The purpose of this test is to assist dermatopathologists to arrive at the
correct diagnosis of melanoma versus non-melanoma when examining skin
biopsies.

This Medicare contractor will provide limited coverage for molecular
Deoxyribonucleic acid (DNA)/Ribonucleic acid (RNA) assays that aid in the
diagnosis or exclusion of melanoma from a biopsy when ALL of the following
clinical conditions are met:

  * The test is ordered by a board-certified or board-eligible dermatopathologist
  * The specimen is a primary (non-metastatic, non-re-excision specimen) cutaneous melanocytic neoplasm for which the diagnosis is equivocal/uncertain (i.e., clear distinction between benign or malignant cannot be achieved using clinical and/or histopathological features alone) despite the performance of standard-of-care test procedures and relevant ancillary tests (i.e., immunohistochemical stains) 
  * The specimen includes an area representative of the lesion or portion of the lesion that is suspicious for malignancy
  * The patient may be subjected to additional intervention, such as re-excision and/or sentinel lymph node biopsy, as a result of the diagnostic uncertainty
  * The patient has not been tested with the same or similar assay for the same clinical lesion
  * The test is validated for use in the intended-use population and is performed according to its stated intended-use 
  * The test demonstrates Analytical and Clinical Validity (AV and CV) and Clinical Utility (CU) and undergoes a technical assessment (TA) by MolDx to demonstrate compliance of the service with this policy

Tests that demonstrate similar indicated uses and equivalent or superior
performance to covered tests may similarly be covered under this policy.

Melanoma is an aggressive cancer with an estimated 106,110 cases and 7,180
deaths in 2021.1 The lifetime risk of developing melanoma in the United States
is approximately 2.6% (1 in 38) for Caucasians, 0.1% (1 in 1,000) for African
Americans, and 0.6% (1 in 167) for Latinos.1 Melanoma is more common in men
overall, but before age 50 the rates are higher in women than in men. The
average age of people diagnosed with melanoma is 65. Many melanomas are
curable if detected early and diagnosed accurately. The five year survival for
localized melanoma is 99%, compared with only 27% among patients with distant
metastases.2

Melanoma can be difficult to diagnose, particularly in its earliest stages,
yet accurate diagnosis of melanocytic neoplasms is vital to optimal patient
outcomes. Histopathologic examination has long been the gold standard for
melanoma diagnosis, and while it is adequate for most cases, evidence suggests
that approximately 15-20% of all biopsied melanocytic neoplasms are difficult
to diagnose by histopathology alone.3-5 Subspecialty training and experience
in dermatopathology is associated with improved diagnostic accuracy and
subsequent clinical management of patients with challenging melanocytic
lesions.5-8 However, even experienced dermatopathologists disagree in some
cases, and, depending on the type of lesions evaluated, diagnostic discordance
may be substantial.6,7,9,10 In equivocal cases, patients may receive diagnoses
that are indeterminate or inaccurate, leading to inappropriate treatment.
Unnecessary re-excisions, sentinel lymph node biopsies, and protracted
clinical follow-up may result when a diagnostically challenging benign lesion
is reported as indeterminate.11,12 Conversely, a diagnostically challenging
melanoma mistakenly classified as a benign nevus may result in undertreatment
and subsequent progression to late-stage melanoma.11,12 Consequently, adjuncts
to histopathology have been sought in efforts to improve diagnostic accuracy
in equivocal cases.

Gene expression profiles (GEP) can serve as beneficial adjuncts to
histopathology in the evaluation of equivocal melanocytic lesions. The myPath
Melanoma assay (Castle Biosciences, Phoenix, AZ) is a 23-gene expression
profile (23-GEP) developed to provide an objective, reproducible, and accurate
adjunctive method for differentiating malignant melanoma from benign
nevi.13-16 The test is intended for use by dermatopathologists confronting
primary cutaneous melanocytic neoplasms for which the diagnosis of malignant
melanoma versus benign nevus is equivocal/uncertain (i.e., a clear distinction
between benign or malignant cannot be achieved using clinical and/or
histopathological features alone). Use of the test in these cases increases
definitive diagnoses, and evidence suggests it may reduce unnecessary
procedures in benign lesions.17,18

The myPath Melanoma test quantifies the expression of 23 genes by
quantitative reverse transcription-polymerase chain reaction (RT-PCR).
Fourteen of the 23 genes are known to be over-expressed by malignant melanomas
relative to benign nevi. The remaining 9 are stably expressed reference genes
which allow correction for sample-to-sample variations in RT-PCR efficiency
and errors in sample quantification (normalization). The signature genes
represent 3 distinct pathways that contribute to melanoma pathogenesis,
including aspects of melanocyte differentiation as well as characteristics of
the tumor microenvironment such as cell-cell signaling and tumor-induced host
immune responses.13,14 The test uses 5 to 7 standard-thickness (4-5 m)
sections taken from the routinely processed formalin-fixed paraffin-embedded
(FFPE) tissue of the existing biopsy specimen, allowing its integration into
routine clinical practice and its use even in small, early-stage lesions. The
quantified expression of all 23 genes is combined algorithmically and reported
as a single numerical score. That number (the myPath Melanoma 'score'), is
plotted on a scale that depicts the entire range of scores observed in
clinical validation studies.14 Physicians receive a report showing this single
numerical score and the corresponding classification: 'likely malignant',
'likely benign', or 'indeterminate'.

