This is a limited coverage policy for assays that detect biomarkers from
circulating tumor cells (CTCs).

**Criteria for Coverage**

_Cancers with established biomarker testing, as recommended by society or
national guidelines_

Assays that detect biomarkers from CTCs are covered when ALL of the following
are met:

  * The patient has been diagnosed with cancer
  * The specific cancer type has an associated biomarker 
  * The associated biomarker has already established clinical utility (CU) in the peer-reviewed published literature for the intended cancer type and for the specific indication in the intended patient population 
    * The biomarker's CU may include any of the following: it can be used to diagnose, risk-stratify, predict, or monitor response to therapy, as recommended by national or society guidelines (i.e., American Society of Clinical Oncology (ASCO), National Comprehensive Cancer Network (NCCN))
  * At least 1 of the following criteria are met AND there is clear documentation of at least 1 of these in the medical record: 
    * The patient's cancer has not previously been tested for the specific biomarker, **OR**
    * The patient has newly metastatic cancer, and a metastatic lesion has not been tested for the specific biomarker, **OR**
    * The patient demonstrates signs of clinical, radiological or pathologic disease progression, **OR**
    * There is concern for resistance to treatment based on specific and well-established clinical indications
  * Testing for the biomarker can be performed using CTCs
  * The CTC-based biomarker test successfully completes a comprehensive Technical Assessment (TA) by Molecular Diagnostic Services Program (MolDX) that will ensure that Analytical Validity (AV) (including an analytical and clinical validation), Clinical Validity (CV), and CU criteria are met to establish the test as Reasonable and Necessary.
    * The clinical validation has demonstrated performance that is equivalent or superior to tissue-based testing or another already-accepted test for the same biomarker for the same intended use.
    * CV (for new analytes) must be established through studies published in the peer-reviewed literature for the intended use of the test in the intended population.
  * Tissue-based testing for the specific biomarker is infeasible (e.g., quantity not sufficient or invasive biopsy is medically contraindicated) **OR** will not provide sufficient information for subsequent medical management (e.g., in cases where human epidermal growth factor receptor 2 (HER2) overexpression is negative in a tissue biopsy but may be positive in the CTCs, due to tumor heterogeneity). There is clear documentation of at least 1 of these reasons for testing in the medical record.
  * For a given patient encounter, only 1 test for assessing the biomarker may be performed UNLESS a second test, meeting all the criteria established herein, is reasonable and necessary as an adjunct to the first test.
  * Duplicate testing of the same biomarker ( _from the same sample type and for the same clinical indication_ ) using different methodologies is not covered. For example, testing for androgen receptor splice variant 7 (AR-V7) from CTCs by messenger RNA (mRNA) as well as immunohistochemistry (IHC)-based methodologies, for the same clinical indication, will not be covered.

Testing for biomarkers in cancer is often a routine part of medical care.1
Biomarker testing can be performed from tissue samples, or from samples
obtained using less-invasive means such as the liquid biopsy. In the liquid
biopsy approach, testing is performed on cancer-derived components (including
CTCs) found in peripheral blood or other body fluids.2 Specifically, the
testing of CTCs in liquid biopsy specimens involves cell capture, enrichment,
and downstream molecular characterization, with the goal of impacting disease
management in cancer.3 Current technological approaches for identifying
biomarkers from CTCs include distinguishing the comparatively rare tumor cells
from among the large number of normal cells by image processing and/or direct
capture techniques, along with staining for the biomarker of interest.4-7

CTCs can be used to detect biomarkers important for prognosis, identifying
treatment, and monitoring response to treatments in cancer. Biomarker
detection from CTCs may therefore serve as a potential alternative to
biomarker detection from biopsy specimens for certain cancers, including
breast and prostate.4-7

**_Breast Cancer_**

In 1998 the Food and Drug Administration (FDA) approved the drug Herceptin
(trastuzumab) for the treatment of HER2 over-expressing breast cancer. Testing
for HER2 has become 1 of the most important sources of information in making
management decisions regarding systemic therapy in breast cancer. The NCCN
guidelines on breast cancer recommend that all patients who have new primary
or newly metastatic breast cancers be tested for HER2 using a methodology
outlined in the ASCO/College of American Pathologists (CAP) guideline.8,9
Traditionally, testing for HER2 was performed using tissue. Testing from
tissue, however, can be associated with complications. For example, breast
malignancies may metastasize to the brain,10 and analyses of complications
following brain biopsies have shown a wide array of complications ranging from
neurologic complications to general surgical complications.11,12

Studies have demonstrated that it is feasible to collect CTCs from breast
cancer and to identify the HER2 biomarker in the circulating cells, achieving
results that are concordant with tissue HER2 testing.4,5 Additional studies
have examined whether patients with HER2 negative tissue but HER2 positive
CTCs respond to trastuzumab, and have shown minimal effect of this therapy in
such patients.13,14 Conversely, research has shown that patients with HER2
positive tissue in early breast cancer may have HER2 negative CTCs, and it is
posited that this may contribute to drug resistance.15 Interest persists with
other studies ongoing to evaluate the use of HER2 positive CTCs to help guide
treatment.16

