Positron emission tomography/computed tomography in the management of Hodgkin and B-cell non-Hodgkin lymphoma: An update

¹⁸ F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) is now an integral part of lymphoma staging and management. Because of its greater accuracy compared with CT alone, PET/CT is currently routinely performed for staging and for response assessment at the end of treatment in the vast majority of FDG-avid lymphomas and is the cornerstone of response classification for these lymphomas according to the Lugano classification. Interim PET/CT, typically performed after 2 to 4 of 6 to 8 chemotherapy/chemoimmunotherapy cycles with or without radiation, is commonly performed for prognostication and potential treatment escalation or de-escalation early in the course of therapy, a concept known as response-adapted or risk-adapted treatment. Quantitative PET is an area of growing interest. Metrics, such as the standardized uptake value, changes (Δ) in the standardized uptake value, metabolic tumor volume, and total lesion glycolysis, are being investigated as more reproducible and potentially more accurate predictors of response and prognosis. Despite the progress made in standardizing the use of PET/CT in lymphoma, challenges remain, particularly with respect to its limited positive predictive value, emphasizing the need for more specific molecular probes. This review highlights the most relevant applications of PET/CT in Hodgkin and B-cell non-Hodgkin lymphoma, its strengths and limitations, as well as recent efforts at implementing PET/CT-based metrics as promising tools for precision medicine.

Response Assessment Criteria and Their Applications in Lymphoma: Part 1

The effectiveness of cancer therapy, both in individual patients and across populations, requires a systematic and reproducible method for evaluating response to treatment. Early efforts to meet this need resulted in the creation of numerous guidelines for quantifying posttherapy changes in disease extent, both anatomically and metabolically. Over the past few years, criteria for disease response classification have been developed for specific cancer histologies. To date, the spectrum of disease broadly referred to as lymphoma is perhaps the most common for which disease response classification is used. This review article provides an overview of the existing response assessment criteria for lymphoma and highlights their respective methodologies and validities. Concerns over the technical complexity and arbitrary thresholds of many of these criteria, which have impeded the long-standing endeavor of standardizing response assessment, are also discussed.

Comparison of various criteria in interpreting end of therapy F-18 labeled fluorodeoxyglucose positron emission tomography/computed tomography in patients with aggressive non-Hodgkin lymphoma

Various interpretation criteria exist to assess end of therapy F-18 labeled fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) in lymphoma. This study was carried out to compare these criteria. Data of 69 patients with aggressive non-Hodgkin lymphoma (AGR-NHL) who underwent FDG PET/CT at the end of therapy and were followed up for a minimum period of 1 year (median follow-up period 17 months) were evaluated. Twenty-eight of the 69 patients were found to have residual/recurrent disease during follow-up. The accuracy for predicting residual disease of International Harmonization Project (IHP) criteria, London criteria and Gallamini criteria was 71.0%, 84.0% and 88.4%, respectively. Gallamini and London criteria had greater accuracies in predicting residual disease than IHP criteria (p = 0.0001). The major difference in accuracy was due to the low positive predictive value of IHP criteria. Positive predictive values (PPVs) of both London and Gallamini criteria (79.3% and 88.5%, respectively) were high when compared with that of IHP criteria (60.5%) (p = 0.001). Negative predictive values (NPVs) were similar for all the criteria. In conclusion, Gallamini and London criteria had higher accuracy when interpreting end of therapy FDG PET/CT studies in AGR-NHL. London criteria can be used preferentially over Gallamini criteria because of simplicity in interpretation and reproducibility.

