This Medicare contractor will provide limited coverage for minimally invasive
molecular deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) tests that
detect minimal residual disease (MRD) in patients with a personal history of
cancer.

This Contractor provides limited coverage for MRD testing in cancer when ALL
of the following are true:

  1. If Next-Generation Sequencing (NGS) methodology is used in testing, the conditions set by NCD 90.2 are fulfilled (summarized: the patient has advanced cancer; plans on being treated for said cancer, and has not been previously tested with the same test for the same genetic content) or are not applicable (the patient does not have cancer as defined below);
  2. The patient has a personal history of cancer, the type and staging of which is within the intended use of the MRD test;
  3. The identification of recurrence or progression of disease within the intended use population of the test is identified in the National Comprehensive Cancer Network (NCCN) or other established guidelines as a condition that requires a definitive change in patient management;
  4. The test is demonstrated to identify molecular recurrence or progression before there is clinical, biological or radiographical evidence of recurrence or progression AND demonstrates sensitivity and specificity of subsequent recurrence or progression comparable with or superior to radiographical or other evidence (as per the standard-of-care for monitoring a given cancer type) of recurrence or progression;
  5. To be reasonable and necessary, it must also be medically acceptable that the test being utilized precludes other surveillance or monitoring tests intended to provide the same or similar information, unless they either (a) are required to follow-up or confirm the findings of this test or (b) are medically required for further assessment and management of the patient;
  6. If the test is to be used for monitoring a specific therapeutic response, it must demonstrate the clinical validity of its results in published literature for the explicit management or therapy indication (allowing for the use of different drugs within the same therapeutic class, so long as they are considered 'equivalent and interchangeable' _for the purpose of MRD testing_ , as determined by national or society guidelines);
  7. Clinical validity (CV) of any analytes (or expression profiles) measured must be established through a study published in the peer-reviewed literature for the intended use of the test in the intended population; 
  8. The test is being used (a) in a patient who is part of the population in which the test was analytically validated and (b) according to the intended use of the test;
  9. The MRD test [unless it is a Food and Drug Administration (FDA) approved and established standard-of-care single-gene polymerase chain reaction (PCR)] satisfactorily completes a technical assessment (TA) that will evaluate and confirm that the analytical validity, clinical validity, and clinical utility criteria set in this policy are met to establish the test as Reasonable and Necessary; 
  10. Tests utilizing a similar methodology or evaluating a similar molecular analyte to a test for which there is a generally accepted testing standard or for which existing coverage exists must demonstrate equivalent or superior test performance (i.e., sensitivity and/or specificity) when used for the same indication in the same intended-use population.

MRD testing often requires 2 types of assays to be performed as part of the
service. First, a sample is taken from tumor diagnostic material to establish
a baseline (solid and/or liquid) tumor signature as defined by the test
methodology. This is followed by a series of assays run on a minimally
invasive specimen (i.e., liquid biopsy or bone marrow aspirate)  to detect the
presence or recurrence of tumor, based on the measured biomarkers, expression,
or other analytes over various timepoints. Other approaches are also
acceptable, based on the validity established for the individual test
comprising the service. This series of assays comprises a single test when the
patient is known to have cancer.

When the patient is NOT known to have cancer (specifically when there is no
clinical, radiographical, or other biological evidence that tumor cells remain
post treatment and subsequently the patient is no longer being subjected to
therapeutic interventions for cancer), a second kind of test may exist wherein
a single timepoint may constitute a single test. In such patients, the
frequency of MRD testing is in accordance with national or society guidelines
or recommendations.

For patients with or without cancer (as defined above), established standard-
of-care MRD tests using single-gene PCR (i.e., BCR-ABL1) are covered under
this policy according to testing schedules outlined in national (i.e., NCCN)
or society guidelines.

MRD testing in accordance with this policy can be performed using PCR and/or
sequencing-based technologies and is not restricted to a single type of
biological material or defined number of genes.

