Departments of 1 Radiation Oncology and 2 Nuclear Medicine, Memorial Sloan-Kettering Cancer Center, New York, NY, USA
* Correspondence to: Dr J. Yahalom, Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10 021, USA. Tel: +1-212-639-5999; Fax: +1-212-639-7742; Email: yahalomj{at}mskcc.org
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Abstract |
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Patients and methods: A database of 175 patients with histologically-confirmed diagnoses of extranodal MZL was reviewed. Forty-two patients who had had FDG-PET scans for initial staging were identified. All information was obtained by retrospective review of medical records and PET scans.
Results: Thirty-four (81%) patients had focal tracer uptake within verified tumor sites, six (14%) patients did not, and two (5%) patients had indeterminate uptake. Seven of the 34 (21%) patients with uptake within verified tumor sites had uptake in regional lymph nodes and four patients were upstaged due to FDG-PET findings. Eight patients also obtained post-treatment FDG-PET scans. In five of those eight, the repeated FDG-PET scan indicated a complete response, and in three there was an indeterminate or mixed response.
Conclusion: FDG-PET scans carried out for initial staging of extranodal MZL detected disease in a high proportion of patients. This study suggests that imaging with FDG-PET scans is useful for both initial staging and follow-up of patients with extranodal MZL.
Key words: MALT lymphoma, PET scan
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Introduction |
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Extranodal marginal zone lymphoma (MZL), also known as mucosal associated lymphoid tissue (MALT) lymphoma, is the third most common NHL following only DLBCL and follicular lymphoma in incidence and it comprises approximately 8% of all NHL [7]. As with other NHL, the optimal treatment of MALT lymphomas depends on the stage of disease [8
10
]. Understanding the potential contribution of FDG-PET imaging to accurate staging and treatment response evaluation will be helpful in the management of these patients. Further, since most patients with localized disease are effectively treated with involved-field radiotherapy, the accuracy in defining the disease treatment volume can be enhanced by additional imaging information [11
].
Many reports show a correlation between high FDG uptake and high histologic grade of lymphoma [12]. Other studies report that although low-grade NHLs do not demonstrate FDG avidity to the same degree that high-grade lymphomas do, they are still FDG avid enough to demonstrate disease [13
, 14
]. Although there is evidence that FDG-PET scanning detects disease accurately in some low grade histologies such as follicular lymphoma and mantle cell lymphoma [4
], a few studies with limited numbers of patients report that FDG-PET imaging is unreliable for extranodal MALT lymphomas [15
, 16
]. However, our experience at Memorial Sloan-Kettering Cancer Center (MSKCC) suggests otherwise. Thus, we analyzed our patients with MALT lymphoma who had undergone FDG-PET imaging as part of their initial evaluation and present our results here.
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Patients and methods |
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The patients who had their FDG-PET imaging carried out at MSKCC fasted for 6 h before an injection of intravenous 18-FDG. The injections were given 60 min before images were acquired on a LSO Siemens Biograph PET/CT Scanner or on a GE Discovery LS PET/CT Scanner. Following a low-dose CT scan, multiple PET images were obtained from multiple bed positions from the level of the skull base to the pelvic floor. Iterative image reconstruction was used and attenuation corrected images were evaluated. Scans were considered positive if there was abnormal focal FDG uptake above that of background uptake. Quantification of the abnormal foci was obtained using the Standardized Uptake Value (SUV) normalized to body weight as follows: SUV=(FDG concentration in the lesion)/(injected FDG normalized to body weight). The PET images were compared with CT images for anatomic location.
Although the technology employed at the outside centers was varied, 14 of the 18 reports from outside centers indicated that attenuation correction techniques were used to evaluate the images.
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Results |
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The six patients with negative scans had the following stage distribution, I (5), and recurrent (1). The two patients with indeterminate scans had stage I disease (bladder) and stage IV disease, respectively. The patient with stage IV disease initially presented with symptoms related to her biopsy proven base of skull MALT lymphoma. MRI of the skull and CT scanning of the chest, abdomen and pelvis revealed her base of skull to be the only site of involvement. However, as previously mentioned, her FDG-PET scan (which was indeterminate for her base of skull involvement) revealed FDG avidity in her sacrum which was then biopsied revealing DLBCL.
Of the 34 patients with positive scans, the following primary sites were involved: lung (11), gastric (6), orbit (4), oral cavity (2), subcutaneous tissue (4), parotid (1), skin (1), pleura (1), retroperitoneum and flank (1), kidney and perinephric region (1), temporal region (1), and nasopharynx (1).