**_Prostate Cancer_**

The androgen receptor (AR) is 1 of the most important pathways in prostate
cancer. It is involved in disease progression and resistance to treatment. For
these reasons, it is a common target of hormone-based therapies, including
androgen deprivation therapy. AR-V7 is an AR splice variant that results in
constitutive activation of oncogenic signaling and cell proliferation and has
been implicated in resistance to androgen receptor signaling (ARS)
inhibitors.17-19 Prospective multicenter studies in men with metastatic
castration-resistant prostate cancer (mCRPC) have shown that detection of
AR-V7 in CTCs is associated with resistance to the ARS inhibitors enzalutamide
and abiraterone, whereas in AR-V7-negative patients, the taxanes and ARS
inhibitors show comparable efficacy.6,20,21 Additionally, AR-V7 status may
change during therapy.22 For these reasons, NCCN guidelines recommend AR-V7
testing in CTCs to help guide selection of therapy after progression on
abiraterone or enzalutamide in mCRPC.23

**_CTC-associated Biomarkers in Other Cancers_**

HER2 is overexpressed in malignancies other than breast cancer.24
Overexpression of HER2 on cancer cells has been reported in 10%-26% of gastric
and esophagogastric junction cancers, particularly in cancers with intestinal-
type histology.25-27 In gastric cancer, HER2 has been established as a
predictive biomarker for HER2-targeted therapies, and in HER2 overexpressed
metastatic gastric adenocarcinoma, trastuzumab is now recommended to be added
to first-line chemotherapy.28 Additional trastuzumab-based therapies such as
Enhertu (fam-trastuzumab deruxtecan-nxki) have also been approved for the
treatment of adults with locally advanced or metastatic HER2 positive gastric
or gastroesophageal junction (GEJ) adenocarcinoma who have received a prior
trastuzumab-based regimen.29,30 HER2 is also amplified in approximately 3% of
colon cancers, and in 5%-14% of Rat sarcoma viral oncogene homolog (RAS)/
B-Raf murine sarcoma viral oncogene homolog B1 (BRAF)-wild type tumors.31,32
In colon cancer, HER2 overexpression may have a role in predicting response to
HER2 targeted therapies and resistance to epidermal growth factor receptor
(EGFR)-specific therapies, and anti-HER2 combination therapies have shown
promise in HER2 overexpressing, RAS/RAF-wild type, metastatic colorectal
cancers (mCRC).31-37 In gastric cancer, studies have shown conflicting levels
of concordance of HER2 copy number between tissue and plasma samples.25,38-40
As with breast and other solid tumors, discordance is reported and thought to
be, at least in part, due to tumor heterogeneity.39,40 One study reported
HER2-overexpressed CTCs in up to approximately 32% of all recurrent or
metastatic gastrointestinal cancer patients; this same study observed a HER2
discordance rate of 35.5% between tumor cells and CTCs.39 Though liquid biopsy
holds promise, to-date NCCN guidelines recommend that methods for HER2 testing
in gastric cancer remain IHC and fluorescence in situ hybridization (FISH), or
another in situ hybridization (ISH) method, with next-generation sequencing
(NGS) being acceptable when there is limited tissue and sequential biomarker
testing is infeasible.28,41,42 Similarly, for colorectal cancer, NCCN
guidelines recommend HER2 and other biomarker testing in mCRC by IHC, FISH, or
NGS.43

In non-small cell lung cancer (NSCLC), NCCN guidelines state that cell-
free/circulating tumor DNA (ctDNA) may be used for molecular analysis of the
EGFR and anaplastic lymphoma kinase (ALK) genes, as well as other oncogenic
biomarkers if tissue is insufficient for testing or if the patient is
medically unfit for invasive tissue sampling.44 Detection of these biomarkers
has also been achieved using CTCs; moreover, analysis at disease progression
has detected new mutations in EGFR (including the T790M mutation, which
confers drug resistance).45 However, studies have reported that ctDNA has
shown greater sensitivity than CTCs for detecting mutations in EGFR and the
Kirsten rat sarcoma virus oncogene (KRAS), when compared with mutation status
in matched tumor.46,47 CTCs can also detect clinically significant genetic
rearrangements in NSCLC.48,49 In 1 study using filter-adapted FISH, variations
in ALK-rearranged CTC levels were observed during treatment with crizotinib.48
In another study, an increase of ROS1-rearranged CTCs was associated with
resistance to crizotinib.49 Overall, biomarker testing from CTCs in lung
cancer remains a promising and active area of investigation.

