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\begin{document}

\title{Role of Bone Marrow Biopsy for Staging New Patients with Ewing Sarcoma:
A Systematic Review}



\author[1]{Kevin Campbell}%
\author[2]{David Shulman}%
\author[3]{Holcombe Grier}%
\author[4]{Steven DuBois}%
\affil[1]{Children's Hospital Boston}%
\affil[2]{Boston Children's Hospital}%
\affil[3]{Dana Farber Cancer Institute}%
\affil[4]{Dana-Farber Cancer Institute}%


\vspace{-1em}



  
  \date{May 04, 2024}


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\selectlanguage{english}
\begin{abstract}
The incidence of bone marrow metastasis (BMM) in newly diagnosed Ewing
sarcoma (ES) is variable across studies. An optimal staging strategy for
detecting BMM is not defined. While BM biopsy and/or aspirate (BMBA)
have been the gold standard, {[}F-18{]}fluorodeoxyglucose positron
emission tomography (FDG-PET) to detect BM metastasis may decrease
reliance on BMBA. We conducted a systematic review to assess incidence
of BMM and the role of FDG-PET. We observed a pooled incidence by BMBA
of BMM of 4.8\% in all newly diagnosed ES patients and 17.5\% among
patients with metastatic disease. Only 1.2\% of patients had BMM as
their sole metastatic site. FDG-PET detection of BMM compared to BMBA
demonstrated pooled 100\% sensitivity and 96\% specificity, positive
predictive value of 75\% and negative predictive value of 100\%. In the
era of FDG-PET imaging, omission of BMBA may be considered in patients
with otherwise localized disease after initial staging studies.%
\end{abstract}%



\sloppy


\textbf{1.~~~} \textbf{Introduction}

Ewing sarcoma (ES) is an aggressive cancer of the bone and/or soft
tissue and has peak incidence in the adolescent and young adult
population. Behind osteosarcoma, it is the second most common bone
cancer found in children, comprising 10-15\% of all primary malignancies
of the bone.{[}1{]} At initial diagnosis, metastatic status is the most
important prognostic factor, with survival rates diverging for patients
with localized disease compared to those presenting with metastatic
disease.{[}2{]} Common sites of metastasis include the lungs and bone,
with bone marrow (BM) metastasis less commonly reported. Among patients
with metastatic disease, those with lung metastases alone have a better
prognosis, with event-free survival (EFS) ranging from 29-52\% while
patients with bone/BM metastases have an EFS of 20\% or lower.{[}2,3{]}
Metastatic BM involvement has further been reported as an independent
risk factor distinct from multiple bone metastasis.{[}2,4,5{]} In one
large analysis, patients with both BM and bone metastasis had inferior
3-year OS and EFS (21\% and 14\%) compared to patients with bone
metastasis but no BM metastasis (37\% and 31\%).{[}2{]} Accurate
identification of metastatic pattern is important in determining
treatment, monitoring response, and determining prognosis.

Staging usually includes imaging of the primary site plus evaluation of
metastatic disease with a chest CT (computed tomography),
{[}F-18{]}fluorodeoxyglucose positron emission tomography (FDG-PET)
scan, and bone marrow biopsy and aspirate (BMBA). The current gold
standard evaluation for detection of metastatic BM disease has been
BMBA. For example, the Children's Oncology Group required this procedure
for enrollment on the last two protocols for patients with newly
diagnosed disease. In adult patients with primary bone cancer, a BMBA is
not routinely performed, and the current National Comprehensive Cancer
Networks (NCCN) guidelines recommend an MRI of the spine and pelvis as
an alternative to BMBA. {[}6{]} ~A BMBA procedure is invasive and
carries a small risk of complications,{[}7{]} including risks of general
anesthesia administration in young patients. The increased use of
FDG-PET scan, a non-invasive technique allowing for whole-body staging,
has prompted investigators to ask if this modality may replace BMBA for
detection of BM metastasis,{[}8-12{]} with several cohort studies
directly comparing FDG-PET to BMBA in detection of BM metastasis.
{[}13-18{]} Other studies have evaluated the use of FDG-PET/CT scan in
ES and rhabdomyosarcoma and demonstrated FDG-PET scan to have a high
sensitivity and specificity for detection of bone metastases when
compared to bone scan and MRI.{[}17,19-22{]} FDG-PET scans have been
shown to be superior to bone scans to detect asymptomatic metastasis in
ES patients.{[}15{]}

To provide clarity on the incidence of metastatic BM disease in ES and
the best strategy to diagnose BM disease at presentation in these
patients, we pooled available evidence in this systematic review. First,
we describe the incidence of metastatic BM disease with and without the
presence of additional metastatic disease in the presentation of newly
diagnosed ES as well as clinical associations with BM metastatic
disease. Second, we report the available sensitivity, specificity,
positive predictive value (PPV) and negative predictive value (NPV) of
FDG-PET scans for diagnosis of metastatic BM disease in newly diagnosed
ES patients.

