This policy provides coverage for indicated fluorescent in situ hybridization
(FISH) probes for patients whose bone marrow examination is suggestive of
myelodysplasia (MDS) and who have an inadequate cytogenetic assessment by
conventional karyotyping. In general, conventional karyotype analysis is
sufficient for confirmation for the diagnosis of MDS. MDS FISH studies should
only be performed when there are fewer than 20 metaphases available for
analysis, or an unresolved karyotype. Medicare will only cover up to 4 FISH
studies (-7 or del(7q), -5 or del(5q), +8 and del(20q)) on initial evaluation
to diagnose MDS. Reflex testing for additional FISH markers to diagnose MDS is
only reasonable and necessary when the initial 4 studies are negative, or the
diagnosis remains uncertain following the initial 4 probes.

Generally, FISH testing is not reasonable and necessary for diagnosing MDS and
provides little if any additional information to conventional karyotyping.

The myelodysplastic syndromes (MDS) represent a spectrum of clonal bone marrow
diseases with heterogeneous presentations. The classic triad for MDS includes
1 or more cytopenias, defective differentiation (dysplasia) of 1 or more blood
cell lines and marrow hypercellularity. Over time, there is an increased rate
of progression to acute myeloid leukemia (AML). These secondary AML cases
carry a worse prognosis than de novo AML cases. Furthermore, there are myeloid
neoplasms that share overlapping characteristics with both MDS and
myeloproliferative neoplasms (MPNs), such as chronic myelomonocytic leukemia
(CMML). The World Health Organization (WHO) has designated these diseases
separately as MDS/MPNs, distinct from either MDS or MPNs.(1)  
  
According to the 2016 National Comprehensive Cancer Network (NCCN) Guidelines,
the overall incidence of MDS is approximately 5/100,000 per year, primarily in
adults. MDS is rare in patients under the age of 40, but much more common in
older patients. The incidence of MDS among patients 70-79 years of age is
30/100,000, and in patients > 80 years the incidence is 60/100,000.(2)

MDS has historically been classified by a combination of traditional
laboratory techniques, such as demonstration of stable cytopenias by complete
blood count, microscopic examination of a bone marrow biopsy, and bone marrow
cytogenetic (conventional karyotype) studies. Other than the clinical feature
of the number of cytopenias and specific cytogenetic changes found recurrently
in MDS, all other diagnostic criteria in MDS rely upon light microscopy
findings. These include the dysplastic changes on 1 or more cell lineages of
megakaryocytes, erythrocytes and granulocytes; increased myeloblasts; and/or
presence of ringed sideroblasts. Low-risk MDS is associated with dysplasia
affecting only 1 cell lineage, with or without ringed sideroblasts, and
isolated deletions involving the long arm of chromosome 5 (5q-). High-risk
disease is associated with dysplasia across multiple lineages, increased blast
percentages, and complex karyotype.

Neither the 2016 WHO Classification of MDS, the International Prognostic
Scoring System (IPSS) nor the Revised IPSS (IPSS-R) require the use of
additional MDS-associated mutations to establish a diagnosis of MDS. As noted
in NCCN 2017 Guidelines, "Bone marrow or peripheral blood cells may be assayed
for MDS-associated gene mutations. These can establish the presence of clonal
hematopoiesis which can help exclude benign causes of cytopenia with non-
diagnostic morphology but do not establish the diagnosis of MDS in the absence
of clinical diagnostic criteria."

**Cytogenetic Testing (Chromosome Analysis)**

Conventional cytogenetic testing (routine chromosome analysis) is also
referred to as karyotyping and is the most important special study for the
diagnosis of MDS. The identification of clonal cytogenetic abnormalities,
except for +8, del(20q) and -Y, can serve as presumptive evidence of MDS. In
decreasing order of frequency, the most frequent chromosomal abnormalities
associated with MDS are: -7 or del(7q), -5 or del(5q), +8 and del(20q). A more
comprehensive list of chromosomal abnormalities associated with MDS is
available from the WHO.(3)

Cytogenetic studies are used to detect numerical and/or structural chromosome
abnormalities in metaphase cells in constitutional conditions, such as
congenital conditions (Down's syndrome) and acquired conditions associated
with neoplastic or cancer processes. Conventional chromosome analyses require
some form of cell culture, followed by chromosome harvesting, chromosome
banding, microscopic analysis and karyotype production. Depending on the
application, detection of structural chromosome changes, resulting in a loss
or gain of genetic material by these methods, is estimated to be limited to
those of 4-6 mb (megabase) in size.

**FISH Testing**

Molecular cytogenetic testing (aka FISH) may be utilized to address specific,
focused clinical questions and is available for a variety of clinical
application including the assessment of both constitutional and acquired
chromosomal aberrations. FISH testing is a method by which an assessment is
made for the presence, absence, relative position and/or copy number of
specific deoxyribonucleic acid (DNA) segments by fluorescence microscopy. FISH
involves hybridization of a fluorochrome-labeled DNA probe to an in situ
chromosomal target. Metaphase preparations from cultured cells that are
routinely used for cytogenetic analysis are considered the "gold standard"
because morphology and position of the fluorescent signals can be visualized
directly. A major advantage of FISH is that it can be performed on non-
dividing interphase cells, affording a rapid screen for specific chromosome
rearrangements or numerical abnormalities associated with hematologic
malignancies. Interphase analysis can be performed on bone marrow cell
suspensions routinely used for conventional cytogenetics, paraffin-embedded
tissue sections, or disaggregated cells from paraffin blocks, bone marrow,
blood smears and touch-preparations of cells from lymph nodes or solid tumors.  