My treatment approach to patients with diffuse large B-cell lymphoma

My favored treatment approach for patients with diffuse large B-cell lymphoma continues to evolve. Diffuse large B-cell lymphoma can now be cured in more than 50% of patients. This is a result of improved definitions of the disease, improved diagnostic capabilities, better staging and restaging techniques, a useful prognostic index to guide therapeutic decisions, and the development of increasingly effective therapies. Positron emission tomographic scans have improved the accuracy of both staging and restaging. Findings on a positron emission tomographic scan at the end of therapy are the best predictors of a good treatment outcome. Numerous subtypes of diffuse large B-cell lymphoma have been identified that require specific treatment approaches. For example, plasmablastic lymphoma typically lacks CD20 and does not benefit from treatment with rituximab. Diffuse large B-cell lymphoma originating in specific extranodal sites such as the central nervous system, testes, and skin presents special problems and requires specific treatment approaches. A subgroup of diffuse large B-cell lymphoma with a very high proliferative rate seems to have a poor outcome when treated with CHOP-R and does better with regimens used for patients with Burkitt lymphoma. New insights into the biology of these disorders are likely to further change treatment approaches. Recognition that diffuse large B-cell lymphoma is not one disease, but a variety of clinicopathologic syndromes provides the opportunity to further improve our ability to benefit patients.

Impact of FDG-PET/CT in the management of lymphoma

Since the introduction of (67)Gallium-citrate 30 years ago, nuclear medicine has played an important role in the evaluation of malignant lymphoma. During that time, several radiotracers were evaluated as potential alternatives for the diagnosis of lymphoma, but the introduction of (18)F-fluorodeoxyglucose PET (FDG-PET) marked a major turning point. FDG-PET took over most of the role of gallium, and is now an essential tool in the diagnosis of lymphoma. FDG-PET is increasingly being used for assessment of the tumor staging prior to treatment, for evaluating the response to treatment, and for monitoring the early reactions to therapy to predict the final outcome. FDG-PET has been shown to have more accurate diagnostic capability than conventional CT and MRI for distinguishing the tumor necrosis and residual masses frequently seen after therapy in lymphoma patients without any clinical and biochemical manifestation. Malignant lymphoma is the first disease for which FDG-PET was adopted as a tool for response assessment in the international standard criteria. However, lymphoma does not always display a clear high uptake, and there are some pitfalls in assessing the response to therapy. This review will highlight the most important applications of FDG-PET in lymphoma, focusing on the advantages and pitfalls of this imaging, and past and ongoing efforts to standardize the use of FDG-PET, particularly in response to assessment and therapy monitoring.

Granulocyte-macrophage colony stimulating factor-induced immune priming of cyclophosphamide, doxorubicin, vincristine, and prednisone with rituximab chemoimmunotherapy in previously untreated patients with diffuse large B-cell lymphoma and mantle cell lymphoma

Granulocyte-macrophage colony stimulating factor (GM-CSF) has been shown to enhance CD20 antigen expression, augment antibody-dependent cell-mediated cytotoxicity, and stimulate immune cell proliferation. This may lead to an improved anti-tumor effect of rituximab while reducing the severity of chemotherapy-induced myelosuppression. We evaluated the safety and efficacy of cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) in sequential combination with GM-CSF priming and rituximab in previously untreated patients (n = 39) with diffuse-large B-cell lymphoma (DLBCL) and mantle cell lymphoma (MCL). CHOP was administered every 21 days on day 1, GM-CSF 250 μg/m(2)/day on days 9 through 15, and rituximab 375 mg/m(2) on day 15 of each cycle. The overall response rate was 87%, with complete response in 64%. At a median follow-up of 84.3 months, the overall and progression-free survival rates were 54% and 49%, respectively. The most common toxicity was myelosuppression. Sequential combination of CHOP with GM-CSF priming and rituximab was feasible and effective, warranting further evaluation.

