A report from the Korean Multiple Myeloma Working Party demonstrated that achieving a CR/near CR nCR be-fore autologous peripheral blood stem cell transplan-tation auto-PBSCT significant
Trang 1Minimal Residual Disease in Myeloma:
Are We There Yet?
Andrew J Hart,1Madan H Jagasia,1Annette S Kim,2Claudio A Mosse,2
Bipin N Savani,1Adetola Kassim1
Measurement of minimal residual disease is routine in diseases such as chronic myelogenous leukemia,
pre-cursor B cell acute lymphoblastic leukemia, and acute promyelocytic leukemia because it provides important
prognostic information However, the role of minimal residual disease testing has not been widely adopted in
multiple myeloma (MM), with other parameters such as the International Staging System (ISS) and
cytoge-netic analysis primarily guiding therapy and determination of prognosis Until recently, achieving a complete
response (CR), as defined by the International Myeloma Working Group (IMWG) criteria, was rare in
pa-tients with MM The use of novel agents with or without autologous peripheral blood stem cell
transplanta-tion (auto-PBSCT) has significantly increased CR rates, thus increasing overall survival (OS) rates The
majority of patients with MM have persistent levels of residual disease that are below the sensitivity of
bone marrow (BM) morphology, protein electrophoresis with immunofixation, and light chain quantitation
even after attaining CR and will eventually relapse Measurement of minimal residual disease by more
sensi-tive methods, and the use of these methods as a tool for predicting patient outcomes and guiding therapeutic
decisions, has thus become more relevant Methods available for monitoring minimal residual disease in MM
include PCR and multiparameter flow cytometry (MFC), both of which have been shown to be valuable in
other hematologic malignancies; however, neither has become a standard of care in MM Here, we review
current evidence for using minimal residual disease measurement for risk assessment in MM as well as
incor-porating pretreatment factors and posttreatment minimal residual disease monitoring as a prognostic tool
for therapeutic decisions, and we outline challenges to developing uniform criteria for minimal residual
dis-ease monitoring
Biol Blood Marrow Transplant 18: 1790-1799 (2012) Ó 2012 American Society for Blood and Marrow Transplantation.
Published by Elsevier Inc All rights reserved.
KEY WORDS: Minimal residual disease, Multiple myeloma, Flow cytometry, PCR
INTRODUCTION
Multiple myeloma (MM) is a very heterogeneous
disease with protean manifestations, as well as an
as-sortment of genetic and molecular alterations, making
prognostic determination at diagnosis quite
challeng-ing In 1975, Durie and Salmon[1]described an MM staging system using features such as tumor cell mass, the presence of end-organ damage, osteolytic bone le-sions, and elevated serum Ig levels More recently, the International Staging System (ISS) was developed that describes disease burden based on b2-microglobulin and serum albumin levels, with both having prognostic significance at diagnosis [2] Cytogenetic abnormali-ties including 13q deletion and detection of t(4;14), t(14;16), and del17p by fluorescence in situ hybridiza-tion (FISH) have been shown to predict a less favorable survival, and the International Myeloma Working Group (IMWG) has proposed a new classification sys-tem based on molecular and cytogenetic criteria [3] Gene expression profiling has also recently been used
to determine high-risk populations but is not available for widespread use[4,5] The use of these molecular and cytogenetic signatures to direct treatment, in the context of other staging parameters, variable disease manifestations, and expanding therapeutic options, is still being validated
From the 1 Department of Medicine, Division of Hematology/
Oncology, Section of Hematology and Stem Cell Transplant;
and 2 Department of Pathology, Microbiology, and
Immunol-ogy, Vanderbilt University Medical Center, Nashville,
Tennessee.
Financial disclosure: See Acknowledgment on page 1797.
Correspondence and reprint requests: Adetola Kassim, MD,
Van-derbilt University Division of Hematology/Oncology, 1301
Medical Center Drive, Suite 3927, Nashville, TN 37232
(e-mail: adetola.kassim@vanderbilt.edu ).
Received March 20, 2012; accepted May 3, 2012
Ó 2012 American Society for Blood and Marrow Transplantation.
Published by Elsevier Inc All rights reserved.