**_Background_**

MRD testing for cancer is rapidly becoming a sensitive and specific method for
monitoring the relative amounts of tumor-derived genetic material circulating
in the blood of cancer patients. These tests leverage new genomic technologies
that allow detection of extremely dilute tumor material, yielding an extremely
sensitive method for determining the continued presence of tumor material or,
by serially testing the same individual, tracking the relative increase or
decrease of tumor material being deposited in the blood. Although it is a
relatively new application of novel genomic technologies, it has rapidly
demonstrated its ability to impact patient care in several ways in cancer
diagnosis and treatment. MRD testing can be used to:

  * diagnose cancer progression, recurrence, or relapse before there is clinical, biological, or radiographical evidence of progression, recurrence or relapse
  * detect tumor response to therapy by measuring the proportional changes in the amount of available tumor DNA

Both above uses may enable physicians to better assign risk stratification,
deploy alternate treatment strategies, or preclude the use of unnecessary
adjuvant therapies.

**Examples of current uses:**

**__**

**_Colorectal Cancer and Solid Tumors_**

Colorectal cancer (CRC) is the second leading cause of cancer-related
mortality, with an estimated 145,600 newly diagnosed cases in the United
States (U.S.)1 The current standard of care for patients with localized or
regionally advanced CRC involves surgical resection, possibly followed by
adjuvant radiation or adjuvant chemotherapy (ACT).2,3 It is generally accepted
that earlier recurrences are more likely to be treated with curative intent
and that these patients have improved overall survival after such
interventions.4 Existing consensus guidelines for the treatment of colon
cancer recommend surgical resection as a key treatment for Stage II cancer
with the consideration of adjuvant chemotherapy, but notes that patients
should be counseled that the absolute benefit is not more than 5% in colon
cancer.2 The evidentiary review that appears to underlie the recommendation in
colon cancer is based on a number of studies, among them a meta-analysis by
Bockelman, et al.5

The NCCN's colon cancer guideline reviews these findings in addition to a
number of other studies and concludes that for patients with average risk
stage II colorectal cancer the benefit of adjuvant therapy is small, and
patients with high risk features have been considered more likely to benefit
from adjuvant chemotherapy, although data is lacking. Uniform patient
stratification based on risk features is lacking, resulting in physician
discretion likely being a major factor in ACT use. In NCCN guideline
concerning rectal cancer, ACT vs observation is the recommend treatment for
pT3N0M0 tumors.3 Current surveillance methods in CRC include history taking
and physical exams, periodic chest/pelvic imaging, colonoscopies, and serial
carcinoembryonic antigen (CEA) monitoring at intervals dependent on patient
stage. Serial CEA elevations result in a suspicion of recurrence, resulting in
a subsequent workup.

MRD testing may be beneficial for patients in that it may be a more sensitive
and specific method for detecting or predicting recurrent disease than current
surveillance methods; furthermore, it may help risk-stratify patients that may
or may not benefit from ACT because although they may not have radiographical
evidence of disease, they may have residual microscopic tumor detected at the
molecular level that may require additional ACT treatment. Multiple studies
have to date been performed to evaluate these scenarios.

One commercial MRD test was evaluated in a prospective, multicenter cohort
study of 125 patients with stages I-III CRC.6 Testing was performed pre-
operatively, post-operatively, and in longitudinal follow-up. The mean age of
the 130 patients enrolled (the data from 5 were not analyzed) was 67.9 years.
Pre-operative testing showed that baseline disease detection of circulating
tumor DNA (ctDNA) when compared with CEA (a current method for disease
surveillance in CRC) was 88.5% vs. 43.3%. In the post-operative setting,
immediately before and after ACT treatment, MRD-positive patients had hazard
ratios (HR) for relapse of 7.2 (P<0.001) and 17.5 (P<0.001), respectively,
when compared to MRD-negative patients. The study also demonstrated that
repeat sampling increases the sensitivity of the test. Of the patients who had
recurrence, the test had a sensitivity of 87.5% for relapses at or before the
time of radiographic detection. In the post-surgical period, a positive test
result without additional treatment was followed by relapse in over 98% of
cases. With treatment, 30% of MRD-positive patients cleared their ctDNA and
remained MRD-negative and disease free throughout the follow-up period. In
contrast, longitudinal CEA analysis identified relapse with a sensitivity of
69% and a specificity of 64%, with no lead time when compared with radiologic
imaging. The study determined that MRD status was the only factor
significantly associated with relapse-free survival, after adjusting for all
other standard clinicopathological factors.