FDG-PET/CT in lymphoma

Molecular Imaging has played a prominent role in the assessment of lymphoma for now almost three decades since the introduction of (67)Ga-citrate imaging for staging and restaging of both Hodgkin's and non-Hodgkin's lymphoma (HL and NHL). Since then other molecular probes have been investigated for more accurate pre- and posttreatment assessment of lymphomas but none of these probes was widely accepted and utilized until the emergence of (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET). FDG-PET or FDG-PET/CT, which combines FDG-PET with CT scanning, is now widely utilized for response assessment of lymphoma after completion of therapy, for pretreatment staging, and, increasingly, also for assessment of response during therapy (therapy monitoring). Particularly for response assessment at therapy conclusion, FDG-PET has been shown to be considerably more accurate than CT or conventional MRI because of its ability to distinguish between viable tumor and necrosis or fibrosis in posttherapy residual mass (es) that are frequently present in patients with lymphoma without any other clinical or biochemical evidence of disease. FDG-PET/CT is therefore the noninvasive modality of choice for response classifications of HL and aggressive NHLs consistent with the recently revised, primarily FDG-PET/CT-based, response criteria for lymphoma. This review will highlight the most important applications of FDG-PET (FDG-PET/CT) in lymphoma emphasizing the strengths and pitfalls of this imaging approach, past and ongoing efforts to standardize the use of FDG-PET, particularly in response assessment and therapy monitoring. Other promising molecular probes for lymphoma imaging will also be briefly discussed.

Clinical utility of PET/CT in lymphoma

OBJECTIVE

The purpose of this review is to assist interpreting radiologists in becoming familiar with the role of PET/CT in baseline staging and therapeutic response assessment in the management of lymphoma, in becoming aware of imaging pitfalls, and in understanding the natural behavior of lymphoma and the therapeutic options.

CONCLUSION

Therapeutic strategies for the management of lymphoma are constantly being refined to improve long-term survival with the lowest risk of toxicity to the patient. PET/CT is accurate for baseline staging and yields important prognostic information for determining the most appropriate initial treatment. Used for evaluation of treatment response, PET/CT can depict residual viable malignant lesions with greater accuracy than can other imaging techniques. The findings thereby influence decisions about the need for additional or alternative treatment.

PET imaging in lymphoma

PET has become a cornerstone procedure in modern lymphoma management. This paper reviews, from a clinical point of view, the evidence for using PET in the different subtypes of lymphoma and the different steps of their management. The reader is given an overview of the current PET-based interventional lymphoma trials and an insight into possible future developments in the field, including new PET tracers.

FDG-PET Evaluation of Response to Treatment

This article discusses evaluating response after and during therapy in various settings and for the types of cancers for which ample evidence demonstrates that PET imaging with flourodeoxyglucose provides a valuable surrogate for response to therapy. It also briefly discusses pitfalls in obtaining an optimal assessment of response and issues that need further attention for this modality to become established as an independent predictor of response to anticancer therapy.

18F-FDG PET for posttherapy assessment of Hodgkin's disease and aggressive Non-Hodgkin's lymphoma: a systematic review

Although studies have shown that (18)F-FDG PET, when used to assess the response of malignant lymphoma after treatment, has a strong ability to predict relapse, its diagnostic accuracy in clinical practice remains unclear. The aim of this study was to systematically review the diagnostic accuracy of (18)F-FDG PET in detecting residual disease at the completion of first-line therapy of Hodgkin's disease (HD) and aggressive non-Hodgkin's lymphoma (NHL).

METHODS

We searched relevant articles from 1966 to July 2006 using MEDLINE, EMBASE, SCOPUS, Biological Abstracts, bibliographies, review articles, and textbooks without language restriction. One assessor (for non-English-language studies) or 2 assessors (for English-language studies) independently reviewed each article to abstract relevant study characteristics and results. Relevant individual patient data or subgroup data were provided by the investigators if they were unavailable from the publications. We estimated summary receiver operating characteristic curves and confidence regions for summary sensitivity and specificity.

