for metastatic colorectal cancer.  
  
 **Metastatic Melanoma:**  
The NRAS gene encodes a protein that helps control cell division.
Approximately 15% to 20% of melanomas harbor an oncogenic NRAS mutation. NRAS
mutations can occur in all melanoma subtypes but may be slightly more common
in skin with chronic sun damage or in nodular melanomas. In addition, NRAS
mutations are not found in tumors with BRAF mutations.  
  
Several studies have been carried out to examine whether mutations in BRAF and
NRAS confer different pathological features and clinical behavior. The effect
of these mutations on clinical outcome remains uncertain with previous studies
reporting conflicting results.  
  
(Per NCCN Guidelines 3.2016- BRAF- targeted Therapies: "Approximately half of
patients with metastatic cutaneous melanoma harbor an activating mutation of
BRAF, an intracellular signaling kinase in the MAPK pathway. Most BRAF-
activating mutations occurring in melanomas are at residue V600, usually V600E
but occasionally V600K or other substitutions. BRAF inhibitors have been shown
to have clinical activity in melanomas with BRAF V600 mutations. Inhibitors of
MEK, a signaling molecule downstream of BRAF, may potentiate these effects.
Recent efficacy and safety data from large, randomized trials testing BRAF and
MEK inhibitors have significantly impacted the recommended treatment options
for patients with BRAF-mutation positive advanced melanoma.")16  
  
The NRAS protein is a GTPase which can lead to the activation of other
proteins (such as AKT and MEK) that are also in pathways that help regulate
cell division. In theory, drugs that inhibit AKT or MEK also have the
potential to counteract the effects of NRAS mutations, although NRAS targeting
therapies are still in clinical trials. In addition, pathways that help
regulate cell division also include other proteins that could potentially be
targeted such as PI3K and mTOR.  
  
Melanomas can be tested for NRAS mutations with targeted sequencing. There are
several manufacturers of targeted genetic tests that can detect NRAS mutations
in melanoma tumor samples. The prognostic significance of NRAS mutations is
still not well understood and further investigation of the histologic types of
melanomas with specific NRAS mutations in a larger series is necessary to
validate these apparent impacts on patient outcomes. In smaller subsets of
cutaneous melanoma, other activating mutations have been described, including
NRAS, cKIT, and CDK4.  
  
 **Other Cancers:**  
Other neoplastic diseases in which NRAS mutations have been reported in the
primary literature include: myeloid leukemia, bladder cancer, liver cancer,
and proliferative thyroid lesions.  
  
Schulten et al17 directly sequenced mutational hotspot regions encompassing
codons 12, 13, and 61 of the RAS genes in 381 cases of thyroid lesions. In
addition, the putative NRAS hotspot region encompassing codon 97 was sequenced
in 36 thyroid lesions. Schulten and team found mutations in 16 out of 57
patients.17  
  
Kompier et al13 reports that although they have been reported, NRAS mutations
are not common in bladder cancer.  
  
Although NRAS mutations have been identified in the above tumor types,
evidence in the primary literature is limited with regard to the clinical
utility of NRAS mutation testing and its impact on management and survival.
There is currently insufficient evidence to demonstrate clinical utility of
NRAS testing in these tumor types.  
  
 **NRAS Testing in relation to Noonan syndrome diagnosis:**  
Noonan syndrome is a common autosomal dominant condition with an incidence of
1/1,000 to 1/2,500 people. Unlike the somatic tumor mutations discussed above,
Noonan syndrome may be caused by a germline mutation in the NRAS gene which
would be present in every cell of the body. Noonan syndrome is characterized
by a number of phenotypic findings including distinctive facial features,
short stature, heart defects, cryptorchidism, lymphedema, and coagulation
defects, among others. Several syndromes have features that overlap clinically
with Noonan syndrome including cardiofaciocutaneous syndrome, Costello
syndrome, LEOPARD syndrome and Noonan-like syndrome with loose anagen hair.
The genetic etiologies of these conditions can also overlap with Noonan
syndrome.  
  
Several of these disorders have been referred to as neurocardiofacialcutaneous
syndromes, RASopathies or Ras/MAPK pathway disorders and have a shared pathway
of genetic function.  
  
They are characterized by facial dysmorphism, cardiac disease, reduced growth,
skeletal and ectodermal defects and variable cognitive deficits. They also
share a predisposition to development of malignancies.  
  
Overall, approximately 75% of individuals with Noonan syndrome will have an
identifiable mutation with gene panel testing. To date, NRAS mutations have
been found in 4 individual case reports which suggests that NRAS testing for
Noonan syndrome is unlikely to yield positive results. The clinical features
appear to be typical with no particular or distinctive phenotype observed
suggesting that mutation testing targeted to select individuals is not
feasible.  
  
Genotype/phenotype correlations have emerged that can help to direct medical
management for those affected with an associated condition, but not
specifically for NRAS mutations. For instance, mutations in the SOS1 gene have
been associated with an increased chance for ectodermal involvement,
development of certain solid tumors, pulmonary stenosis, and atrial and
ventricular septal defects; with an associated decreased prevalence of
cognitive defects, short stature, and hypertrophic cardiomyopathy.  
  
Medical management recommendations are available for many of the Noonan
syndrome spectrum disorders. Overlapping features result in overlapping
medical management recommendations, typically guided by clinical features.

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