\par\null

\textbf{2. Methods}

This review was conducted according to the Preferred Reporting Items for
Systematic Reviews and Meta-analyses (PRISMA) guidelines {[}16{]}. The
review protocol for this study was prospectively registered at PROSPERO
(registration number 179382).

\emph{2.1 Search strategy}

Searches were conducted in April 2020 in three publicly available
databases: PubMed; Google Scholar; and Cochrane Library. Search strategy
involved an iterative process in which keywords for searches were a
combination of one diagnosis name and one topic name. The Ewing sarcoma
family tumors (ESFT) historically included a family of morphologically
similar malignancies but with diverging names. Thus, five diagnosis
search terms were utilized: Ewing sarcoma; Ewing's sarcoma; Peripheral
Neuroectodermal Tumor; PNET; and Askin Tumor. Alongside a diagnosis
term, 13 topic search terms were utilized: bone marrow; bone marrow
biopsy; bone marrow aspirate; Positron Emission Tomography; PET;
metastatic; metastatic pattern; metastasis; randomized; phase III;
clinical trial; staging; and diagnosis. This process resulted in 65
individual searches (5 diagnosis terms x 13 topic terms) for each of the
3 databases utilized (195 total searches across all databases). For each
search, a single reviewer documented the number of results, the number
of abstracts read and the number of articles meeting criteria to be
shared with a second reviewer for final approval. A third reviewer was
available to resolve any discrepancies. Searches resulting in
\textgreater{}500 results were edited to restrict specific keywords
deemed irrelevant to this study. For example, the PubMed search of
`Primitive Neuroectodermal Tumor' + `metastatic' yielded 4,129 results.
After designating the search not return articles with keywords `case
report,' `neuroblastoma,' `medulloblastoma,' and `pancreatic,' results
decreased to 284 articles. To expand our search, references of the
retrieved articles were also screened for additional studies.

\emph{2.2. Eligibility criteria}

Clinical trials (phase I, II and III), prospective and retrospective
cohort studies, cross-sectional studies, and case series of patients
with ES were all considered for inclusion in this review. Case reports,
reviews, viewpoints or conference reports were excluded. Studies in
non-English language were excluded. Results from 1970-2020 were
included, though studies incorporating data both after and before 1970
were excluded if it was unclear which data/patients met inclusion
criteria for dates. If data were identified to be reported in
\textgreater{}1 study, the study with the higher `n' was selected.

\emph{Data extraction}

The data collected for each study in the systematic review included:
authors; journal; year of publication; country of origin; study design;
study population; and study sample size. For references providing only
aggregate data, the following were collected: percentage of patients
with BM metastasis; percentage of patients with isolated BM metastasis;
clinical predictors of BM metastasis; sensitivity of FDG-PET scans to
detect BM metastasis; specificity of FDG-PET scans to exclude BM
metastasis; PPV of positive FDG-PET scans for ``true'' BM metastasis by
biopsy; NPV of negative FDG-PET scans for no BM metastasis by biopsy;
and any other imaging features associated with BM metastasis. For
references providing patient level data, the following was also
collected when available: age of each ES patient; primary tumor site of
each ES patient; BM metastasis status (if present, subcategorized as
either isolated BM metastasis vs BM + additional areas of metastasis);
results of FDG-PET scan if completed at diagnosis; and results of
unilateral or bilateral BMBA at diagnosis (if yes, was BM disease
identified).

2.4. \emph{Data synthesis}

To determine the incidence of BM metastasis in newly diagnosed ES
patients, studies reporting newly diagnosed BM metastatic disease in a
homogenous background population of all newly diagnosed ES patients were
included. Studies reporting the incidence of BM metastatic disease in
patients with metastatic disease were used for a separate calculation.
The number of patients from each study was totaled to provide each
patient with uniform weight in calculations of descriptive statistics.