At the same time that the above paper was published, another publication on
the use of MRD testing in ctDNA demonstrated in a similar population that MRD
could identify molecular recurrence/predict recurrence with similar
sensitivity and specificity with a 4-month lead time.7 In this study, patients
that did not show evidence of MRD similarly did not have recurrence regardless
of ACT use.

An editorial8 was published with these 2 studies that remarked:

_Based on findings from these 2 case series, ctDNA assays can be used to
classify recurrence risk for patients with nonmetastatic CRC after standard-
of-care treatment, and perhaps may be better than the commonly used clinical,
laboratory, and pathological risk factors in this setting. Likewise, ctDNA
assays may identify patients with early-stage CRC and no detectable residual
tumor DNA who may be suitable for de-escalation approaches, given their
associated favorable prognosis._

_Subject Matter Expert Input_

Samuel Jacobs and Carmen Allegra, directors of Medical affairs at the National
Surgical Adjuvant Breast and Bowel Project expressed support for clinical use
of ctDNA, particularly in post-surgical setting for the treatment of colon
cancer. They referenced the recent paper6and indicated that the information
provided by ctDNA testing to look for micrometastatic disease will "more
clearly inform physician-patient decision making." They also indicated that
they are working on a protocol to utilize ctDNA assessment after the
completion of adjuvant therapy to identify patients who may benefit from
additional therapy.

Scott Kopetz, Associate Professor and Deputy Chair for Translational Research
in the Department of Gastrointestinal Medical Oncology at M.D. Anderson Cancer
center submitted a letter supporting the use of ctDNA MRD testing for local
and regionally advanced colorectal cancer given the published data, especially
where such results are felt to be useful in guiding adjuvant treatment
decision. Dr. Kopetz noted: _The clinical utility of Signatera_ [a commercial
ctDNA test] _is supported by several studies that successfully utilize the
test for a range of applications including post-surgical risk stratification,
therapy monitoring, and early relapse detection in different solid tumors._

Jason B. Fleming, chair of the Department of Gastrointestinal Oncology at
Moffitt Cancer Center provided insightful commentary about the ways in which
CRC is treated and how molecular residual disease testing relates to that
paradigm. He indicated that the decision to use ACT is driven by consensus
using prognostic factors, but that these broad recommendations often fail when
applied to an individual patient. He noted that disease recurrence is thought
to arise from micrometastatic disease, and clinicopathologic prognostic
factors provide probabilistic expectations about the existence of
micrometastatic disease; these expectations serve as a basis for risk
stratification for treatment decisions. The advance that MRD testing brings is
that rather than being a probabilistic estimate, this test directly measures
the presence of micrometastatic disease. As such, ctDNA assessment can help
improve adjuvant clinical decision making within existing practice guidelines.
He also discussed surveillance for disease recurrence in patients who have had
CRC, noting that this relies on CEA measurement and imaging studies. Detection
of asymptomatic recurrence can lead to potentially curative surgery for
oligometastatic disease, but these conventional surveillance techniques miss
many patients and have poor specificity. As such, the data suggests that MRD
testing, which can identify recurrence up to 16 months earlier with an
"extremely high specificity of 98%," can safely replace CEA monitoring in
patients undergoing surveillance. He concluded by explicitly stating his
belief that there is sufficient evidence to recommend ctDNA based MRD
assessment when "(1) improved risk stratification will be helpful for adjuvant
chemotherapy decisions for patients with local and regionally advanced CRC and
(2) surveillance for recurrence where patients would be candidates for further
surgical treatment for oligometastatic disease."

