Research Article
Utility of positron emission tomography scans in mantle cell lymphoma
Peter J. Hosein,1 Vitor H. Pastorini,1 Fabio M. Paes,2 Daryl Eber,2 Jennifer R. Chapman,3
Aldo N. Serafini,2 Ash A. Alizadeh,4 and Izidore S. Lossos1,5
Positron emission tomography (PET) scans are widely used in patients with lymphoma but little is known
about their utility in mantle cell lymphoma (MCL). MCL patients were included from two prospective trials
and one observational study at our institution. A total of 276 PET scans were performed among 52 patients.
After a median follow-up of 37.5 months, the 3-year event-free survival (EFS) and overall survival (OS) were
73% (95% confidence interval [CI]: 61–85%) and 92% (95% CI 85–100%), respectively. There were 34 pretreatment PET scans, 26 interim, 28 end-of-treatment, 162 surveillance, and 26 scans at relapse or beyond. Pretreatment PETs were positive in 94%. A negative interim or end-of-therapy PET scan was not significantly
associated with better EFS or OS, but no deaths were observed in patients who had a negative interim or
end-of-therapy PET. Surveillance PET scans had a high false positive rate (35%) and low positive predictive
value (8%). PET scans contributed to an earlier diagnosis of relapse in only two out of the 18 patients (11%)
who relapsed. PET scans did not meaningfully contribute to staging or surveillance of MCL patients in this
study. There was a trend toward improved survival in patients who had a negative end-of-therapy PET scan.
C 2011 Wiley-Liss, Inc.
Am. J. Hematol. 86:841–845, 2011. V
Introduction
Mantle cell lymphoma (MCL) is a distinct subtype of nonHodgkin lymphoma (NHL) accounting for 6–8% of the estimated 65,540 new NHL cases in the United States annually [1]. MCL was previously considered to be an indolent
incurable lymphoma, but the elucidation of some key molecular features of this disease has led to a better understanding of its biology and consequently a more refined
approach to treatment. The molecular hallmark of MCL is
the t(11;14) translocation, which results in cyclin D1 overexpression and consequently increased cell proliferation [2–
4]. The high proliferation rate of MCL cells may contribute
to disease aggressiveness and inferior clinical outcomes
[5,6]. Indeed, many investigators have now adopted very
aggressive treatment paradigms including intensive chemoimmunotherapy [7,8] as well as upfront myeloablative therapy and autologous stem cell transplant [9–11] in an
attempt to improve survival outcomes. Although these
approaches have led to better outcomes [12], relapses are
still common, necessitating further research into innovative
management approaches. Moreover, there appears to be a
subset of MCL patients who follow a more indolent course
[13] and better identification of these patients may help to
streamline management algorithms. The propensity of MCL
to exhibit a pattern of continuous relapses over time implies
that after frontline therapy, patients have residual disease
that is below the level of detection of conventional diagnostic tools. It is not uncommon to find subcentimeter lymph
nodes on a computed tomography (CT) scan at the end of
treatment for lymphoma and these would not be considered
significant by CT size criteria. Functional or metabolic
imaging with 18Fluorine-fluorodeoxyglucose positron emission tomography (18F-FDG PET) scanning can potentially
identify lesions that contain residual disease that would not
be diagnosed by conventional imaging. Based on data supporting this premise, PET scans are now routinely recommended as part of the post-therapy evaluation of patients
with HL and aggressive NHL such as diffuse large B-cell
lymphoma (DLBCL) [14,15]. The incorporation of PET
scans into the clinical management of MCL has not been
studied systematically. The initial reports describing the
FDG-avidity of NHLs focused mainly on the more common
aggressive subtypes such as DLBCL and only included a
handful of MCL patients [16–18], with the largest reported
NHL PET series of 766 patients containing only 14 MCL
patients [19]. Recently, there have been a few retrospective
series of MCL patients who underwent PET scanning
throughout their disease course [20–23]. One consistent
theme through these reports is that MCL appears to be
almost uniformly FDG-avid before treatment but PET scans
are not sufficiently sensitive to pick up disease in the gastrointestinal tract or the bone marrow, both of which are
common sites of involvement for MCL. Because of the paucity of available data, we undertook this study to evaluate
the clinical utility of PET scans in MCL
Patients and Methods
Study design. Patients were eligible for inclusion in this study if
they were enrolled in one of the prospective MCL trials at the University
of Miami Sylvester Comprehensive Cancer Center or Jackson Memorial
Hospital, both in Miami, FL. Patients were also included from an observational NHL study database that stores clinical, pathological, and outcome data for patients treated off-protocol at the same institutions
listed above. One of the prospective therapeutic trials, the UM-MCL1
(registered at www.clinicaltrials.gov with the national clinical trial [NCT]
identifier NCT00450801) accrued between 2004 and 2008 and has
been published,8 and the other UM-MCL2 is ongoing (NCT00878254).