Of the six patients with negative scans, the following sites were involved: gastric (4), and orbit (2). The two patients with indeterminate scans had bladder and base of skull involvement as previously mentioned.
Of the 34 patients with positive FDG-PET scans, 28 patients had adequate follow-up information for analysis. Three others were still undergoing treatment, and three were only seen for initial evaluation and staging at MSKCC. At a median follow-up of 13 months, 13 patients were NED, 11 had persistent or progressive disease at their initial site of disease, two developed a new site of MALT lymphoma, one patient died of his disease, and one patient developed a new cancer (non-lymphomatous). The patient who died of his disease had extensive lung and nodal involvement with significant pulmonary compromise. He had been treated with multiple chemotherapeutic regimens with minimal response and then was treated emergently with radiation therapy (RT) for worsening pulmonary function. He deceased of pulmonary complications before finishing his RT.
Of the six patients with negative initial FDG-PET scans, all were NED at a median follow-up of 12.5 months. The patient with an indeterminate scan due to bladder involvement was NED 16 months after completion of radiation therapy. The other patient with an indeterminate scan due to base of skull involvement was NED 7 months after treatment with chemotherapy (CTX) and RT. This patient was treated with CTX in addition to RT to her base of skull (her initial site of MALT lymphoma) and her sacrum which had transformed disease (DLBCL) revealed on her staging FDG-PET scan.
Eight patients who initially had positive FDG-PET scans obtained post-treatment FDG-PET scans. Post-treatment scans were ordered at the treating physician's discretion and likely were not ordered routinely as the role of FDG-PET is still not clearly defined for this population. Three of these patients with post-treatment scans initially had a single site of disease (stage I), were treated with RT alone, and attained a complete response clinical and radiographic with negative follow-up FDG-PET scans. Figure 1 illustrates an example of a patient with stage I disease involving the orbit who had a complete response on a follow-up FDG-PET scan 4 months after the completion of RT. One patient had MALT lymphoma of his nasopharynx and was upstaged from a stage I to stage II after his initial staging FDG-PET scan revealed FDG avidity in regional lymph nodes. He was treated with RT alone to his nasopharynx and regional nodes and attained a complete response on a follow-up FDG-PET scan 3 months after the completion of RT which is illustrated in Figure 2. One patient with stage IV disease was treated with RT to her orbit with resolution of FDG uptake in the region treated on a post-treatment FDG-PET scan. One patient with stage IV disease was treated with CTX and had a mixed response on a post-treatment FDG-PET scan.
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Discussion |
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Thus far, other than a few case reports of MALT lymphoma with focal tracer uptake on FDG-PET imaging [17, 18
], the information on FDG-PET in MALT lymphomas has been limited to small series reporting poor or no uptake in the site(s) of involvement. In 1999, Hoffmann et al. published their findings from a prospective observational study of 10 patients with MALT lymphoma who underwent FDG-PET scanning and reported no focal tracer uptake in any of the 10 patients [15
]. In 2003, Hoffmann et al. published their findings from a series of 21 patients with marginal zone lymphoma, 14 of 21 had extranodal marginal zone lymphoma of the MALT type. Once again, they reported that none of the 14 patients with MALT lymphoma had focal tracer uptake in their respective tumor sites upon evaluation with FDG-PET scans [16
]. In 2003, Elstrom et al. reported on the utility of FDG-PET scanning in all non-Hodgkin's lymphomas [4
]. In her series of 172 cases, 12 were marginal zone lymphomas, 67% of which had positive PET scan results. However, the study does not document details of these cases or whether these cases were nodal or extranodal marginal zone lymphomas of the MALT type. Thus Elstrom's study neither supports nor refutes previously published studies.
In our series of 42 patients with MALT lymphoma, we found FDG-PET to be a valuable imaging and possibly valuable staging tool. In 34 of 42 patients, there was FDG avidity representing MALT lymphoma. Our data demonstrate that MALT lymphoma can be detected with FDG-PET imaging in the majority of patients (81% of patients with histologically confirmed sites of MALT lymphoma).
Only six patients in our series did not have uptake in pathologically confirmed sites of disease. Two of these cases involved the orbit, and one of those patients had had his lesion 80% excised (as per the surgeon's report) before her FDG-PET scan. Thus the remaining disease volume in this patient's orbit may have been too small to detect by PET scanning even if it was FDG avid. The other patient with MALT lymphoma of the orbit and a negative FDG-PET scan had his scan carried out at an outside center and did not provide us with a copy of the exam for review.