**_MRD in other solid tumor types:_**

In addition to CRC, MRD testing has been performed in multiple cancer types.
Validation studies for the use of MRD testing have been conducted in lung
cancer, breast cancer, bladder cancer, and esophageal cancer, among
others.9-12 MRD testing across multiple cancer types demonstrates consistent
sensitivity and specificity (ranging from 88-100% sensitivity and 98-100%
specificity). Of the mentioned studies, approximately 400 unique patients were
evaluated. Moreover, in these studies, ctDNA has shown significant lead time
over radiographic imaging for the detection of relapse. In TRAcking non-small
cell lung cancer (NSCLC) Evolution through therapy (TRACERx), a prospective
study phylogenetically profiling and monitoring (from diagnosis to death) the
clonal evolution of tumors in 100 NSCLC patients, the median interval between
ctDNA detection and detection of relapse by imaging was 70 days (range 10 to
346 days); in some of these cases, lead times of more than 6 months were
observed.9 In some cases, further subclonal analysis revealed targetable
mutations and amplification events implicated in driving the relapse, thereby
also impacting the therapeutic options available to a given patient.9 Another
longitudinal study in breast cancer patients found that plasma ctDNA was
detected before clinical or radiologic relapse in 16 of 18 relapsed patients;
moreover, ctDNA predicted metastatic relapse with a lead time of up to 2
years.11 A prospective study evaluating ctDNA before and after surgery and
during chemotherapy in patients with locally advanced bladder cancer found
that the dynamics of ctDNA during treatment is a good predictor of outcome and
a better predictor of treatment efficacy than pathologic downstaging.
Moreover, in this study, patients without clearance of ctDNA had a response
rate of 0%.10 ctDNA has also been shown to accurately monitor the activity and
diagnose recurrence of endometrial cancer,13 and multiple studies have found
it to be highly sensitive for monitoring and predicting disease progression
and response to therapy in patients with metastatic melanoma.14,15

_**MRD in monitoring of therapeutic interventions**_

Immune check point inhibitors (ICI) have emerged as an effective therapy and
have been approved for various types of solid tumor malignancies. However, in
most settings only a minority of patients respond to immunotherapy16. FDA
labels for ICI therapies call for treatment until disease progression or
unacceptable toxicity, however there is no definitive guidance on the method
for evaluation of disease progression, which leaves this determination up to
the judgement of clinicians prescribing these drugs17-22.

The determination as to whether a tumor is progressing is currently based
largely on repeated radiographic evaluation of the tumor23. While tumor growth
is often associated with progression, this is complicated by pseudo-
progression, where immune cell infiltration may cause the tumor to initially
appear larger on a scan prior to shrinking, making it difficult to ascertain
in a timely fashion who is responding to treatment and who is not responding
based on radiographic imaging and complicating patient management 24,25.

Numerous peer-reviewed studies have reported that monitoring of ctDNA levels,
in conjunction with radiological assessment, may be a clinically valid method
of assessing the efficacy of ICI, and may help differentiate between
progression and pseudo-progression25-29. These studies have ranged across many
cancer types and multiple different types of immunotherapy, and have shown
that a decreasing level of ctDNA during treatment ("molecular response") is a
potential indicator of treatment response, while an increasing level of ctDNA
during treatment ("molecular progression") is a potential indicator of
treatment non-response. The INSPIRE trial, a Phase II clinical trial using the
Signatera MRD test for monitoring ICI use, identified tumor ctDNA for
monitoring MRD in 98% of patients, wherein the test was able to identify non-
responders with a positive predictive value (PPV) of 98%.30 When evaluated in
conjunction with imaging results, the study reported 100% PPV. In these
patients with molecular progression (30/94), the objective response rate (ORR)
was zero percent (0%) and the 6-month progression free survival (PFS) was
zero.30