**_CTC Enumeration_**

The detection of CTCs has been evaluated in localized as well as in metastatic
cancers, and CTCs have potential utility beyond that of their molecular
characteristics (biomarkers). For example, CTC enumeration and variation over
time can serve as indicators of cancer detection, prognosis, recurrence, and
treatment response in a variety of cancers.50,51 CTC counts have been shown to
change after treatment in patients with metastatic breast (mBC), colorectal
(mCRC), and prostate (mPC) cancers, and prognostic information may be obtained
by the serial monitoring of patients.52 In breast cancer, numerous studies
have shown enumeration of CTCs to be a good prognostic marker and measure of
treatment response,53-57 though these studies do not suggest a clear effect on
outcomes from a change in treatment.9,58 The STIC CTC Randomized Clinical
Trial showed that CTC enumeration may be useful in guiding the choice between
chemotherapy and endocrine therapy as a first-line treatment in hormone
receptor-positive, HER2-negative metastatic breast cancer.59 However, in a
prospective randomized trial (SWOG S0500), serial enumeration of CTC in
patients with metastatic breast cancer and switching to alternate cytotoxic
therapy (in patients with persistently high CTCs) did not affect progression-
free survival (PFS) or overall survival (OS).58 For these reasons, the
enumeration of CTCs in metastatic breast cancer is not yet included in the
NCCN guidelines for assessment and monitoring.9 Moreover, in prostate cancer,
a 30% decline in CTCs (approximately 1 month after treatment initiation) was
shown to distinguish between patients benefiting and those not benefiting from
treatment; in the latter group, those patients might be considered for a
change in therapy.60 Though in metastatic prostate cancer CTC enumeration has
been shown to provide good prognostic information,61-64 in localized prostate
cancer, the same methodology may underestimate the actual number of CTCs.65
Limitations of CTC enumeration include low rates of detection (depending on
the particular cancer type and severity), differences in the sampling and
testing methods used, and the lack of standardization of cut-offs and time-
points for assessment.51 CTC enumeration may be a good prognostic indicator
for certain cancers, but studies do not conclusively suggest a clear effect on
outcomes resulting from a change in management.

Numerous prior Medicare coverage decisions have considered the evidence in the
hierarchical framework of Fryback and Thornbury66 where Level 2 addresses
diagnostic accuracy, sensitivity, and specificity of the test; Level 3 focuses
on whether the information produces change in the physician's diagnostic
thinking; Level 4 concerns the effect on the patient management plan and Level
5 measures the effect of the diagnostic information on patient outcomes. To
apply this same hierarchical framework to analyze an in vitro diagnostic test,
we utilized the ACCE Model Process for Evaluating Genetic Tests.67 The
practical value of a diagnostic test can only be assessed by taking into
account subsequent health outcomes. When a proven, well established
association or pathway is available, intermediate health outcomes may also be
considered. For example, if a particular diagnostic test result can be shown
to change patient management and other evidence has demonstrated that those
patient management changes improve health outcomes, then those separate
sources of evidence may be sufficient to demonstrate positive health outcomes
from the diagnostic test.

Biomarker detection is often the standard of care in cancer, and is included
in various cancer-specific guidelines, as well as in the NCCN Biomarkers
Compendium.1 Biomarker detection from non-invasive (liquid) specimens are
becoming increasingly important in the diagnosis, management, and treatment of
cancer, as tissue can be difficult to obtain or may not be available. The
detection of biomarkers from CTCs has shown promise in various cancer
types.2,68 However, not all clinically relevant biomarkers are reliably
detected from CTCs. Therefore, the CU of CTC-based biomarker detection is
limited to specific cancer-biomarker combinations.

The evidence to-date supports HER2 testing from CTCs in breast cancer and
AR-V7 testing from CTCs in prostate cancer.4-7 The presence of HER2
overexpression in breast cancer is currently the basis for making treatment
decisions (regarding HER2 and anti-HER2 therapy) in well-accepted guidelines.9
Existing evidence, however, does not suggest that the presence of HER2
positive CTCs by itself can be interpreted in the same manner as HER2 positive
tissue. Whether this is related to technical matters related to the assays or
different clinical significance for CTCs as compared with tissue is unclear.
However, assays of CTCs can be developed to provide results that are
concordant with tissue HER2 results. In prostate cancer, the presence of AR-V7
from CTCs is currently the basis for making treatment decisions regarding
taxane versus ARS inhibitor therapy and is recommended by NCCN guidelines.23

As the field evolves, it is likely that additional clinically relevant
biomarkers will be reliably detected from CTCs. The use of CTCs may emerge as
a viable alternative method for HER2 testing in other cancer types for which
HER2 has demonstrated CU, such as gastroesophageal and colorectal
cancers.28,43,68 CTC-based biomarker testing is also likely to include
mutations and gene-rearrangements in NSCLC.45,48,49 This contractor will
consider coverage for tests that use CTCs to accurately and reliably identify
biomarkers with established CU in cancer. Finally, though CTC enumeration may
be a good prognostic indicator for certain cancers, the evidence does not
conclusively suggest a clear effect on outcomes resulting from a change in
management.3,9,51 Therefore, coverage is restricted to tests that detect
biomarkers from CTCs (regardless of whether they also enumerate CTCs).

Given that there are ongoing studies on the use of CTCs (including
enumeration) and the detection of biomarkers from CTCs in various cancer
types, this contractor will continue to monitor the evidence and may modify
coverage as needed.