To determine the sensitivity, specificity, PPV and NPV of FDG-PET scans
in comparison to BMBA for the presence of BM metastasis in newly
diagnosed ES patients, studies were included if results of FDG-PET scans
and BMBA for diagnosis of BM metastasis were provided. A study was
considered to sufficiently report on the status of BM metastasis via
FDG-PET scan if it reported FDG-PET BM results separately from primary
tumor or metastatic bone lesions. Studies were excluded if they reported
the incidence of bone metastasis but not BM metastasis by FDG-PET scans.

\textbf{3. Results}

3.1. \emph{Study selection}

The initial search identified 11,110 titles reviewed (PubMed: 8,324;
Google Scholar: 1,208; Cochrane library: 1,578). Reviewer 1 read 330
abstracts, from which 97 articles (including 17 articles screened from
references) were flagged for Reviewer 2 (Fig. 1). Seventy-five articles
were identified for full-text review. Of these, 37 were deemed
ineligible for inclusion due to the following reasons: 18 did not report
incidence of BM metastasis; 7 did not utilize FDG-PET scans to assess
for BM metastasis; 6 had missing data on diagnostic testing used for
metastatic disease; 4 were not in English; 2 involved patients with
diseases other than ES.

3.2 \emph{Quantitative analysis: Incidence of BM metastasis}

We identified 10 studies providing quantitative data describing the
incidence of BM metastasis in all unselected patients with newly
diagnosed ES (Table 1).{[}21,23-31{]} These studies ranged in year of
publication from 1995 -- 2020. Eight studies were completed in a
retrospective manner, one was a phase 3 clinical trial and one was a
pilot trial. Combined, they comprise 1,663 patients (median 75
patients/study; range 17 -- 647 patients).

Of the total of 1,663 patients, 79 had BM metastasis, for an incidence
of 4.8\% in this unselected group of patients. Among the 450 patients
with any metastatic disease, the incidence of BM disease was 17.5\%
(79/450). Three studies reported the presence or absence of isolated BM
metastases, with 1.2\% (8/692) of patients with isolated BM
metastasis.{[}24,25,27{]} Ten additional patients with isolated BM
metastatic disease were identified in the literature for a total of 18.
Eight of these 18 cases reported the location of the primary tumor:
three pelvic primary tumors and five located in the appendicular
skeleton.

We identified an additional 8 studies for which inclusion was restricted
to newly diagnosed ES patients with metastatic disease only or a
specific subset of metastatic ES. Five of these studies reported the
incidence of BM metastasis in a selected population of ES patients
(Table 2).{[}2,32-35{]} Of these, three excluded patients with newly
diagnosed localized ES and reported on 934 total patients with newly
diagnosed metastatic ES. Of these, 19.0\% were reported to have BM
metastasis. Two other studies describe further subsets of metastatic ES
patients. One excluded patients with lung only metastatic disease and
reported an incidence of BM metastasis of 43.8\% (123/281).{[}2{]} A
second study limited its inclusion to patients with metastatic bone ES
and reported an incidence of BM metastasis of 23.7\% (23/97).{[}35{]}

Two additional studies in patients with metastatic disease reported
patients with isolated BM metastatic disease without providing an
incidence of any BM metastasis. One study reported 7\% (8/110) of
patients with newly diagnosed metastatic ES to present with isolated BM
metastasis,{[}36{]} another reported 3.3\% (2/60) incidence of isolated
BM metastatic disease.{[}37{]}

Patients with isolated lung metastasis have superior outcomes compared
to patients with other metastasis.{[}3{]} Since detecting BM metastasis
in patients who might otherwise have a more favorable outcome may
provide important prognostic information, we also assessed the frequency
of BM metastases in patients with lung metastasis but lacking bone
metastases. We evaluated all studies included in Tables 1 2. Six of the
15 studies analyzed reported relevant data, with 8.8\% (20/225) of
patients with reported lung metastatic disease also having BM metastasis
but not bone metastasis.

3.3 \emph{Quantitative analysis: FDG-PET scan vs. BMBA}

Four studies (Table 3) were identified which utilized FDG-PET scans for
staging of BM metastasis in newly diagnosed ES
patients.{[}21,29,38,39{]} Data from these studies were aggregated for
quantitative analysis to define testing characteristics of FDG-PET scans
compared to BMBA. The studies ranged in publication year from 2013 -
2019 and all were completed in a retrospective manner. Combined, these
studies comprised 142 patients (median 23 patients/study; range 16-80
patients).