1083-8791/$36.00
doi: 10.1016/j.bbmt.2012.05.009
1790
Trang 2The IMWG response criteria are based on (1)
serum and urine M-protein by electrophoresis and
immunofixation (IFX), (2) percentage of plasma cells
on bone marrow (BM) biopsy, and (3) serum free light
chains (sFLCs) [6] The importance of achieving
a complete response (CR), with an associated benefit
in overall survival (OS), has been well-documented,
although data also show that development of CR has
the most significant benefit in only a small, high-risk
group of patients as defined by gene expression
profiling [7,8] As CR rates have improved, more
rigorous definitions of response have been developed,
including stringent CR (sCR) by the IMWG
that incorporates sFLCs along with
immuno-histochemistry and immunofluorescent techniques to
establish plasma cell (PC) clonality[6] It has been
pro-posed that the sFLC ratio, which has been shown at
di-agnosis to be an independent prognostic factor and
predict more aggressive disease, be incorporated into
the ISS to help improve risk stratification as well
[9-11] The role of sFLC measurement as a minimal
residual disease marker will be further discussed below
Improving CR rates, with associated increases in
OS and event-free survival (EFS), have made the
mea-surement and monitoring of minimal residual disease
in MM with more sensitive techniques a relevant
pur-suit Microscopic BM examination, radiographic
im-aging, molecular, and flow cytometric techniques
have all been used for this purpose Two very sensitive
techniques that have been studied with increasing
fre-quency during the past few years are PCR and
multipa-rameter flow cytometry (MFC) However, for a variety
of reasons including the heterogeneity of the disease
and the technical complexity of some of the
tech-niques, minimal residual disease monitoring with
highly sensitive techniques has not become routine
clinical practice Here, we review the use of these
ap-proaches and outline the challenges to developing
uni-form and available methods for minimal residual
disease measurement in MM
Techniques for Assessing Minimal Residual
Disease in MM
Protein and imaging studies
Measurement of serum and urine paraprotein
levels with IFX, sFLC and urine free light chains,
and morphologic examination of the BM are all widely
available methods used to measure disease burden in
MM One definition of CR is defined by the IMWG
as\5% PCs in the BM with negative serum and urine
IFX, and the clinical significance of achieving CR has
been well-described [6,7] Data from the Total
Therapy trials have demonstrated the importance of
CR on long-term outcomes [12] These treatment
regimens, though, are rigorous and may not be
amena-ble for use outside of large referral centers A report
from the Korean Multiple Myeloma Working Party demonstrated that achieving a CR/near CR (nCR) be-fore autologous peripheral blood stem cell transplan-tation (auto-PBSCT) significantly increased 2-year
OS from 70.9% to 86.6% compared with patients achieving a partial response, providing data that achieving CR has prognostic significance even before high-dose therapy (HDT) and auto-PBSCT[13]
As BM biopsies are expensive, time-consuming, and pose some risk to patients, it has been argued that BM examination is not necessary in patients with negative serum and urine electrophoresis and IFX due to the low likelihood of increased PCs under these circumstances[14] However, the independent value of
BM examination has been examined in 2 studies Data from Chee et al.[15]showed in 92 patients that 14% with negative IFX and 10% of patients with a normal sFLC ratio had $5% BM PCs in the marrow, with clonality demonstrated in 85% of patients with resid-ual PCs[15] In patients who are IFX-negative, they found significantly improved OS from time of IFX-negativity in patients with\5% total PCs compared with those with$5% (6.2 versus 2.3 years; P 5 01) More recently, Fernandez de Larrea et al.[16]showed
in 35 patients after auto-PBSCT that the total number
of PCs present in patients in CR after auto-PBSCT correlates with progression-free survival (PFS) but not OS[16] There was a nonsignificant difference in median OS in patients with#1.5% PCs versus 5% PCs (median OS not reached versus 9.7 years;
