This policy provides coverage for multi-gene non-next generation sequencing
(NGS) panel testing and NGS testing for the diagnostic workup for
myeloproliferative disease (MPD), also known as myeloproliferative neoplasms
(MPNs), and limited coverage for single-gene testing of patients with BCR-ABL
negative MPD. BCR-ABL negative MPD includes polycythemia vera (PV), essential
thrombocythemia (ET), and primary myelofibrosis (PMF).

For laboratories performing single gene technologies, a sequential genetic
testing approach is expected. Once a positive result is obtained and the
appropriate diagnosis is established, further testing should stop. Reflex
testing to the next gene will be considered reasonable and necessary if the
following sequence of genetic tests produce a negative result:

  1. BCR-ABL negative test results, progress to #2
  2. JAK 2, cv negative test results, progress to #3 or #4
  3. JAK, exon 12 (JAK2 exon 12 is only done when PV is suspected)
  4. Calreticulin (CALR)/MPL (CALR/MPL is only done when either ET or PMF is suspected; testing for CALR/MPL does NOT require a negative JAK2 exon 12, just a negative JAK2 V617F result)

Genetic testing of the JAK2 V617F mutation is medically necessary when the
following criteria are met:

  * Genetic testing impacts medical management; **and  **
  * Patient would meet World Health Organization's (WHO) diagnostic criteria for myeloproliferative disease (i.e., PV, ET, PMF) **if** JAK2 V617F were identified.

Genetic testing of JAK2 exon 12, performed to identify PV, is medically
necessary when the following criteria are met:

  * Genetic testing impacts medical management; **and**
  * Patient would meet WHO's diagnostic criteria for PV, if JAK2 exon 12 testing were positive; **and**
  * JAK2 V617F mutation analysis was previously completed and was negative.

Genetic testing of the CALR gene (only found in ET and PMF) is medically
necessary when the following criteria are met:

  * Genetic testing impacts medical management; **and**
  * JAK2 V617F mutation analysis was previously completed and negative; **and**
  * Patient would meet WHO's diagnostic criteria for MPD (i.e. ET, PMF) if a clonal marker were identified.

Genetic testing of the MPL gene is medically necessary when the following
criteria are met:

  * Genetic testing impacts medical management; **and**
  * JAK2 V617F mutation analysis was previously completed and negative; **and**
  * Patient would meet WHO's diagnostic criteria for MPD (i.e., ET, PMF) if a clonal marker were identified.

Note: In a single-gene sequential approach (not mandated by this policy), CALR
would be a higher priority single gene test than MPL because:

  * CALR mutations is more prevalent than MPL mutations in ET/PMF patients; and 
  * CALR mutations are reported to predict a more indolent disease course than that of patients with JAK2 mutations.

For laboratories performing NGS or "hotspot" testing platforms: Molecular
testing for BCR-ABL, JAK 2, JAK, exon 12, and CALR/MPL genes by NGS is covered
as medically necessary for the identification of myeloproliferative disorders.

**Myeloproliferative Disorders**  
Myeloproliferative disorders are a group of conditions that cause abnormal
growth of blood cells in the bone marrow. They include PV, ET, PMF, and
chronic myelogenous leukemia (CML). The WHO further classifies PV, ET, and PMF
as Philadelphia chromosome negative myeloproliferative neoplasms (MPNs). The
diagnosis of an MPN is suspected based upon clinical, laboratory, and
pathological findings (i.e., bone marrow morphology). MPNs are related, but
distinct from, myelodysplastic syndromes (MDS). In general, MDS are
characterized by ineffective or dysfunctional blood cells, while MPN are
characterized by an increase in the number of blood cells.

**Polycythemia Vera (PV)**  
PV is a chronic MPD characterized by increased hemoglobin, hematocrit, and red
blood cell mass. There is an associated increased risk for thrombosis and
transformation to acute myelogenous leukemia (AML) or PMF; however, patients
are often asymptomatic. Criteria for a diagnosis of PV are based upon complete
blood count (CBC) and clinical features. The JAK2 V617F mutation is present in
the vast majority of PV, accounting for approximately 90% of cases.
Functionally similar mutations in JAK2 exon 12 account for most remaining
cases of JAK2 V617F mutation-negative PV. Together, they are identified in 98%
of PV cases and lead to high diagnostic certainty.

Among the proposed revised WHO criteria for diagnosis is presence of the
somatic JAK2 V617F mutation or functionally similar exon 12 mutation. Absence
of a JAK2 mutation, combined with normal or increased serum erythropoietin
level, greatly decreases the likelihood of a PV diagnosis. WHO proposed
revision criteria for PV do not address additional molecular markers,
including CALR mutation status.