The remaining four cases of MALT lymphoma and negative FDG-PET scans all had gastric involvement. The lack of FDG uptake may be due to small volume disease in these patients as gastric MALT lymphomas often present with multifocal areas of limited involvement. Yet, 60% (6 of 10) of our PET-studied gastric cases had positive FDG uptake. Although the two negative series published by Hoffman et al. [15, 16
] have gastric MALT lymphomas representing the majority of their cases, it still does not fully explain their PET negative results. Another possible explanation for the negative orbit and gastric cases is that the orbit region and stomach both have normal increased glucose uptake which may decrease the accuracy of PET scans at these sites.
Another possible explanation as to why all of the patients in the two Hoffman et al. series had negative scans is because of different technical approaches. In those series, attenuation correction of the images was done only when abnormalities were seen in the uncorrected whole body images. Thus lesions with low SUV may have been missed in the uncorrected images, especially over the variable background FDG uptake in the normal stomach. At our center, attenuation correction of PET images is routinely carried out, resulting in higher tumor to background ratios of deep lesions. The two Hoffman series also used older technology and cameras that likely did not have the same resolution as newer cameras such as the ones used at our center.
Of interest, our series of 42 patients includes a disproportionately large number of patients (11) with MALT involving the lung who had FDG-PET scans. In our database of 175 patients with MALT lymphoma, only 19 had lung as their primary site of involvement, yet 11 of those patients had FDG-PET scans as part of their workup. This disproportion may be attributed to those patients being evaluated by a thoracic surgeon or pulmonologist who likely have a lower threshold for ordering FDG-PET scans as FDG-PET scans are part of the standard workup for lung cancer [1921
]. The fact that all of our cases of lung MALT lymphoma who had FDG-PET scans had focal FDG uptake in their lungs is important to note as MALT lymphoma is the most common primary lymphoma of the lung [22
, 23
]. This information may be useful for radiologists who are considering the differential diagnoses of a patient with focal FDG uptake in the lung.
Of our 42 MALT patients who initially were evaluated with FDG-PET imaging, patients with positive scans were more likely to have higher stage disease than patients with negative scans. In fact, of the 34 patients with positive scans, three were upstaged following their FDG-PET scans, and one patient with an indeterminate scan was upstaged when she was found to have a site of transformation to DLBCL that had been unidentified on prior imaging with CT.
Although the patients with negative FDG-PET scans appear to have better outcome on follow-up analysis, no conclusions can be determined from this study regarding FDG uptake and outcome of MALT lymphoma patients as there may be confounding by stage and site of disease differences in this study. Further analysis with a larger cohort of patients is necessary to determine whether or not there is a relationship between FDG uptake and outcome in MALT lymphomas.
There were several limitations to this study. One limitation is that 18 patients had their FDG-PET scans carried out at outside centers and only five patients provided their images for review at our center thus limiting our ability to completely assess the validity of those studies. Of the 13 patients who provided only reports, 11 (85%) had positive studies, and two had negative studies which is a similar percentage of positive studies found in the patients who had their studies carried out at MSKCC [18 of 24 patients (75%) who had scans at MSKCC had positive studies]. Furthermore, because these 18 studies were carried out at outside centers, there was variation in imaging techniques compromising predictive value. Another limitation to this study is that only eight patients had post-treatment FDG-PET scans to evaluate their response to treatment. This limits our ability to analyze the predictive value of the post-treatment FDG-PET findings.
Despite these limitations, this study demonstrates that FDG-PET scans are useful for staging and treatment design for patients with extranodal MALT lymphomas. As FDG-PET imaging technology advances and spreads, its role in cancer evaluation undoubtedly will expand. Our study demonstrates that MALT lymphoma is one of the cancers that can benefit from this expansion as FDG-PET imaging may lead to more accurate staging and better management. Since early stage patients or patients with symptomatic sites of MALT lymphomas are most effectively treated with RT, the information that FDG-PET scans yield in confirming localized disease is invaluable. In particular, accurate imaging information is useful for the radiation oncologist in order to design appropriate treatment fields [24].
Furthermore, our study demonstrates that FDG-PET findings that were not appreciated on CT scanning may not only upstage patients, but also may identify sites of transformation to more aggressive disease that require a different treatment approach. Future prospective studies are warranted to clarify the contribution of FDG-PET imaging to the staging and follow-up of patients with MALT lymphoma and consider incorporation of PET imaging into the lymphoma staging system.
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Acknowledgements |
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Received for publication August 9, 2004. Revision received October 26, 2004. Accepted for publication October 29, 2004.
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