P5 195) These results demonstrate that microscopic assessment of the BM can have prognostic significance regardless of the status of protein studies, although the sensitivity of morphology alone is crude and limited by the number of cells evaluated as well as sampling vari-ability
Imaging by fluorodeoxyglucose-positron emission tomography (PET) has also been shown to have prog-nostic significance, with a significant improvement in PFS and OS in patients with 100% standardized up-take value reduction compared with\100% standard-ized uptake value reduction after treatment with thalidomide-dexamethasone and auto-PBSCT in 1 study[17] This held true even among patients other-wise achieving a CR Moreover, they demonstrated
a significant improvement in post-relapse OS if the fluorodeoxyglucose-PET was negative versus positive
at 36 months Although PET imaging is widely avail-able, not all patients with MM will have PET-avid le-sions, and heterogeneity of visual criteria and poor interobserver reproducibility can be a problem with interpretation of data from these imaging studies
As CR rates have improved, more sensitive tech-niques to measure the depth of response have been in-vestigated The sFLC ratio has been shown to have prognostic significance at the time of diagnosis[9] Us-ing this ratio to monitor disease status durUs-ing
Trang 3treatment has also been examined Singhal et al.[18]
demonstrated a high degree of discordance between
the serum IFX and the sFLC ratio Seventy-nine
per-cent of patients with a positive serum IFX had a normal
sFLC ratio, whereas only 6% of those with negative
se-rum IFX had an abnormal sFLC ratio, resulting in
a sensitivity and specificity for the sFLC ratio
com-pared with the serum IFX of 66% and 69%,
respec-tively [18] Similarly, Giarin et al [19] showed
discordance between sFLC ratios and IFX in patients
who received transplantation, although when using
a method that assesses total sFLC concentration (free
and bound), the concordance with IFX was better
De Larrea et al [20] reported that an abnormal
sFLC ratio is frequently (73% of CR patients) due to
presence of oligoclonal bands as part of normal
im-mune reconstitution after auto-PBSCT and is actually
associated with a good prognosis The major value of
sFLC assessment is in patients with light chain
only-MM, due to lack of sensitivity of electrophoretic
methods to detect sFLCs[21] Conversely, secretory
MM with fully assembled Igs may have normal sFLC
ratios in 5% of cases [22] Thus, although the sFLC
ratio is now included in the definition of sCR by the
IMWG, it remains controversial how to incorporate
sFLC measurement into minimal residual disease
monitoring in MM Similarly, other novel methods
to quantitate heavy chain Ig ratios are currently lacking
sufficient published data to support their routine use in
therapy monitoring at this time
Minimal residual disease detection by PCR
Molecular monitoring of disease by MFC and
PCR has been commonly used in chronic
myeloge-nous leukemia, acute lymphoblastic leukemia, and
acute promyelocytic leukemia to help determine
prog-nosis and guide therapy [23-25] Several PCR
techniques have been described for use in minimal
residual disease monitoring in MM Use of PCR
allows the amplification of even single cells,
providing an exquisitely sensitive method to detect
minimal residual disease However, minimal residual
disease testing in myeloma by PCR has proved
challenging for several reasons The Ig heavy and
light chain (IGH, IGK, and IGL) loci have significant
somatic hypermutation (SHM), with an average
92.2% homology to the germline sequence for IGH
sequences, 93.9% for IGK, and 93.4% for IGL [26]
For this reason, standard primers designed against
the framework regions of the Ig genes occasionally
fail to bind to the patient template DNA sufficiently
well to result in amplification As a result of SHM at
the binding sites of commercial primers, researchers
have attempted to develop highly sensitive molecular
assays for individual Ig rearrangements through the
design of allele-specific oligonucleotide (ASO)
primers, or primers based upon the patient’s individual