**Essential Thrombocythemia (ET)**  
ET is a disorder of sustained increased platelet count. The majority of ET
patients (60%) carry a somatic JAK2 V617F mutation, while a smaller percentage
(5-10%) have activating MPL mutations. Revision to the WHO criteria for
diagnosis of ET has been proposed and includes exclusion of PV, PMF, CML, MDS,
or other myeloid neoplasm. Also included in the proposed major criteria for
diagnosis is demonstration of somatic JAK2 V617F mutation or MPL exon 10
mutation.12 Proposed criteria additionally state that 70% of patients without
a JAK2 or MPL mutation carry a somatic mutation of the calreticulin gene.
Among confirmed ET cases, mutations in CALR are more common than MPL. Positive
CALR mutation status is suggested as indicating a more indolent course.5

**Primary Myelofibrosis (PMF)**  
PMF is a rare disorder in which the bone marrow is replaced with fibrous
tissue, leading to bone marrow failure. Clinical features are similar to ET.
The approximate incidence is 1 in 100,000 individuals. Persons can be
asymptomatic in the early stages of the disease. For such patients, treatment
may not initially be necessary. Progression of the disease can include
transformation to AML. Treatment is generally symptomatic and aimed at
preventing complications.

Demonstration of a clonal marker is important for diagnosis. Somatic molecular
markers in PMF patients are similar to those in patients with ET, and include
JAK2 V617F, MPL, and CALR. Somatic mutations in JAK2 are identified in 50-60%
of PMF cases, and MPL mutations in 10%. Mutations in CALR are less common than
JAK2, but more common than MPL.

**Molecular Genetic Testing**  
One JAK2 gene mutation, V617F, is most commonly reported, occurring in over
90% of all PV cases and about 50% of ET cases. Testing for JAK2 V617F gene
mutations can be useful in diagnosis and is incorporated into the WHO's
diagnostic criteria for these conditions.

The thrombopoietin receptor MPL is one of several JAK2 cognate receptors and
is considered essential for myelopoiesis. The mutation frequency of MPL
mutations associated with myeloproliferative disorders is substantially less
(<10%) than JAK2 mutations. The guideline group for the British Committee for
Standards in Haematology recommended a modification to the 2008 WHO criteria
for ET to include the presence of an acquired pathogenetic mutation (e.g., in
the JAK2 or MPL genes).3 Therefore, MPL gene testing may be indicated for
individuals who would meet WHO's diagnostic criteria for MPD if a clonal
marker were identified.

CALR mutations have been identified in patients with MPNs and recent studies
have investigated the utility of CALR mutation testing for the diagnosis and
classification of MPNs. The mutations themselves are variable; however,
generally focused in the exon 9 region.

Studies have shown that a significant proportion of patients with MPNs and
normal JAK2 V617F mutation testing have a CALR gene mutation. CALR mutations
account for a large proportion of JAK2/MPL-negative ET and PMF cases.
Approximately 60% of JAK2/MPL-negative ET patients are CALR-positive and 30%
of JAK2/MPL-negative PMF patients are CALR-positive. Overall, CALR mutations
are identified in approximately 21% of ET cases and 16% of PMF cases. CALR
mutations have not been reported in PV case series.2

For this reason, CALR gene testing may be indicated for individuals who would
meet WHO's diagnostic criteria for MPD if a clonal marker were identified.
Proponents have argued for revised WHO criteria that includes CALR mutation
status in the classification system for ET and PMF.12 Current National
Comprehensive Cancer Network (NCCN) guidelines do not make recommendations
for CALR genetic testing; however, these guidelines are specific to MDS and do
not broadly address MPNs, such as ET or PMF. Somatic mutations in non-MDS
genes, such as CALR, are listed as being associated with conditions that can
mimic other myelodysplastic syndromes.

Aside from diagnostic utility, some research suggests distinct clinical
outcomes associated with CALR mutation status; however, the findings have not
been confirmed in other studies. It is suggested that ET patients with CALR
mutations have lower polycythemic transformation rates, but not lower
myelofibrotic transformation rate, compared with ET patients harboring a JAK2
mutation. Others reported a higher platelet count, younger age of diagnosis,
lower leukocyte count, and decreased risk for thrombosis, compared with a JAK2
positive ET population.1 CALR-mutated ET has also been associated with better
thrombosis-free survival and lower leukocyte counts; overall survival has been
reported as not different among CALR mutated and non-mutated ET.2,15

Although they are useful for establishing a diagnosis, the presence of
specific clonal markers does not dictate treatment. Controversy exists
generally regarding the treatment of asymptomatic individuals with ET. Some
argue against treatment if there are no associated complications. In general,
the main goal of treatment with PV and ET is to identify persons at high risk
for thrombosis and prevent complications. Persons with PV and ET are
determined to be at high-risk due to age >60 years and past history of
thrombotic event(s). CALR mutational status is not currently used for risk
stratification.11

Level of evidence  
Quality - Strong  
Strength - Strong  
Weight - Moderate

In summary, multiple studies have demonstrated the diagnostic value of CALR
mutation status in a population of JAK2 and MPL negative patients with
suspected ET and PMF. The presence of a somatic CALR mutation can prove useful
in obtaining an accurate diagnosis. Emerging evidence suggests possible
differences in clinical phenotype among the associated clonal markers,
including CALR-positive ET cases. However, CALR mutation status is currently
not incorporated into clinical risk stratification and more research is needed
in this area.