Pooled patient level data were used to construct a contingency table to
determine sensitivity, specificity, PPV and NPV. Results revealed
FDG-PET scans to have a sensitivity of 100\% (3/3) and specificity of
96\% (96/100) to detect BM metastasis. Compared to BM biopsy, the PPV of
a positive FDG-PET scan was found to be 75\% (3/4) and the NPV of a
negative FDG-PET scan was 100\% (106/106). The patient with a negative
BMBA but positive FDG-PET scan was identified by Kasalek et al on
FDG-PET scan to have BM metastatic lesions involving bilateral posterior
iliac crest and extensive BM involvement elsewhere in the axial and
appendicular skeleton. {[}38{]}

3.4 \emph{Qualitative analysis}

Several studies were selected for inclusion in our review based upon
qualitative analysis or descriptive findings contributing to the
understanding of the incidence of BM disease at presentation in ES as
well as the advantages and disadvantages to BMBA and FDG-PET scan in
assessment of BM metastatic disease.

The most common reported association for patients with BM metastasis was
the presence of other metastatic lesions, and specifically bone
metastasis. Kopp et al found BMBA to be positive in 41.9\% (13/31) of
patients with the presence of other metastatic but 0\% (0/85) in ES
patients with non-metastatic disease.{[}26{]} A positive association of
the number of bone metastatic lesions and presence of BM metastasis was
reported by Inagaki et al. Of 26 patients with newly diagnosed ES, 100\%
(3/3) of patients with BM metastasis had bone metastases and 4.3\%
(1/23) patients without BM metastases had bone metastases.{[}29{]}
Newman et al reported 0 of 91 ES patients with BM metastases in cases
without osseous metastatic disease.{[}21{]} Khan et al reported that
45.5\% (5/11) of patients with BM mets had concurrent bone metastatic
disease.{[}25{]}

Additionally, BM metastasis was reported to be associated with primary
tumors of the pelvis, large tumor size, and presentation with fever
and/or elevated lactate dehydrogenase (LDH) level. Two studies reported
that pelvic primary site was significantly associated with BM metastatic
disease at diagnosis. One reported a risk of BM involvement three times
higher in patients with pelvic lesions compared with other primary
sites; the second reported BM involvement in 22\% (13/59) of patients
with pelvic primary disease.{[}24,27{]} Tumor diameter ([?]80mm) and LDH
level at diagnosis (\textgreater{} x ULN) were reported to be factors
significantly related to BM involvement by Inagaki et al.{[}29{]}
Oberlin et al reported fever at diagnosis was significantly associated
with the presence of BM metastasis.{[}27{]}

One study analyzed the concordance between BM aspirate (BMA) and BM
biopsy (BMB). Among 59 patients with bilateral BMA and 62 patients with
bilateral BMB, concordance rates between sides were 97\% and 98\%,
respectively. BMB was concluded to be more sensitive to detect
metastatic disease than BMA as 100\% (4/4) cases of positive BMA were
also found to have positive BMB, three positive BMB procedures had
negative ipsilateral BMA.{[}21{]} In a study including adult patients
with various types of sarcoma, discrepancies in findings of metastatic
disease between bilateral samples by morphologic evaluation were found
in 29\% of (27/94) of cases.{[}40{]}

\textbf{4. Discussion}

To our knowledge, this systematic review is the first to describe the
incidence of metastatic BM disease with and without the presence of
additional metastatic disease in newly diagnosed ES patients, as well as
report the testing characteristics of FDG-PET scans in the diagnosis of
metastatic BM disease in this population.

Our results indicate a pooled incidence of BM metastasis of 4.8\% in all
patients with newly diagnosed ES and 17.5\% in patients with other
clinically or radiographically apparent metastatic disease. Further,
8.8\% of patients with known lung metastasis were reported to have BM
but not bone metastasis. FDG-PET scan demonstrates a sensitivity and
specificity of 100\% and 96\%, and a PPV and NPV of 75\% and 100\% to
detect BM metastatic disease compared to BMBA. Given these findings, we
have modified our local practice as follows. During initial workup in
patients with newly diagnosed ES presenting with clinical or
radiographic (including FDG-PET scan) evidence of metastatic disease, we
obtain BMBA as this information may provide information relevant to
prognosis, response assessment, and understanding potential delays due
to slow blood count recovery. In the specific setting of isolated
pulmonary metastasis on staging studies obtained prior to BMBA, the
incidence of detecting BM metastatic disease appears high enough and the
prognostic impact of a positive finding great enough to make this a
particularly important population to evaluate by BMBA. On the converse,
one may reasonably conclude that detecting BM metastasis in patients
with known bone metastasis provides only modest additional prognostic
information. Our local practice nevertheless still includes BMBA for
such patients to obtain full extent of disease at baseline, which may
inform response, toxicity assessment, and prognosis. In patients with no
evidence of metastases including no BM uptake on FDG-PET scan, we now
omit BMBA as part of routine staging, unless there are clinical concerns
(e.g., findings on peripheral complete blood count) or clinical trial
requirements. This latter approach is consistent with conclusions drawn
by several studies included in this review.{[}21,24,26,29{]} While some
studies reported an association of BM metastasis disease with primary
tumors of the pelvis, {[}24,27{]} it is not clear if this finding
represents sampling of primary tumor tissue during BMBA procedure. Based
upon the available evidence, we do not recommend bone marrow sampling in
the setting of a primary pelvic tumor if diagnostic workup reveals no
concern for metastatic lesions.