_**MRD in hematopoietic malignancies**_

MRD use in certain hematological malignancies has been well established in the
scientific literature and is used as a patient risk stratification tool and to
guide treatment decisions. This is true in both the myeloid and lymphoid
leukemias, and is increasingly apparent in certain lymphomas.31 In chronic
myeloid leukemia (CML), BCR-ABL PCR tests are well-known to reliably detect
the presence of leukemic cells at levels as low as 1 tumor cell per 100,000
normal cells.31 In acute lymphoblastic leukemia (ALL), Multiple Myeloma (MM),
and Chronic Lymphocytic Leukemia (CLL), some MRD tests have demonstrated the
ability to reliably detect and monitor tumor DNA from as little as 200-500ng
DNA .32

The goal of treatment in many hematologic malignancies has been to achieve a
complete response (CR) based on morphologic or surrogate markers, and/or
imaging. However, it is well-established that conventional CR is an
insufficient definition of response, as many patients who achieve CR using
conventional methods still harbor MRD, which can be significantly more
predictive of poor outcomes.33-42

Below is a brief review:

_Acute Myeloid Leukemia (AML) and Myelodysplastic Syndrome (MDS)_

In AML, the goal for patients after chemotherapy is to achieve complete
remission (CR) without evidence of MRD.43,44 However, it is well-known that
conventional morphologic techniques may miss MRD that is below the threshold
of detection, and approximately 50% of patients relapse, despite having
achieved CR by standard morphologic criteria.36,37,45 The presence of MRD in
AML indicates worse prognosis, and lower survival and relapse-free
survival.43,44,46 Further, various therapeutic interventions may be
differentially considered, depending on the molecular MRD risk assessment. For
example, allogeneic hematopoietic stem cell transplant (HSCT) for persistent
MRD in certain types of AML, such as t(8;21), may improve survival compared
with continuation of standard therapy.47 Therefore, MRD testing can be useful
in determining whether a patient should be referred for allogeneic HSCT in
cases of persistent MRD.46-49 Moreover, in acute promyelocytic leukemia (APL),
the detectable presence of the promyelocytic leukemia-retinoic receptor alpha
(PML-RARA) fusion has been shown to predict relapse, and therapy at the time
of molecular relapse has been reported to improve survival compared with
therapy at the time of hematologic relapse.50 Finally, the relapse prevention
with azacitidine (RELAZA2) clinical trial found that pre-emptive therapy was
able to prevent or substantially delay relapse in high-risk MRD-positive
patients with MDS or AML.51

NCCN and the European LeukemiaNet (ELN) MRD Working Party guidelines support
the use of MRD testing in AML.37,43-45 MRD assessment methodologies in AML/APL
include the use flow cytometric methods (FC) as well as cytogenetic and
molecular methods.37,45 Molecular MRD assessment includes single-gene real-
time quantitative PCR (RT-qPCR) for patients that harbor 'suitable' gene
mutations, rearrangements and fusions. These include the nucleophosmin (NPM1)
mutations and PML-RARA fusion in APL, as well as the Runt-related
transcription factor 1 fusion (RUNX1-RUNX1T1), core binding factor-myosin
heavy chain 11 fusion (CBFB-MYH11), and NPM1 mutations in AML; therefore,
molecular MRD is routinely assessed in APL, CBF-AML, and NPM1-mutated
AML.37,45 Many other gene aberrations commonly diagnosed in AML, such as fms-
like tyrosine kinase 3- internal tandem duplication (FLT3-ITD), are not
appropriate for MRD testing, as they may not be stable at relapse due to
frequent gains and losses.37,45 However, MRD monitoring is expanding and is
expected to become routinely used in additional types of AML and for more
suitable gene mutations.37,45 Molecular MRD assessment may also include multi-
gene sequencing (i.e., NGS); however, targeted PCR-based assays for MRD
testing in AML have historically demonstrated superior sensitivity and are not
confounded by clonal hematopoiesis of indeterminate potential (CHIP, discussed
in further detail below) making them less challenging to interpret than
NGS.45,52,53 NGS, however, has recently demonstrated increased sensitivity
such that NGS is expected to become a more commonly used and versatile
approach to MRD testing in AML.53-55