Histopathology can accurately classify many melanocytic neoplasms and
currently serves as the 'gold' standard for the diagnosis of melanoma. In line
with standard practice, therefore, adjunctive molecular tests for melanoma
diagnosis have largely been developed and initially evaluated using
histopathology as the reference standard. The first 2 validation studies of
the myPath Melanoma test demonstrated greater than 90% diagnostic accuracy by
comparison to concordant histopathologic diagnoses (diagnoses arrived at
independently by multiple expert dermatopathologists).14,15 To further assess
accuracy using a reference standard independent of histopathologic diagnosis
and confirm genuine clinical utility, a third clinical validation study was
performed in which the test result was compared to the eventual clinical
outcomes of tested patients.16 In a cohort of 182 melanocytic neoplasms
collected from patients with documented outcomes (distant metastases for
malignant melanomas and median 6+ year uneventful follow-up for benign nevi),
the myPath Melanoma score differentiated malignant melanoma from benign nevi
with a sensitivity of 93.8% and a specificity of 96.2%.16 Overall, clinical
studies have shown sensitivity and specificity ranges of 90-94% and 91-96%,
respectively, for the 23-GEP.14-16,19

A clinical utility study quantified the influence of the myPath Melanoma
score on both the final diagnoses and the treatment recommendations made by
board-certified dermatopathologists for 218 prospectively submitted
diagnostically challenging (equivocal or uncertain) melanocytic neoplasms
encountered during routine clinical practice. Comparison of pre-test and post-
test diagnoses demonstrated a 56% increase in definitive diagnoses with use of
the myPath score (a 30% increase in definitive diagnoses of benign nevus and
a 12.4% increase in definitive diagnoses of malignant melanoma).17 In
addition, treatment recommendations provided by dermatopathologists changed
for 49% of patients after receiving the myPath result, with 76.6% of those
changes aligned to the test result.17 A second clinical utility study assessed
the relationship between test result and change in treatment as measured by
pre-test dermatopathologist recommendation and post-test actual treatment
delivered to a patient by the dermatologist. A cohort of 77 patients with pre-
test diagnoses of "indeterminate" (equivocal, uncertain) were followed
throughout their clinical course. The myPath test produced definitive scores
for all 77 neoplasms, and after a median 12-month follow-up period, the tested
patients' dermatologists disclosed the actual treatment carried out in each
case.18 The treatment differed from the pre-test recommendation in 55 of 77
(71.4%) cases, 44 of which produced a benign myPath test result. Re-excision
was the pre-test treatment recommendation for 41 of these 44 cases, yet re-
excision was ultimately performed in just 7, indicating that a benign myPath
test result enabled dermatologists to forego further intervention in 33 of the
41 cases, yielding an 80.5% reduction in re-excisions.18

DecisionDx DiffDxTM-Melanoma (DiffDxTM-Melanoma), also by Castle Biosciences,
is a 35-gene expression profile (35-GEP) performed on FFPE tissue that is
intended to discern benign from malignant melanocytic lesions. It is based on
the RT-PCR quantified expression of 32 discriminant and 3 reference genes. The
quantified expression of all 35 genes is combined algorithmically and results
in two signatures denoting one of three possible risk groups: 'benign,'
'intermediate,' or 'malignant.'

The training and validation cohorts included a total of 951 samples diagnosed
between January 2013 and August 2020, of which 498 were benign and 453
malignant. Clinical Validation was performed in 273 benign and 230 malignant
lesions (inclusive of a variety of subtypes), with six dermatopathologists
performing the review of cases for diagnostic concordance.20 Overall, 96.4% of
cases received a definitive benign or malignant test result and 3.6% had
intermediate-risk, exceeding performance of currently available ancillary
diagnostic tools including the myPath Melanoma test, which classifies up to
15% of challenging melanocytic lesions as indeterminate.15,20,21 After
exclusion of lesions identified as intermediate-risk, the test demonstrated a
sensitivity of 99.1%, specificity of 94.3%, positive predictive value of 93.6%
and negative predictive value of 99.2%.20 A multi-center clinical utility
study found that use of the 35-GEP test resulted in a change of diagnosis in
41.7% of cases, including diagnostic downgrades in 20.3% and upgrades in 21.4%
of diagnostically challenging melanocytic lesion cases.22 The study also
reported a 76.7% decrease in re-excisions in cases with benign 35-GEP
results.22