Though rare, we identified 18 reported cases of newly diagnosed ES
patients with isolated BM metastasis.{[}24,25,27,36,37{]} In eight
cases, location of the primary tumor was provided, with 63\% (5/8)
reporting location in the appendicular skeleton.{[}24,25,27{]} On review
of these individual cases, no significant associations to aid in their
identification was observed. In 16 of 18 cases, staging workup was
reported. All 16 cases included MRI of the primary site, CT scan of the
chest as well as bone scan to evaluate the presence/absence of
metastatic disease. FDG-PET scans, a relatively newer technology, were
not reported during initial workup.

We acknowledge that our approach to omit BMBA at initial staging in
patients without other metastasis may miss this very rare subgroup of
patients with isolated BM metastasis. However, the available data
support a role for using FDG-PET scan as a screening tool for assessment
for BM disease. We found no reported cases of false negative findings of
BM metastatic disease by use of FDG-PET scan (sensitivity and NPV of
100\%). Thus, when FDG-PET scan is negative for BM metastasis or other
metastasis, omission of BMBA seems reasonable. When FDG-PET scan
demonstrates BM metastasis by imaging, the decision to perform a
confirmatory BMBA may be based upon the overall clinical context. For
example, an FDG-PET scan demonstrating a positive BM signal in the
context of widespread bone metastasis would likely be viewed differently
from an FDG-PET scan demonstrating only a positive BM signal in a
patient with otherwise localized disease. Given the major prognostic
implications in the latter case, a confirmatory BMBA may be particularly
important clinically. Of note, our review found one reported false
positive case by FDG-PET scan with negative BMBA. However, this assumes
BMBA as the gold standard for diagnosing BM metastasis, but given the
possibility of BM involvement being patchy, this finding may represent a
false negative BMBA.

The role of BM investigation by either a BMB or BMA or by a unilateral
vs bilateral procedure were discussed in several reports. One study
concluded that completing only a BMB or a BMA was inadequate as they
noted BM involvement to be focal in several patients resulting in
frequent discrepancies between aspirates and biopsies at the various
sites explored.{[}27{]} A second study analyzing the ability of BMB vs
BMA and unilateral vs bilateral approach in detection of BM metastatic
disease found BMB and bilateral approach, respectively, were superior in
detecting BM metastases.{[}21{]} Based upon these findings, when
indicated, we obtain bilateral evaluation with bone aspirate and biopsy.

From this systematic review of the literature, the incidence of BM
metastasis is 4.8\% in all patients with newly diagnosed ES and 17.5\%
in patients with clinically apparent metastatic ES. Based upon the
testing characteristics of FDG-PET scans in the diagnosis of metastatic
BM disease in newly diagnosed ES, we now obtain BMBA at initial staging
according to the algorithm in Figure 2. In the absence of specific
extenuating circumstances, we omit staging BMBA in newly diagnosed
patients with no evidence of metastases on other staging studies. In
patients with newly diagnosed ES who have metastatic disease detected by
other staging studies that include an FDG-PET scan, we obtain baseline
BMBA.

\textbf{Conflict of Interest Statement:} SGD reports travel expenses
from Loxo Oncology, Roche, and Salarius and consulting fee from Bayer
and Loxo Oncology.

\textbf{Grant Support:} NIH T32 CA136432-08 (KC) and Alex's Lemonade
Stand Foundation (KC \& DS).

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\textbf{Figure Legends:}

\textbf{Figure 1.} Selection flow chart for studies included in the
systematic review.

\textbf{Figure 2.} Algorithm for bone marrow staging for patients with
newly diagnosed Ewing sarcoma based upon data pooled from systematic
review.

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