RESULTS

Nineteen studies consisting of 474 HD and 254 aggressive NHL patients were included. These studies had heterogeneity and suboptimal methodologic quality and reporting. Reported ranges for the sensitivity and specificity of (18)F-FDG PET in predicting disease relapse were 0.50-1.00 and 0.67-1.00, respectively, for HD and 0.33-0.77 and 0.82-1.00, respectively, for NHL. These estimates were similar when conventional imaging tests showed a residual mass. For HD studies, the summary receiver operating characteristic curves were similar irrespective of whether a residual mass was detected by conventional tests. Factors explaining the variability of diagnostic estimates were not identified.

CONCLUSION

Although currently available evidence is still limited, (18)F-FDG PET seems to have good diagnostic accuracy for assessing residual HD at the completion of first-line treatment. Clinical data on this use of (18)F-FDG PET for aggressive NHL are more limited. Prospective studies with a more rigorous research design, conduct, and reporting would more reliably reveal the clinical diagnostic accuracy of this imaging modality.

PET/CT: form and function

Functional imaging with positron emission tomography (PET) is playing an increasingly important role in the diagnosis and staging of malignant disease, image-guided therapy planning, and treatment monitoring. PET with the labeled glucose analogue fluorine 18 fluorodeoxyglucose (FDG) is a relatively recent addition to the medical technology for imaging of cancer, and FDG PET complements the more conventional anatomic imaging modalities of computed tomography (CT) and magnetic resonance imaging. CT is complementary in the sense that it provides accurate localization of organs and lesions, while PET maps both normal and abnormal tissue function. When combined, the two modalities can help both identify and localize functional abnormalities. Attempts to align CT and PET data sets with fusion software are generally successful in the brain; other areas of the body is more challenging, owing to the increased number of degrees of freedom between the two data sets. These challenges have recently been addressed by the introduction of the combined PET/CT scanner, a hardware-oriented approach to image fusion. With such a device, accurately registered anatomic and functional images can be acquired for each patient in a single scanning session. Currently, over 800 combined PET/CT scanners are installed in medical institutions worldwide, many of them for the diagnosis and staging of malignant disease and increasingly for monitoring of the response to therapy. This review will describe some of the most recent technologic developments in PET/CT instrumentation and the clinical indications for which combined PET/CT has been shown to be more useful than PET and CT performed separately.

Use of 18F-FDG positron emission tomography following allogeneic transplantation to guide adoptive immunotherapy with donor lymphocyte infusions

Fluorine-18 fluorodeoxyglucose positron emission tomography ((18)F-FDG PET) provides valuable prognostic information in the management of lymphoma patients. However, the utility of (18)F-FDG PET following allografting is unclear. We analysed the use of (18)F-FDG PET after allogeneic reduced-intensity transplantation (RIT) performed in our institution. Between June 1998 and January 2002, 55 patients underwent RIT for either Hodgkin or non-Hodgkin lymphoma. At least one (18)F-FDG PET scan was performed during the post-transplant period (median five studies) in 15 (27.2%) of these 55 patients. PET scans were performed after re-staging computed tomography (CT) and were categorised depending on (18)F-FDG uptake. The first PET scan was informative in 11 of 15 patients (73%) and influenced the administration of donor lymphocyte infusions (DLI) in nine: leading to earlier DLI administration in two patients, earlier dose escalation in one, withholding of DLI administration in five and dose reduction in one. In addition, subsequent monitoring with (18)F-FDG PET scans documented a graft-versus-lymphoma effect in five patients (median post-DLI follow-up 33 months, range 13-36 months). These preliminary data suggest that (18)F-FDG PET has a role in guiding DLI administration and monitoring the immunotherapeutic effect in patients after allogeneic transplantation. This retrospective pilot study forms the basis for a prospective study to clarify the utility of (18)F-FDG PET/CT in these patients.