Other diagnostic adjuncts for melanocytic neoplasms include
immunohistochemistry (IHC) to detect expression of the melanoma-associated
antigen PRAME (Preferentially Expressed Antigen in Melanoma) as well as tests
that rely upon the detection of chromosomal aberrations within neoplastic
melanocytes (tumor cytogenetics), such as fluorescence in situ hybridization
(FISH)23-28 and array comparative genomic hybridization (aCGH)/single
nucleotide polymorphism (SNP) array.23,29-32

Diffuse immunoreactivity for PRAME is found in most primary cutaneous (and
ocular) melanomas, whereas most melanocytic nevi either do not express PRAME
or express it only in a subpopulation of cells.33 As such, it can be a useful
and lower-cost adjunct for the diagnosis of challenging melanocytic lesions.
However, up to 14% of benign melanocytic nevi show some immunoreactivity for
PRAME;33 additionally, the interpretation of positive staining can be
subjective. Moreover, though it is highly concordant with FISH, its reported
sensitivity is lower than that of the GEP assays, ranging from 75-85% across
studies.20,33,34 PRAME is also a component of the myPath Melanoma assay15,16
and is one of the two genes used in a pre-biopsy assay to help guide
clinicians on the need for biopsy of a melanocytic lesion.35

FISH queries 4 to 6 chromosomal loci through hybridization of fluorescent
probes. Tissue requirements are minimal (25-35 m),23 and since FISH involves
visualization of the tissue, aberrations may be detected within tumor cell
subpopulations. Melanomas lacking aberrations at the 4-6 target loci will be
undetected, however, generating false negative results,24-28 while polyploidy
may produce false positives27,28 (but may be detected by experienced
observers). Results are uninterpretable (e.g., insufficient signal) in 5-30%
of cases.24-26 Probe sets, cut-off thresholds, and observer skill and
experience vary among laboratories, and inter-observer variability
occurs.27,28,32

In contrast to FISH, SNP array/aCGH methodologies interrogate the genome more
broadly29-32 and signal quantification does not involve human interpretation.
However, tumors must be relatively homogenous (~40%),31 meaning that
aberrations in cell subpopulations may go undetected. The large quantity of
tissue required (125-375 m / 10 mm2)23 restricts use to thicker tumors, and
the significance of some aberrations remains unknown.

By comparison to the cytogenetic techniques, the GEP tests quantify the (RNA)
transcripts produced by genes over-expressed in malignant melanoma.13-16 Human
interpretation is not involved, maximizing objectivity and reproducibility.13
Testing is performed in a single laboratory, reducing variation in methods and
reagents, and tissue requirements are minimal.13,20 However, testing requires
an area in which neoplastic melanocytes represent approximately 10% of the
specimen,13-15,20 and a proportion of scores are classified as indeterminate
(3.6-15% of tested cases).20,21 The myPath Melanoma and DiffDxTM-Melanoma
assays are only validated for primary cutaneous neoplasms, precluding testing
of metastases, non-cutaneous melanomas, and re-excision specimens.13-16,20





Studies demonstrate that Medicare beneficiaries with diagnostically
challenging primary cutaneous melanocytic lesions tested with ancillary
diagnostic tests (such as GEPs) will have improved outcomes, as defined by an
increase in accurate diagnoses, appropriate clinical management and
interventions, and a reduction in burdensome and unnecessary
treatments.17,18,20,22

The National Comprehensive Cancer Network (NCCN) Guidelines also support
ancillary diagnostic testing (including with GEPs) to better classify
melanocytic neoplasms of uncertain diagnostic potential. As noted in the
guidelines, "Ancillary tests to differentiate benign from malignant
melanocytic neoplasms include immunohistochemistry (IHC) and molecular testing
via comprehensive genomic hybridization (CGH), fluorescence in situ
hybridization (FISH), gene expression profiling (GEP), single-nucleotide
polymorphism (SNP) array, and Next-Generation Sequencing (NGS). These tests
may facilitate a more definitive diagnosis and guide therapy in cases that are
diagnostically uncertain or controversial by histopathology."36 The guidelines
further recommend that ancillary tests should be used as adjuncts to clinical
and expert dermatopathologic examination and consultation and therefore need
to be interpreted within the context of these findings.36

Each test has benefits and limitations, as noted in the Summary of Evidence.
As such, dermatopathologists can choose the test that best suits the patient's
needs, according to the criteria outlined in this policy.

The reference to specific tests in this document does not imply coverage by
MolDX. Further, this policy is restricted in scope to molecular (DNA)/RNA
tests only; therefore, non-molecular tests for the same intended use, though
not covered by this policy, may meet coverage criteria of other local coverage
determinations.

This contractor will continue to monitor the evidence and coverage may be re-
evaluated following any substantial new evidentiary developments or guideline
changes.