sequence that is a product of both the specific rear-rangement as well as any somatic hypermutation [27] PCR or even quantitative PCR can then be per-formed using these primers, allowing highly sensitive monitoring of the patient’s clone
Table 1 summarizes data available from several studies examining the role of PCR monitoring for minimal residual disease in MM Most early studies used ASO-PCR methods[28-34] However, in these studies done before the era of more effective therapy regimens, molecular minimal residual disease measurement by qualitative PCR was found not to
be useful, as nearly all patients were positive for residual disease at the molecular level aside from some molecular remissions after PBSCT An early small case series demonstrated persistent molecular remissions using qualitative, non–ASO-PCR in small numbers of patients, suggesting the possibility of cure, particularly with allogeneic SCT (allo-SCT) [35] Corradini et al.[31]described molecular remis-sion with a qualitative PCR approach using ASO primers in significantly more patients after allo-SCT compared to auto-PBSCT [31] Several studies have also demonstrated the prognostic significance of min-imal residual disease negativity by PCR after allo-SCT [32,36-38]
More recently, semi-quantitative fluorescent and real-time quantitative PCR (RQ-PCR) techniques, primarily using ASO primers, were introduced to cor-relate the level of the clone with clinical disease mani-festations and outcomes[39-43] These methods have allowed very sensitive minimal residual disease monitoring on the order of 1026 and permit trends
in levels to be followed rather than binary positive or negative results Using ASO RQ-PCR, Korthals
et al [44]showed that low minimal residual disease (\0.2% 2IgH/b-actin) measured before HDT and auto-PBSCT was significantly associated with im-proved median EFS and OS compared with high min-imal residual disease Sensitivity reached 1025in 88%
of cases in this study using Taqman technology on the LightCycler system (Roche, Mannheim, Germany) Ladetto et al [45] documented persistent molecular remissions using either qualitative nested ASO-PCR
or ASO RQ-PCR in patients with MM treated with bortezomib, thalidomide, and dexamethasone as con-solidation after auto-PBSCT, with no patient in mo-lecular remission relapsing after a median follow-up
of 42 months An update to this study showed after
a median follow-up of 65 months, a 5-year OS of 100% for patients achieving minimal residual disease negativity; no patient achieving molecular remission has died[46]
Thus, PCR is a very sensitive technique that has demonstrated prognostic significance after allo-SCT, auto-PBSCT, and after consolidation therapy with novel agents Unfortunately, ASO-PCR–based
Trang 4Table 1 Studies Examining PCR for Minimal Residual Disease Monitoring in MM
Authors No of Patients Method Sensitivity Technical Success Rate Treatment Regimen CR Minimal Residual Disease Negativity Rate
Corradini et al [28] 18 ASO nested PCR NR 83% Auto-SCT or allo-SCT 50% (6/12) 0% (0/12)
Swedin et al [30] 36 ASO semi-nested PCR 1024-1025 67% Auto-SCT or allo-SCT 42% (15/36) 21% (5/24)
Corradini et al [31] 51 ASO-PCR 1025-1026 84% Auto-SCT or allo-SCT 71% (36/51) 7% (2/27, auto-PBSCT);
50% (7/14, allo-SCT)
Martinelli et al [33] 229 ASO-PCR 1025 88% (44/50) Auto-SCT or allo-SCT Allo 5 38% (26/68)
Auto 5 22.5% (36/161)
27% (12/44)
Ladetto et al [39] 29 Real-time PCR (not ASO)
ASO nested PCR
1024
1023-1024
66%
73% (FR1/ASO) 100% (FR3/ASO)
Novella et al [43] 36 PCR (not ASO)
ASO nested PCR
1024-1026
1024-1025
Fenk et al [42] 11 ASO real-time PCR 1024-1026 NR Auto-SCT or allo-SCT 45% (5/11) 27% (3/11)
65% (39/60) >0.015%
Ladetto et al [45] 39 ASO nested
Real-time PCR (not ASO)
1026
Korthals et al [44] 70 Real-time ASO-PCR 1024-1025 76% Auto-SCT 25% nCR before auto-PBSCT
29% nCR after auto-PBSCT
17% (9/53) before auto-PBSCT 21% (8/38) after auto-PBSCT
MM indicates multiple myeloma; CR, complete response; ASO, allele-specific oligonucleotide; NR, not reported; Allo-BMT, allogeneic bone marrow transplant; Auto-SCT, autologous stem cell transplant; Allo-SCT, allogeneic stem cell transplant; Auto-PBSCT, autologous peripheral blood stem cell transplant; nCR, near complete response.