The majority of probes used for clinical FISH testing are considered analyte-
specific reagents, i.e., reagents that are produced under good manufacturing
practice guidelines set forth by the Federal Drug Administration (FDA), but
their safety and efficacy must be established by the user. When a new analyte-
specific reagent probe is introduced in the lab, specific validation of the
probe itself (probe validation) and validation of the procedures using the
probe (analytical validation) is needed. Known normal and abnormal cases are
used to validate a FISH test. A variety of FISH probes are available:

  * Enumeration probes (e.g., 1 color chromosome 8 -satellite centromere probe; 2 color X/Y probes)
  * Dual-color, dual-fusion probes (e.g., BCR/ABL1; IGH/BCL2; PML/RARA)
  * Single-fusion, extra signal (ES) probes (e.g., ETV6/RUNX1; BCR/ABL1 ES)
  * Break-apart probes (e.g., CBFB, MLL)

Interpretation of the various groups of probes requires significant
experience. Most labs require 2 technologists to score routine FISH
evaluations. For metaphase FISH, it is recommended that clinical FISH tests
include control probes to tag the chromosomes of interest. Such probes provide
a limited level of quality control by providing an internal control of
hybridization efficiency. The interpretation of FISH results should include
consideration of the reason for referral for testing and, when available,
additional laboratory findings including conventional cytogenetic analysis,
histology and immunophenotype.

FISH probes are available for the common chromosomal abnormalities associated
with MDS as FISH panels. Advantages of FISH over standard cytogenetics are:

  * FISH testing can be performed on archived paraffin-embedded clot bone marrow clot sections,
  * Results are available more quickly, and
  * Sensitivity is superior

However, cytogenetics is sufficiently sensitive to detect these abnormalities
in most instances, such that FISH is rarely indicated.

**Diagnostic Report**

The diagnostic report should clearly indicate both the diagnostic and
prognostic significance of the FISH findings. It should also contain a
statement as to the normalcy/abnormalcy of a FISH result, as well as the
percentage of abnormal and normal cells, and whether the results are from
metaphase or interphase cells or from both. Specific naming of the probes used
to obtain results, including the name of the manufacturer, MUST be included in
the written report. Any specific limitations of the assay, some of which may
be described in the probe manufacturer's package insert should be included in
the patient report.

**MDS Testing Algorithm**

Many laboratories adhere to a MDS testing algorithm to determine the necessity
for FISH testing. More than 20 metaphases and a resolved karyotype preclude
FISH testing. Mayo Medical Laboratories (MML) specifies that "MDS FISH does
not increase the detection of MDS if chromosome analysis is successful and >20
metaphases are analyzed."(7) They specify that MDS FISH studies should be
ordered at the discretion of the cytogeneticist if <20 metaphases are
identified, if there is an unresolved karyotype, or if only 1 abnormal
metaphases is indicated. MML also supports use of a FISH study with a specific
probe, but without chromosome analysis for follow-up of a bone marrow for a
previously diagnosed MDS with a specific genetic anomaly.

A number of studies support a MDS testing algorithm that a conventional
karyotype is often all that is needed in the diagnostic process(3,4,5,6,) and
that MDS FISH studies should only be performed when there are fewer than 20
metaphases available for analysis.

The Mayo Clinic has used a diagnostic algorithm in its practice and it
supports this approach. A recent published article by Mayo(7) concludes
"...supports this assumption and showed that MDS-FISH studies provide little
additional value beyond conventional karyotype studies if that study is
adequate (defined by at least 20 metaphases available for analysis)."

The American Society of Clinical Pathology (ASCP) has endorsed this practice
pattern in its practice recommendations in its "Choosing Wisely" program.(8)
The ASCP notes that the added value of MDS FISH on bone marrow is extremely
low when a satisfactory karyotype is obtained (20 interpretable metaphases).
They also note that MDS FISH can be performed post hoc in the event of an
unsatisfactory karyotype.

**Indications and Limitations of Coverage**

****Indications****

FISH testing is indicated in the evaluation of patients whose bone marrow
examination is suggestive of MDS and who have had a failed or inadequate
cytogenetic assessment (conventional karyotype).

**Limitations**

  * When the results of conventional cytogenetics are adequate, FISH testing is not reasonable and necessary and not a Medicare benefit.   
  * When conventional karyotyping is inadequate, Medicare will limit initial FISH testing to 4 probes (studies) as specified above in this policy.
  * Reflex FISH testing may be indicated when the initial 4 probes are negative.
  * Molecular next generation sequencing (NGS) testing alone (for myeloid mutations) or in combination with FISH testing is not reasonable and necessary for the diagnosis of MDS, and is not a Medicare benefit;
  * When a patient has a bone marrow suggestive of another disorder (e.g., a plasma cell disorder), MDS-FISH is not indicated;
  * Delay in diagnosis is not a legitimate reason for performing more than 4 initial FISH studies followed by step-wise reflex testing; 
  * Repeat FISH testing by another laboratory on the same specimen is not reasonable and necessary.

Level of Evidence:

Quality - Moderate to High  
Strength - Moderate  
Weight - Moderate

This Medicare contractor supports the use of conventional karyotyping in
patients being evaluated for MDS and related disorders as being reasonable and
necessary. It is not reasonable and necessary to perform MDS FISH studies when
the conventional karyotype is adequate (20 or more metaphases are available
for analysis), since the evidence suggests that even when FISH does not agree
with conventional karyotyping, it does not meaningfully alter the diagnosis.
When a karyotype is inadequate, FISH testing is limited to up to 4 FISH
studies (+8, -7 or del(7q), -5 or del(5q), and del(20q)). Only when the
initial FISH studies are negative, or there is still diagnostic uncertainty,
will subsequent studies be considered on an individual basis.