_Chronic Myeloid Leukemia (CML)_

RT-qPCR for the Breakpoint Cluster Region- Tyrosine Kinase ABL1 (BCR-ABL1)
gene fusion, also known as the Philadelphia Chromosome (Ph+), is the current
gold standard for MRD testing in CML. Results of BCR-ABL1 provide information
regarding molecular response (MR) as well as the potential for tyrosine-kinase
(TKI)-resistant disease, allowing for subsequent changes to patient
management.56 In CML, there exist well-established targets and molecular
response milestones over time such that testing can guide therapeutic
decision-making, including the need to switch therapies, refer for allogeneic
HSCT, or discontinue TKI therapy.56 Moreover, discontinuation of TKI therapy
is reliant on a qPCR with a sensitivity of detection of at least BCR-ABL1
international scale (IS) 0.0032% (molecular response (MR)4.5), with a time to
results of less than 2 weeks.56 For patients who do not achieve response
milestones, BRC-ABL1 kinase domain mutational analysis and bone marrow
cytogenetic analysis may be performed.56

Studies have shown that CML patients with certain rare variant transcripts of
BCR-ABL1 have a worse outcome than patients with the most common BCR-ABL1
fusion, and that this may also be relevant for TKI therapy outcomes.57,58
However, most laboratories do not perform testing for atypical transcripts;
moreover, standardization to the IS is not available for these transcripts.59
Though monitoring in such cases may be performed by fluorescence in situ
hybridization (FISH), amplification-based approaches, such as multiplex PCR,
have shown promise for MRD testing in CML patients with atypical BCR-ABL1
transcripts.57-59

Resistance mutations in non-BCR-ABL1 genes have also been associated with poor
outcomes and resistance to TKIs.56,60 The NEXT-in-CML study, a prospective
multicenter study evaluating 236 CML patients with failure or warning response
to TKI therapy, found that NGS detected mutations in 47% of patients, while
sanger sequencing (SS) detected mutations in only 25%; NGS additionally
detected clonally complex mutations (including compound mutants) that were
missed by SS.60 Therefore, for patients who do not achieve response
milestones, as well as for patients with no identifiable BCR-ABL1 mutations,
NGS with a myeloid mutation panel is recommended by the ELN61 and NCCN
guidelines.56

_Acute Lymphocytic Leukemia (ALL)_

MRD is used in ALL patients to monitor complete response (CR) duration and to
make treatment decisions. NCCN guidelines recommend the use of MRD testing in
these patients62. The most common genetic aberration in these patients is the
Philadelphia Chromosome (Ph+) and patients with this alteration are less
likely to respond to chemotherapies and have traditionally had worse
outcomes63. Selective targeted therapies have been created that have resulted
in improved outcomes for these patients, but about one third of these patients
will relapse. A systematic literature review in late 2019 of MRD use in adult
B-cell acute lymphoblastic leukemia (B-ALL), the most common subtype of ALL,
included 23 articles and abstracts and describes the common uses of MRD and
describes the clinical validity and utility of the test across these
studies64. The most frequently employed MRD tests includes flow cytometry, RT-
qPCR for fusion genes (such as BCR-ABL1) and NGS-based assays to detect clonal
rearrangements in immunoglobulin heavy chain (IgH) genes and/or T-cell
receptor (TCR) genes.62,64 The review found that MRD status was consistently
demonstrated to be predictive of overall survival and could be used to assess
patient risk stratification and treatment response. MRD was shown to be useful
after induction chemotherapy to identify the quality of response when
morphological remission is obtained, as well as a predictor for pending
relapse in these patients. The predictive ability of MRD is present regardless
of Ph status.