Trang 5methods require sequencing each patient’s individual
clone(s) and developing primers specific to the patient’s
rearranged and somatically mutated sequence, a process
impractical in the general clinical setting However, in
2003, the BIOMED-2 Concerted Action group
de-signed a panel of primers, which have been extensively
applied to clonality testing in a number of B cell
lym-phomas [47-49] Plasma cell neoplasms were not
included in the design or in the validation of the
primers However, in other B cell malignancies, it was
demonstrated that the use of a combination of a panel
of IGH and IGK primers could identify a clonal
rearrangement in 98% of all cases, including post–
germinal center (therefore somatically hypermutated)
B cell neoplasms such as many diffuse large B cell
lymphomas and marginal zone lymphomas [50]
Al-though plasma cell neoplasms were avoided in these
ini-tial studies due to the known complication of SHM, the
use of multiple panels of primers against numerous loci
of the Ig genes, including nonfunctional
rearrange-ments more common in myeloma, increases the
likeli-hood that at least 1 primer pair will bind and allow
amplification Subsequently, Martınez-Sanchez et al
[51] have demonstrated that a set of 4 BIOMED-2
primer pairs alone was required to detect clones in
91% of patients with myeloma using unsorted BM
aspi-rates and that molecular minimal residual disease has
prognostic value for PFS after auto-PBSCT, albeit
with lower sensitivity than ASO-PCR and MFC
Minimal residual disease detection by flow
cytometry
MFC is a technique increasingly described in the
literature as a viable method for minimal residual
dis-ease monitoring in MM, with several examples
sum-marized in Table 2 MFC can distinguish between
normal and malignant PCs by the aberrant expression
of cell surface markers in approximately 90% of
pa-tients[27] MFC has become a useful tool in MM for
a variety of reasons First, malignant PCs consistently
have aberrant immunophenotypes to distinguish them
from benign PCs Second, these immunophenotypes
are relatively stable over time, allowing for consistent
detection and quantification of the abnormal clone Third, modern MFC is sufficiently sensitive to detect
as few as 0.01% atypical plasma cells in a normal
BM [52,53] The European Myeloma Network has recommended that CD38, CD45, and CD138 be tested simultaneously in at least 1 tube and included
in all tests if possible CD19 and CD56 are the minimum recommended markers for identifying abnormal PCs (along with assessing cytoplasmick/l expression), with CD20, CD27, CD28, and CD117 preferably included to broaden applicability [54] Most of the reported studies use 4-color MFC, an older, less sensitive technique; however, 6-color and even 8-color MFC have been described[52,55,56]
In 1999, Almeida et al [57] described that MFC1 DNA ploidy using 13 different 3-color com-binations can detect residual MM cells with sensitivity
up to 1025at 3 months after auto-PBSCT Rawstron
et al.[53], using CD19 and CD56 as markers of neo-plastic PCs, demonstrated that patients with neoneo-plastic PCs at 3 months after auto-PBSCT had shorter PFS than those with only normal PCs MFC detected neo-plastic PCs in 27% of patients in IFX-negative CR, which predicted a shorter PFS OS was significantly higher in a low-risk group (normal PCs present 2 af-ter auto-PBSCT) compared with high-risk patients (100% versus 54%; P \ 0001) Liu et al [58] retrospectively demonstrated a significant PFS differ-ence in patients who, before auto-PBSCT, had
#1.8% abnormal PCs compared with patients with 1.8% abnormal PCs as measured by CD38/CD19/ CD45/CD56 expression (P5 017) No OS difference was demonstrated based on percent of PCs or achieve-ment of CR/very good partial response (VGPR) Paiva
et al [59]in a prospective analysis demonstrated by multivariate analysis that minimal residual disease sta-tus at day 100 after auto-PBSCT was the most impor-tant prognostic factor for PFS (median 71 versus 37 months; P \ 001) and OS (median not reached versus 89 months; P 5 002) in patients treated on the GEM2000 protocol When minimal residual dis-ease was examined by IFX in this study by univariate analysis, there was a significant improvement in both
Table 2 Studies Examining MFC for Minimal Residual Disease Monitoring in MM
Authors No of Patients Method Sensitivity
Technical Success Rate Treatment Regimen CR
Minimal Residual Disease Negativity Rate
CR/VGPR
8%
MFC indicates multiparameter flow cytometry; MM, multiple myeloma; CR, complete response; Auto-SCT, autologous stem cell transplant; auto-PBSCT, autologous peripheral blood stem cell transplant; NR, not reported; VGPR, very good partial response; GEM2000, alternating cycles of vincristine, car-mustine, melphalan, cyclophosphamide, prednisone (VBMCP) and vincristine, carcar-mustine, doxorubicin, dexamethasone (VBAD) followed by high-dose melphalan and auto-PBSCT.