1
Department of Medicine, Division of Hematology/Oncology, University of
Miami Miller School of Medicine, Sylvester Comprehensive Cancer Center,
Miami, Florida; 2Department of Radiology, Division of Nuclear Medicine, University of Miami Miller School of Medicine, Sylvester Comprehensive Cancer
Center, Miami, Florida; 3Department of Pathology, University of Miami Miller
School of Medicine, Sylvester Comprehensive Cancer Center, Miami, Florida; 4Department of Medicine, Divisions of Oncology and of Hematology,
Stanford University School of Medicine, Stanford, California; 5Department of
Molecular and Cellular Pharmacology, University of Miami Miller School of
Medicine, Sylvester Comprehensive Cancer Center, Miami, Florida
Conflict of interest: Nothing to report.
Contract grant sponsor: National Institutes of Health; Contract grant numbers: CA109335, CA122105.
Contract grant sponsors: Fidelity Foundation and the Dwoskin Family Foundation (to I.S.L.).
*Correspondence to: Izidore S. Lossos, Sylvester Comprehensive Cancer
Center, 1475 NW 12th Avenue (D8-4), Miami, FL 33136.
E-mail: Ilossos@med.miami.edu
Received for publication 10 May 2011; Revised 22 June 2011; Accepted 24
June 2011
Am. J. Hematol. 86:841–845, 2011.
Published online 8 July 2011 in Wiley Online Library (wileyonlinelibrary.com).
DOI: 10.1002/ajh.22126
C 2011 Wiley-Liss, Inc.
V
American Journal of Hematology
841
http://wileyonlinelibrary.com/cgi-bin/jhome/35105
research article
The eligibility criteria for both of these studies were identical and have
been described elsewhere [8]. In brief, untreated patients with a confirmed histological diagnosis of MCL underwent baseline evaluation
with laboratory tests, CT and PET (or combined PET/CT), esophagogastroduodenoscopy, colonoscopy, and bone marrow biopsy. When
possible, immunostaining with an antibody to Ki-67 (DAKO, Carpinteria,
CA) was quantified in the diagnostic specimens. Treatment consisted of
two cycles of intensive chemoimmunotherapy and then patients underwent interim reimaging with CT and PET (or combined PET/CT).
Regardless of the result of the interim restaging, patients underwent
two more cycles of intensive chemoimmunotherapy and then had endof-therapy reimaging with CT and PET (or combined PET/CT). PET
scans were optional in the UM-MCL1 study but were required in the
UM-MCL2 study. Patients with bone marrow and/or gastrointestinal
involvement at baseline were required to have a repeat bone marrow
examination and/or endoscopy, respectively, to evaluate response to
treatment. Patients achieving a complete response (CR) to therapy
then went on to receive maintenance therapy. During the maintenance
phase, surveillance imaging with CT and PET (or combined PET/CT)
was repeated every 6 months for 3 years, or sooner if clinically indicated. The UM-MCL1 trial tested thalidomide as the maintenance
agent, and the UM-MCL2 trial is testing rituximab maintenance.
Patients with a confirmed histological diagnosis of MCL who were not
willing or eligible for participation in either of these two therapeutic trials
were followed on an observational study looking at clinical and pathological predictors of outcome in patients with NHL. All these studies
were conducted in compliance with the Declaration of Helsinki and the
Guidelines of Good Clinical Practice. The University of Miami Institutional Review Board (IRB) approved each of the protocols and all
patients participating in the therapeutic trials provided written informed
consent; the requirement for written informed consent was waived by
the IRB for patients on the observational study.