__

_Multiple Myeloma (MM)_

Immunomodulatory drugs, such as lenalidomide, and proteasome inhibitors have
become available to MM patients and allow for a large percentage to achieve
CR. However, many patients will relapse.33 A large-cohort (14 studies) meta-
analysis in 2017 demonstrated the clinical validity of MRD testing to predict
survival outcomes, including in patients that demonstrated CR, and utility in
treatment selection.38 It was also demonstrated to be useful in monitoring
maintenance therapy.39,65-67 As in ALL, CLL, and lymphoma, a primary molecular
target for MRD assessment in MM is IgH.68,69 Use of MRD testing is required
for the assessment of relapse in the 2021 NCCN Guidelines for MM.69

__

_Chronic Lymphocytic Leukemia (CLL)_

Although many CLL patients have prolonged survival or cure after treatment
with fludarabine, cyclophosphamide, and rituximab, the risk of relapse
remains.70 Flow cytometry is an accepted method for risk stratification of
patients and assessment for CR after treatment to assess residual disease,
however NGS-based MRD was demonstrated to be more sensitive and a better
predictor of patient outcomes, possibly because other methods are not
sensitive enough to accurately predict CR.39,40 As in ALL, MM and lymphoma, a
primary molecular target for MRD assessment in CLL is IgH.71,72 2021 NCCN
Guidelines describes MRD testing as an important predictor of treatment
efficacy and describes NGS-based methods as more sensitive than PCR or flow
cytometry based testing.72

_Lymphoma_

Although many patients with a B-cell lymphoma (BCL) experience prolonged
remission or achieve cure after systemic therapy, many will relapse and suffer
adverse outcomes.73 There is substantial evidence that measurement of MRD in
different types of BCL using various cell free DNA (cfDNA) profiling assays
can characterize risk and detect residual disease earlier than clinical
relapse.34,35,74-78 MRD testing with cfDNA has shown improved sensitivity and
specificity compared with computerized tomography (CT) and positron
emission/CT (PET/CT) traditionally used in disease surveillance, with lead
times of 3-6 months for the detection of relapse.34,35,74,75,77-79 The use of
ctDNA MRD tests in lymphoma may therefore allow for a reduction in the
frequency of surveillance imaging, with a consequent reduction in radiation
exposure, a potential health risk emphasized by lymphoma
investigators.34,35,77,80

In addition to assessment of disease burden, prognostication, and monitoring
for relapse, ctDNA tests for MRD in lymphoma may allow for the customization
of therapy ("risk-adapted" strategies) and initiation of pre-emptive therapy
designed to prevent overt clinical relapse.80,81 In 1 study monitoring 183
mantle cell lymphoma patients after autologous stem cell transplantation, pre-
emptive rituximab was administered to patients with evidence of molecular
relapse; the patients treated pre-emptively converted to MRD negativity.81
Though the results were uncontrolled, the authors acknowledge that this likely
resulted in a delay in overt clinical relapse.81 Another study in Hodgkin
lymphoma patients found that MRD testing using ctDNA can track clonal gene
evolution and monitor residual disease during multiagent chemotherapy.42 The
authors highlight that this approach to MRD testing can complement PET/CT and
identify patients likely to be chemorefractory, with the goal of informing
early treatment intensification (or de-escalation, in the case of unlikely
chemoresistance).42

Importantly, it is not uncommon for lymphoma patients who ultimately become
ctDNA-positive to have had 1 prior ctDNA-negative results, highlighting the
utility of serial disease monitoring over time.34,35 NCCN guidelines support
the use of molecular analysis in the differential diagnosis of BCL, to detect
IgH and TCR gene rearrangements.73 Various highly-sensitive NGS-based
techniques are available for detecting MRD in lymphoma.75,78 However, despite
their high sensitivity for detecting MRD, the implementation of MRD testing
into routine MRD protocols has not been optimized in B or T-cell
lymphomas.76,82