Trang 6PFS and OS in patients with negative IFX compared
with positive IFX at day 100 after auto-PBSCT;
how-ever, this was not significant by multivariate analysis
The following 4-color Ab combinations were used
CD38 In more than 90% of cases, the CD38/CD56/
CD19/CD45 combination alone distinguished
abnor-mal MM PCs from norabnor-mal PCs Miniabnor-mal residual
dis-ease negativity was defined as \1 MM PC in 104
normal PCs (sensitivity 1024) The same group further
described the prognostic significance of the presence
or absence of specific surface markers assessed by
MFC and showed that high-risk genetic markers by
FISH and persistent minimal residual disease by
MFC at day 100 after auto-PBSCT predicted short
CR, thus identifying patients with a poor prognosis
and high risk of early progression[60,61]
Thus, it has been prospectively demonstrated that
minimal residual disease measurement by MFC is
sen-sitive and predictive of survival outcomes However,
MFC is a developing technology, with techniques still
variable among institutions and laboratories Data is
also dependent on the quality of the aspirate and can
vary considerably depending on which aspirate sample
is analyzed[40] Thus, further work needs to be done
to standardize techniques and criteria for minimal
re-sidual disease assessment by MFC in MM
Comparison Studies
PCR and MFC have been directly compared in
several small studies (Table 3) Sarasquete et al [27]
retrospectively examined minimal residual disease by
IFX, PCR, and MFC in 32 patients with MM in CR
or near CR after HDT and auto-PBSCT The ASO
RQ-PCR technique was only applicable in 75% of
pa-tients, whereas 90% of samples could be analyzed by
MFC using Ab panels described in Paiva et al [59]
In 25% of cases, PCR and MFC resulted in discordant
results In all cases, PCR was positive with negative
MFC; no cases were positive by MFC and negative
by PCR The discordance rates for either PCR or
MFC with IFX were 38%, with the more sensitive
method varying from case to case PFS was signifi-cantly longer in patients with PCR#1024, but not sig-nificantly longer in patients with negative IFX or MFC
\1024, although there was a trend toward significance with MFC Thus, in a small series of patients, minimal residual disease negativity by ASO RQ-PCR predicted longer PFS, whereas PFS was not significantly differ-ent for patidiffer-ents with negative IFX and negative MFC A second study by Lioznov et al [62] found that MFC and ASO-PCR correlated extremely well (r2 5 0.94; P \ 0001) in 69 samples, with only 1 sample unevaluable by ASO-PCR (.98% evaluable) and none unevaluable by MFC
Zhao et al [63] compared multiple methods of minimal residual disease monitoring in 121 BM sam-ples Immunohistochemistry was the most effective method for detecting residual disease, with a 96% de-tection rate, followed by limited MFC (3-color analy-sis, CD38/CD45/k, CD38/CD45/l, CD138/CD45/
k, CD138/CD45/l) at 72% Cytogenetics (15%), FISH (50%), and detection of IgG andk light chain gene rearrangements by qualitative PCR with a limited set of non-ASO primers (60%) were less successful Al-though this study is an interesting comparison of mul-tiple techniques, the sensitivity of both MFC and PCR are likely limited due to the use of older methodology Additionally, the majority of patients had residual dis-ease at the time of BM examination, and no compari-sons with serologic studies such as electrophoresis or IFX were made Paiva et al [64] compared IFX, sFLC, and immunophenotyping by MFC in 102 pa-tients.65 years of age enrolled in the GEM05 65 year trial Three 4-color combinations (CD38/
and ß2-microglobulin/CD81/CD38/CD117) were used to detect phenotypic aberrancies in PCs Seven percent of patients with no minimal residual disease
by MFC (sensitivity#1024 to 1025) after induction therapy (ie, immunophenotypic response) remained IFX positive initially, although all subsequently be-came IFX-negative Discrepant results were common among all methods tested Those patients with immu-nophenotypic response had significantly increased
Table 3 Studies Examining Multiple Methods for Minimal Residual Disease Monitoring in MM
Authors
No of Patients Methods Sensitivity
Technical Success Rate Treatment Regimen CR
Minimal Residual Disease Negativity Rate Rawstron et al [53] 45 3-color MFC
PCR (not ASO)
1024
1023-1025
100%
64%
56% (25/45) Sarasquete et al [27] 32 Real-time ASO PCR
4-color MFC
1025
1024
75%
90%
GEM2000 (auto-PBSCT) 58% 29% (7/24)
54% (13/24) Mart ınez-Sanchez et al [51] 53 Fluorescent PCR
(not ASO) 4-color MFC
1023-1024
1024
91%
94.5%
GEM2000 (auto-PBSCT) 51% 53% (28/53)
33% (17/51)
MM indicates multiple myeloma; CR, complete response; MFC, multiparameter flow cytometry; ASO, allele-specific oligonucleotide; Auto-SCT, autol-ogous stem cell transplant; NR, not reported; GEM2000, alternating cycles of vincristine, carmustine, melphalan, cyclophosphamide, prednisone (VBMCP) and vincristine, carmustine, doxorubicin, dexamethasone (VBAD) followed by high-dose melphalan and auto-PBSCT; auto-PBSCT, autologous peripheral blood stem cell transplant.