PET Imaging. All patients enrolled prior to March 2005 at the University of Miami Sylvester Comprehensive Cancer Center were studied
using the Philips C-PET System (n 5 6 scans); from March 2005 until
March 2008, a Philips Gemini Power-16 PET/CT scanner (n 5 117);
and after April 2008, Philips Gemini TF-16 and Philips Gemini TF-64
PET/CT scanners (n 5 131). Patients enrolled at the Jackson Memorial
Hospital were studied using the Philips C-PET system (n 5 18), and
GE Discovery LightSpeed system (n 5 4). Patients fasted for at least 6
hr before the 18F-FDG injection. The serum glucose level was determined at the time of 18F-FDG injection using a glucometer, and all the
patients had to have glucose levels less than 130 mg/dl. Sixty to ninety
minutes after intravenous administration of 18F-FDG (0.045 mCi/kg with
a maximum of 6 mCi for C-PET unit and 0.14 mCi/kg with a maximum
of 15 mCi for the PET/CT units), a PET or PET/CT imaging study from
the skull base to the upper thigh was acquired. Images were reconstructed by iterative algorithm (ordered subset expectation maximization) with and without attenuation correction. A clinical report was
issued at the time of performance of each scan. For the purposes of
this study, all PET scan images and reports were reviewed again by
one nuclear medicine specialist physician to ensure consistency of
interpretation and reporting of results. Pretreatment PET scans were
interpreted as being either negative or positive for disease activity. A
positive scan was defined as one having higher FDG uptake relative to
uptake in the mediastinal blood pool or surrounding background, with
no similar activity seen on the contralateral side, or increased activity
at any location incompatible with normal physiological distribution [24].
A negative scan was defined as having no abnormally increased FDG
accumulation at any site. Metabolic activity within sites of pathological
FDG uptake was semiquantitatively analyzed. A region of interest was
manually positioned over the pathological focus with maximal standardized uptake value (SUVmax). The SUVmax was calculated using measured activity, decay-corrected injected dose, and patient body weight.
For interim restaging or end-of-therapy scans, responses were determined according to the International Harmonization Project (IHP) criteria [14]. Interim response assessment by PET was performed at least 2
weeks after chemotherapy (4 weeks after the last dose of rituximab)
and end-of-therapy PET scans, at least 3 weeks after chemotherapy (5
weeks after the last dose of rituximab).
Statistical analysis. Event-free survival (EFS) was calculated from
the date of the start of frontline therapy to the date of first appearance
of progressive disease, relapse, or death from any cause. Patients,
known to be alive and without progressive disease, were censored at
the time of last contact. Overall survival (OS) was calculated from the
date of the start of frontline therapy to the date of death from any
cause or last contact. EFS and OS were estimated by the Kaplan-Meier
842
TABLE I. Patient Characteristics (N 5 52)
Age
Median (range)
Sex
Male
Female
ECOG performance status
0
1
2
Extranodal sites
Bone marrow or leukemic phase
Gastrointestinal tract
Spleen
Lung or pleura
Orbital, ocular, or central nervous system
Other
Ann Arbor stage
II
III
IVA
IVB
Histology
Diffuse
Blastic
Beta-2 microglobulin
<3 mg/dl
3 mg/dl
Missing
Ki-67 staining
10%
11–29%
30%
Missing
Mantle Cell International Prognostic Index
Low (<5.7)
Intermediate (5.7 and <6.2)
High (6.2)
Missing
Frontline treatment
Ritxumab 1 MACLO-IVAM
Rituximab 1 CHOP
Rituximab 1 Hyper-CVAD/MA
Rituximab 1 Bendamustine
Other
Best response to frontline treatment
Complete response
Partial response
Stable disease
Progression or death
Missing
Number of PET scans performed
Pretreatment/baseline
Interim during frontline treatment
End of frontline treatment
Surveillance
At first relapse or beyond
Total
58 years (39–92)
40 (77%)
12 (23%)
31 (60%)
18 (35%)
3 (6%)
42
16
12
9
3
13
(81%)
(31%)
(23%)
(17%)
(6%)
(25%)
2
8
27
15
(4%)
(15%)
(52%)
(29%)
44 (85%)
8 (15%)
20 (38%)
20 (38%)
12 (23%)
5
12
18
17
(10%)
(23%)
(35%)
(33%)
19
18
7
8
(37%)
(35%)
(13%)
(15%)
29
12
3
2
5
(56%)
(23%)
(6%)
(4%)
(10%)
36
8
1
3
4
(69%)
(15%)
(2%)
(6%)
(8%)
34
26
28
162
26
276
Abbreviations—CHOP: cyclophosphamide, doxorubicin, vincristine, prednisone;
Hyper-CVAD/MA: hyperfractionated cyclcophosphamide, vincristine, doxorubicin,
dexamethasone alternating with methotrexate and cytarabine; MACLO-IVAM:
methotrexate, leucovorin, doxorubicin, cyclophosphophamide, vincristine alternating with ifosphamide, mesna, etoposide, and cytarabine.
method with corresponding two-sided 95% confidence interval (CIs) for
survival proportions based on Greenwood’s variance and the log-transform method [25]. The statistical software package PASW Statistics 18
(IBM Corporation, New York, NY) was used for these analyses.