**_Limitations of ctDNA for MRD assessment_**

MRD testing using ctDNA is not without limitations and challenges in
interpretation. Discordance of mutations found between ctDNA and tissue is
well-described and can occur in a significant proportion of cases.83-86
Reasons for this are varied and include tumor heterogeneity, clonal evolution,
and time of sampling (i.e., contemporaneous vs remote sampling between ctDNA
and tissue). Studies have also reported that ctDNA may be enriched for therapy
resistance alterations as well as for variants associated with CHIP (sometimes
referred to as age-related clonal hematopoiesis, or 'ARCH').83,85-87 **** CHIP
is known to increase with age and occurs in 10->30% of adults over 70 years of
age.86-89 In 1 study of CRC patients, 17% of the pre-operative cell-free DNA
mutations were determined to be CHIP and persisted post-operatively as well as
after chemotherapy.86 In another study in advanced prostate cancer patients,
CHIP variants accounted for nearly half of the cell-free somatic DNA repair
gene variants detected.87 Importantly, many of these DNA repair genes are used
for determination of eligibility for poly(ADP) ribose polymerase inhibitors
(PARPi) therapy. In the study by Jensen et al., if a whole blood control had
not been performed, 10% of patients would have been incorrectly considered
eligible for PARPi therapy as a result of CHIP interference.87
Misclassification of CHIP as tumor-derived mutations can therefore lead to
incorrect evaluation of residual disease as well as subsequent inappropriate
treatment. For these reasons, some researchers have advocated for the use of
paired ctDNA testing, using paired peripheral blood cell or tumor tissue as
one potential approach to testing.85-87 There may be other approaches (i.e.,
algorithms and filters based on known population frequencies of genetic
variants) to mitigate confounding by CHIP. This is an ongoing area of
investigation.

Further, as ctDNA for MRD testing is specific to a given tumor, testing cannot
be used to detect a second primary tumor, including 1 located within the same
organ (i.e., 2 separate primary lung tumors). Testing by this methodology also
requires the presence of sufficient ctDNA molecules in the plasma (or other
tested compartment), a special consideration particularly in patients with
smaller or less aggressive cancers. Finally, it is critical that MRD tests
achieve high sensitivities at limits of detection significantly lower than
those typically attained by NGS tests used for diagnosis.

The reviewed evidence supports that MRD testing can be used to accurately
predict disease recurrence or progression before clinical or radiographical
evidence is evident (establishing molecular recurrence) and performs better
than other established methods for disease surveillance such as serial CEA
monitoring, physical exams, imaging or flow cytometry. Although this is a
logical progression of our understanding of the development and evolution of
cancer (that tumor cells grow and shed DNA at proportional levels until such a
time there is macroscopic disease in organs or bone marrow), the evidence
presented above clearly establishes that MRD testing can demonstrate
acceptable clinical validity in the determination of disease recurrence; a
condition whose identification has pre-established utility as it is an event
that in the proper clinical context requires altering or modifying patient
management. Current medical practice, including as defined in the NCCN
guidelines, clearly advocate for changing or re-establishing treatment when
such a diagnosis is rendered. As such, determining molecular recurrence before
there is clinical or radiographical evidence of it is likely to further
improve patient outcomes and is consistent with current guidelines that
advocate for early detection of and treatment for recurrence. Furthermore,
additional uses of MRD have been established, such as for monitoring treatment
response, although it is based on the same principle. The studies described
above again demonstrate the clinical validity of molecular progression as
predictive of failure to respond to treatment and demonstrate futility in
continued therapy. The utility of such testing in maintenance therapy
monitoring to improve patient outcomes is therefore similarly inherent;
preclusion of potentially hazardous compounds that are not likely to have
clinical benefit and prevention of adverse events have demonstrated improved
patient outcomes.

This remains a rapidly evolving field, and we anticipate that new evidence may
emerge either showing limitations of the clinical utility underlying MRD
testing or additional strengths and new applications. Additionally, this
coverage decision is based heavily on paradigm for care which was not
developed for MRD testing. In summary, we anticipate future revisions to this
coverage decision as the science and standard of care evolves, which may
further limit or expand coverage for MRD testing.