Trang 7PFS and time to progression compared to those with
CR (IFX-negative and\5% PCs on BM biopsy) or
sCR (CR and normalization of the sFLC ratio);
how-ever, no OS benefit was noted
Measurement of Minimal Residual Disease
in MM
The challenges
Measurement of minimal residual disease in MM
has been a challenging endeavor Myeloma is a
hetero-geneous disease, making disease burden difficult to
measure and follow in many circumstances Some
pa-tients present primarily with focal bone disease that is
readily seen on imaging but not easily evaluated in the
serum or by BM biopsy Others have patchy BM
in-volvement with no evidence of focal bone inin-volvement
or have evidence of diffuse marrow enhancement with
a paucity of serum and urinary paraprotein Thus,
de-pending on their disease phenotype and molecular
characteristics, certain methods of minimal residual
disease measurement may not be applicable to some
patients with myeloma, making it difficult to develop
uniform guidelines for minimal residual disease
mon-itoring in this disease
The depth and prognostic role of minimal residual
disease status after HDT/auto-PBSCT and
consolida-tion therapy in patients who have achieved CR or
VGPR after initial induction therapy is not well
de-fined Electrophoretic or sFLC ratio techniques used
to detect PC products are valuable to detect disease
when there are clear differences between monoclonal
and polyclonal Igs, but these methods do have clear
limitations After treatments that affect production of
all Igs, such as Total Therapy or auto-PBSCT,
detec-tion of residual disease by SPEP, UPEP, IFX, and
sFLC becomes less precise and complicated by limited
residual B cell repertoires, which lead to
oligoclonal-ity There have been no large randomized studies in
MM comparing different treatment strategies that
have evaluated minimal residual disease detected by
MFC or PCR using either ASO or wider panels of
con-sensus primers No studies prospectively examining
minimal residual disease using MFC or PCR have
been reported in patients treated with novel agents
with or without HDT/auto-PBSCT Thus, more
sen-sitive methods for detecting minimal residual disease
are needed to compare the depth of remission using
different treatment strategies
MFC has been slightly less sensitive than PCR[27]
These comparisons, however, are dependent upon the
specific methodologies used as well as which
combina-tions of primers (PCR) and antibodies (MFC) are used
In both cases, the patchy nature of the disease makes
false-negative results a concern New 6-color and
8-color MFC techniques have not uniformly been shown
to increase sensitivity beyond 1024but can reduce costs
and time to perform the analysis[52,55,56] However,
in the presence of background polyclonal plasma cells, MFC clearly has an advantage in the ability to identify the abnormal population without any decrement
in analytical sensitivity, while sensitivity clearly decreases in PCR-based methods unless ASO primers are used Due to the wide availability, ease, and rapid turnaround time of MFC, this is likely to become the method of choice for minimal residual disease mea-surement in MM
Timing of minimal residual disease assessment Multiple questions remain to be answered, in-cluding when is the best time to measure minimal residual disease in MM Korthals et al [44] showed that pre-auto-PBSCT minimal residual disease posi-tivity by PCR was an independent prognostic factor for both EFS and OS, with patients with low-minimal residual disease having significantly im-proved EFS and OS However, this is a retrospective study of a small number of patients treated with idar-ubicin and interferon, agents that are not commonly used since the development of new nonchemothera-peutic agents Paiva et al.[59]showed a significant in-crease in OS and PFS in patients with no minimal residual disease by MFC at day 100 after auto-PBSCT However, obsolete induction chemotherapy regimens were also used in this study Ladetto et al [45]demonstrated the value of minimal residual dis-ease measurement by PCR after auto-PBSCT and consolidation therapy with bortezomib and thalido-mide This study also included induction chemother-apy (vincristine, doxorubicin, and dexamethasone) with agents that are now uncommonly used It thus remains unclear when is the best time to integrate minimal residual disease measurement into therapeu-tic decision making
Several important questions remain unanswered based on the current literature Should only patients who are positive for minimal residual disease receive HDT/auto-PBSCT, and can minimal residual disease measurement be used to help determine whether this therapy should be administered early or later in a pa-tient’s treatment course? Recent data suggests that