Results
Between November 2004 and March 2011, 52 patients
with MCL were treated at our institutions and had a total of
276 PET or combined PET/CT scans performed (median 4,
range 1–15). Among these patients, 22 were treated on the
UM-MCL1 protocol (between 2004 and 2008), seven on the
UM-MCL2 protocol (between 2008 and 2011), and 23 were
enrolled on the observational NHL study (between 2004
and 2011). Among the patients on the observational study,
only two had initial ‘‘watchful waiting’’ for 6 months and 9
years, respectively, and the remainder had treatment
American Journal of Hematology
research article
Figure 1.
Kaplan-Meier survival plots showing EFS (panel A) and OS (panel B) stratified by the MIPI group (low, intermediate, and high) in all 52 patients.
started soon after the initial diagnosis. The median followup for all patients was 37.5 months (range 0.1–173.7
months). The median follow-up for the patients on the UMMCL1 and UM-MCL-2 protocols was 51.1 months (range
0.5–81) and 12.9 months (range 4.6–21.7), respectively. All
29 of these patients had longitudinal follow-up from the
time of their initial diagnosis until death or March 2011. The
baseline characteristics of the patients are shown in Table
I. Patients who were treated on the study protocols had a
significantly longer EFS compared with those treated offprotocol (median 54.1 vs. 35.6 months, log rank P 5
0.022). The OS was not significantly different for patients
treated on-protocol versus off-protocol (median not reached
vs. 64.2 months, log rank P 5 0.15), likely due to the small
number of deaths in both groups. The baseline MCL International Prognostic Index (MIPI) score [26] was predictive
of OS but not EFS in the entire study population (log rank
P for a difference between MIPI groups 5 0.013 and 0.078,
respectively), as shown in Fig. 1.
Pretreatment PET scans
PET scans prior to administration of any therapy were
available in 34 patients and demonstrated abnormal signal in
32 (94%; exact 95% CI 80–99%) patients. In the initial staging workup, 26 of 34 patients had stage IV disease by virtue
of a positive bone marrow biopsy and three of these 26
patients had significant FDG accumulation in the bone marrow, giving a sensitivity of PET of 12% (95% CI 2–30%) for
the detection of bone marrow involvement. Within this subgroup of 34 patients with pretreatment PET scans available,
10 had biopsy-proven gastrointestinal tract involvement by
MCL. Only two of these patients had abnormal FDG accumulation in the gastrointestinal tract, giving a sensitivity of
20% (95% CI 3–56%) for the detection of gastrointestinal
involvement. Among the patients with stage I–III disease by
conventional staging, PET scanning upstaged one patient
with previously unsuspected splenic involvement, increasing
the stage from III to IIIs by the Ann Arbor system. Therefore,
PET upstaged 4% (95% CI 0–20%) of patients in this study.
A comparison of negative versus positive baseline PET
scans was not done as only two out of these 34 patients
had completely negative pretreatment PET scans.
Interim PET scans
PET scans during the course of frontline therapy were
available in 26 patients. Most of these patients (69%) were
enrolled on the UM-MCL1 or UM-MCL2 trials and had the
interim scan done after two cycles of therapy. There was
no significant difference in survival between patients who
had a negative interim PET scan (i.e., CR by the IHP criteria) compared to those with a positive interim PET scan, as
shown in Table II.
End-of-therapy PET scans
PET scans at the end of frontline therapy were available
in 28 patients, with 14 being positive and among these, further workup confirmed persistence of lymphoma in only one
case. In the remaining 13 patients, five were later proven to
have relapsed lymphoma after a median disease-free interval
of 9 months (range 6.3–48.8 months). There was a trend toward better survival for patients who had a negative end-oftherapy PET (i.e., CR by the IHP criteria) compared to those
with a positive PET but the difference was not statistically
significant, as shown in Table II and Fig. 2.
Surveillance PET scans
A total of 162 surveillance PET scans were performed
among 34 patients who were in remission and asymptomatic from a disease standpoint at the time of the scans.
These scans yielded five true positive results, 56 false positives, one false negative, and 100 true negatives. Among
TABLE II. Survival by Interim and End-of-treatment PET Scan Resulta
All patients (N 5 52)
Interim PET (N 5 26)
Negative (N 5 15)
Positive (N 5 11)
End-of-treatment PET (N 5 28)
Negative (N 5 15)
Positive (N 5 13)
3-year EFS (95% CI)
3-year OS (95% CI)
Median follow-up (range)
73% (61–85%)
92% (85–100%)
37.5 months (0.1–173.7)
80% (60–100%)
82% (59–100%)
p 5 0.73
100% (94–100%)
91% (74–100%)
p 5 0.19
32.5 months (4.1–76.7)
87% (69–100%)
69% (44–94%)
p 5 0.16
100% (94–100%)
85% (65–100%)
p 5 0.07
44.2 months (4.6–76.7)
CI: confidence interval; EFS: event-free survival; OS: overall survival; PET: positron emission tomography.
a
Statistics not calculated for pretreatment PET scans as there were only two negative scans among 34 patients.
American Journal of Hematology
843
research article
Figure 2.
Kaplan-Meier survival plots showing EFS (panel A) and overall survival (OS, panel B) stratified by the end-of-treatment positron emission tomography scan.
the 56 false positive scans, three were serial scans done
for the same patient who was later diagnosed with thyroid
cancer in the FDG-avid site, two were serial scans in the
same patient who was later diagnosed with lung cancer at
the FDG-avid site, and one represented renal cancer. The
most frequent sites of false-positive FDG update were cervical lymph nodes (63%), mediastinal lymph nodes (34%),
abdominal lymph nodes (20%), and bone (14%). The two
patients with negative pretreatment PET scans were not
included in the interim or end-of-therapy analyses. They
were included in the surveillance analysis where they contributed 11 of the 162 PET scans (7%) analyzed. Among
these 11 scans, there was one true positive and 10 true
negatives. The sensitivity (Sens), specificity (Spec), positive
predictive value (PPV), and negative predictive value (NPV)
for surveillance PET scans for the detection of relapsed
MCL were 83% (95% CI 36–100%), 64% (95% CI 56–
72%), 8% (95% CI 3–18%), and 99% (95% CI 95–100%),
respectively. For detection of any malignancy (including
MCL), the Sens, Spec, PPV, and NPV were 91% (95% CI
59–100%), 66% (95% CI 58–74%), 16% (95% CI 8–28%)
and 99% (95% CI 95–100%), respectively. None of the
patients with false positive PET scans during surveillance
were in the cohort of patients who were treated with rituximab maintenance.
PET scans at relapse
There were 18 patients in the study who achieved a CR
with frontline therapy but then went on to have a biopsyproven relapse. These 18 cases were examined to determine whether PET scans contributed to the diagnosis of
relapse. In 12 of these patients, relapse was suspected
by a new symptom or physical examination finding, most
commonly being the development of a new enlarged
lymph node mass. The remaining six patients were clinically asymptomatic and abnormal surveillance PET/CT
scans raised the suspicion for relapse. In three of the six
cases, an abnormality was detected on both the PET and
CT portions of the study; in the fourth case, there was an
abnormality on CT but not PET; in the fifth case,
increased FDG accumulation at the site of relapse preceded the appearance of enlarged lymph nodes by 3
months; and in the last case, increased FDG accumulation in the duodenum (with no CT abnormality) prompted
a biopsy leading to the diagnosis of relapse. Therefore,
abnormal FDG accumulation was the exclusive first sign
of relapse in only two out of the 18 patients (11%, 95%
CI 1–35%) who relapsed.
844
Discussion
PET scans are increasingly being used in oncology and
especially in lymphoma. A recent analysis of Medicare beneficiaries in the US showed a 39% increase in the use of
PET scans in lymphoma between 1999 and 2006 [27].
Consensus guidelines now include recommendations for
initial and post-treatment PET scans in aggressive NHL
[14], and risk-adapted strategies based on interim PET
scan results are currently being tested [15]. MCL is a relatively uncommon subtype of NHL and no specific guidelines
exist for the use of PET in MCL.