OS is equivalent for early versus delayed auto-PBSCT after induction therapy with immunomodula-tory agents; however, minimal residual disease measurement could help to identify patients that could benefit more from 1 of these strategies[65] Based on minimal residual disease measurement, should some patients receive consolidation therapy while others should not? Can minimal residual disease monitoring
be used to determine the need for or duration of main-tenance therapy? When is the best time after auto-PBSCT to measure minimal residual disease? Prospective clinical studies are needed to address these and other unanswered management dilemmas
Trang 8To examine prospectively the prognostic
signifi-cance of minimal residual disease monitoring by
MFC, we are currently conducting a prospective study
of newly diagnosed patients with MM Patients who
meet criteria for MM and who are candidates for
auto-PBSCT are treated with either bortezomib,
lena-lidomide, and low-dose dexamethasone (VRD) or
bor-tezomib, liposomal doxorubicin, and low-dose
dexamethasone (VDD) for 4 cycles, followed by
auto-PBSCT in those patients experiencing a partial
response or greater MFC using three 7-color tubes
is performed on the initial pretherapy marrow aspirate
to determine the aberrant immunophenotypes of the
MM cells In patients achieving$VGPR after 4 cycles
of induction therapy, minimal residual disease is being
assessed before and at 3 months after auto-PBSCT
The aims of the study are to assess the frequency of
minimal residual disease negativity at the end of 4
cy-cles of VRD or VDD and to assess the frequency of
minimal residual disease negativity at the end of
auto-PBSCT compared to before auto-PBSCT If
current novel regimens like VRD or VDD achieve
a high incidence of minimal residual
disease-negativity, it may be reasonable to delay or not offer
HDT/auto-PBSCT in first remission and to proceed
with consolidation and/or maintenance therapy
The goal: Risk adapted therapy
Many techniques are available for the
measure-ment of disease burden in MM Improving therapies
leading to increased CR rates have made prolonged
minimal residual disease-negative states achievable
even without allo-SCT Radiographic studies, such
as PET imaging, as well as examination of the serum
and BM using highly sensitive techniques, such as
PCR and MFC, are valuable tools for measurement
of minimal residual disease in MM Investigation of
minimal residual disease by PCR techniques in BM
of patients with MM achieving CR after
auto-PBSCT provides relevant information on residual
tumor load with a significant impact on the risk of
re-lapse However, other minimal residual disease
tech-niques, such as MFC, yield similar prognostic
information with the advantage of being easier, faster,
and more widely available Thus, it is reasonable to
think that MFC will become the routine technique
for assessing minimal residual disease in MM in
clini-cal practice However, to reach this goal, additional
studies including larger numbers of patients and
lon-ger follow-up are required At the moment, evidence
indicates that RQ-PCR and MFC are complementary
techniques in minimal residual disease evaluation for
MM Both techniques show that decreases in the BM
tumor load below 1 malignant cell per 10,000 total
BM cells could be used as a target for the definition
of a molecular/immunophenotypic CR
Minimal residual disease measurement by PCR and MFC seems to have prognostic value in MM; how-ever, barriers to the uniform adoption of these tech-niques remain due to the heterogeneity of the disease, lack of availability of testing, and the relative novelty of agents that commonly lead to durable CRs
in patients with MM A pragmatic approach to cus-tomizing disease management should include accu-rately defining disease phenotypes as well as proper risk stratification using validated pretreatment disease prognostic factors and posttherapy disease monitor-ing An individualized minimal residual disease moni-toring algorithm based on individual disease genetic signature and pretreatment phenotype for each patient with MM, with a goal to help predict outcome and guide therapeutic decisions, will enable a risk-adapted approach to disease management More clini-cal trials integrating these approaches are needed to determine how best to use improved disease monitor-ing methods and develop a truly personalized ap-proach to MM therapy
ACKNOWLEDGMENT Financial disclosure: The authors have nothing to disclose
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