Our study represents one of the largest series examining
the utility of PET scans in MCL patients. For pretreatment
PET scans, our data are consistent with other published
series in that MCL is almost always FDG-avid at presentation [21]. Our finding that pretreatment PET scans had a
low sensitivity (12%) to detect bone marrow involvement is
also consistent with the reports by Bodet-Milin et al. and
Brepoels et al. who reported sensitivities of 12% and 13%,
respectively [21,22]. Similarly, we found a sensitivity of 20%
for gastrointestinal tract involvement in our study, which
was not markedly different to the sensitivity of 11%
reported by Bodet-Milin et al. [22].
As most patients had positive scans at the time of the diagnosis, we could not stratify patients by a categorical positive versus negative PET scan and therefore we considered
using a continuous variable such as SUVmax. Other investigators have reported that a higher SUVmax at baseline is
associated with worse survival [22,23]. In these reports,
the cutoff SUVmax values that stratified patients into high
risk versus low risk groups were 5 and 6, respectively. This
variation may be due to differences in the study populations as well as different types of scanners and image acquisition techniques. In our study, the scans were performed on five different machines over a 6-year period. It
has been well described that several technical, biological,
and physical factors affect the reproducibility of FDG quantification [28]. Therefore, we could not reliably analyze
SUVmax as a prognostic variable in our study. Recently, there
have been efforts to standardize SUV measurements to
reduce variability and allow comparisons across different
machines [29]. We plan to use these techniques prospectively
to further study SUVmax as a prognostic variable in MCL.
With regards to PET for response assessment, a CR on
an interim PET did not correlate with better survival in our
study. The evidence for interim PET scanning as a predictive tool in NHL is inconsistent, and a recent review reported
a sensitivity of interim PET for DLBCL of 33–100% and a
American Journal of Hematology
research article
specificity of 53–100% [15]. This wide range for the sensitivity
and specificity was due to a lack of uniformity in the timing
of the scans, interpretation of the scans, and study endpoints. In recent reports, the PPV of PET in studies using
rituximab has fallen to as low as 42% in one series [30],
and this has been hypothesized to be due to inflammatory
changes associated with the recruitment of immune cells to
the tumor by rituximab [31].
For end-of-therapy assessment, we found that a posttreatment CR defined by the IHP criteria (which includes a
negative PET), did not predict for better survival in our
study, although there was a trend in that direction. In a similar analysis, Bodet-Milin et al. [22] reported a statistically
significant survival advantage for patients with a CR (i.e.,
negative PET) compared to those without a CR. This discrepancy between Bodet-Milin’s results and ours may have
been due to a lower statistical power in our study (28 vs.
36 patients) or the higher number of events in our study
due to a longer median follow-up (44 vs. 21 months). A
consistent finding in that study and ours was that a negative end-of-therapy PET scan had a high NPV for relapse
(100% and 87%, respectively) and death (100% in both
studies). Of note in our study, a positive end-of-therapy
PET scan was only acted on in one patient with proven
persistent lymphoma. The others with positive end-of-therapy scans were followed until relapse was proven before
any further treatment was given.
The majority of PET scans analyzed in this study (59%)
were performed for routine surveillance of asymptomatic
patients who were in remission from MCL. A total of 35%
of these scans yielded false positive results, giving a PPV
of only 8%. None of these false positives occurred in
patients who were receiving rituximab maintenance. An examination of the patients who relapsed revealed that
among the 34 patients who had at least one surveillance
PET scan, only two (6%) had an abnormality on PET that
was the exclusive first sign of relapse. Therefore, almost all
the relapses could have been diagnosed by history, physical examination, and CT scans. These data argue against
the use of PET scans for surveillance of asymptomatic
patients who are in remission from MCL. El-Galaly et al.
recently reported their experience with surveillance PET/CT
scans in patients with aggressive NHL, showing that the
impact of PET/CT was limited by the high number of false
positives, and was significantly more costly than CT surveillance [32]. Although we did not gather minimal residual disease data in our study, there is emerging evidence that this
may be a more promising tool for surveillance in MCL [33].
In summary, this study does not support routine use of
PET scans in MCL for staging or surveillance. There appears
to be consistent data that a CR by the IHP response criteria,
which includes a negative PET scan, is a good prognostic
factor and this can form the basis of future studies testing
risk-adapted approaches after front-line therapy.
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