FDG-PET in the clinical management of Hodgkin lymphoma

Positron emission tomography (PET) is a molecular functional imaging technique that provides qualitative and quantitative information about the localization and activity of pathophysiological processes. The most commonly used tracer for oncological purposes is 2-[18F]fluoro-2-deoxy-d-glucose (FDG). FDG-PET has within recent years become the most important nuclear medicine imaging modality in the management of lymphoma. This review summarizes the data published so far concerning the value of FDG-PET in staging, treatment monitoring, therapy planning, and follow-up of Hodgkin lymphoma (HL). FDG-PET detects more disease sites and involved organs than conventional staging procedures including computerized tomography (CT) and has a large influence on staging. FDG-PET during and after therapy appears to provide considerable prognostic information. However, the impact on patient outcome is not clear since no controlled trials are conducted and follow-up periods are generally short. The value of dual-modality PET/CT and its potential role in the radiotherapy planning is discussed.

Diffuse large cell lymphoma

A review of new or emerging ideas concerning diffuse large B-cell lymphomas is presented, with particular emphasis on histologic classification, genetic prognostic factors, first-line and salvage treatments, and specific locations such as neurologic, cutaneous, or gastrointestinal sites. This lymphoma remains the most heterogeneous of all lymphomas for its clinical characteristics and outcome. This heterogeneity is probably secondary to the fact that a large proportion of lymphomas seems to occur from a transformation of an unknown indolent lymphoma.

Radionuclide evaluation of patients with lymphoma

Nuclear medicine imaging techniques allow us to peer into physiologic processes, avoiding the need to wait until anatomic changes are detectable, and allowing for prompt, informed management decisions. Recognition of normal, abnormal, and post-therapy scan patterns is critical to achieve the necessary sensitivity and specificity needed for patient management. Gallium scintigraphy using updated techniques has an important continuing role in management of patients with lymphoma. Gallium scintigraphy can contribute to patient management primarily by detecting residual disease or relapse after treatment, monitoring response during therapy, and providing prognostic information. FDG and PET cameras, especially dedicated ring systems, offer high resolution and high-contrast images, thereby demonstrating additional sites of disease. Although preliminary evidence looks promising that FDG can provide all information that Ga-67 has been shown to do in the past, additional data are required. Further studies will show whether FDG-PET can provide prognostic information and predict disease-free and overall survival, the availability of both FDG and PET scanners, and issues of cost. Patient accessibility will undoubtedly also play a role in when, or whether, FDG-PET will totally replace Ga-67 scintigraphy in the management of patients with lymphoma.

Positron emission tomography and gallium metabolic imaging in lymphoma

Metabolic imaging allows the recognition of active tumor mass because of its fixed tracer. For patients with Hodgkin's disease and non-Hodgkin lymphoma, (67)gallium and (18)fluorodeoxyglucose (FDG) have been employed. This review describes the role of (67)gallium scintigraphy (Ga-scan) and positron emission tomography (PET) in the staging and follow-up of patients with lymphoma. These tools do not appear to be more powerful than conventional imaging for initial staging and treatment choice. Ga-scan is only valid for thoracic examination. PET imaging following treatment resolves the problem of persisting images on CT scan; nearly all patients with FDG uptake have an early relapse. Whether this examination will allow for intensified treatment and possible cure of more patients is yet to be demonstrated.

18-FDG-PET as a prognostic indicator in the treatment of aggressive Non-Hodgkin's Lymphoma-comparison with CT

Less than 50% of newly diagnosed patients with aggressive histology Non-Hodgkin's Lymphoma (NHL) are cured with standard treatment. The ability to accurately monitor response to treatment is crucial in order to select out patients who need more intensive or salvage treatment. This study assesses the accuracy of FDG-PET as compared to CT in remission assessment following treatment of aggressive NHL, and its value in estimating relapse-free survival. It also evaluates the prognostic value of early interim PET scan in prediction of treatment outcome. Forty-nine adult patients with biopsy-proven aggressive NHL between September 1993 and December 1997 were included. All patients had pre-treatment FDG-PET demonstrating increased uptake in sites of disease. Forty-five patients had a post-treatment PET to assess remission status and 4 had an interim but not a post-treatment PET. Thirty-three of these patients also had a pre- and a post-treatment CT scan. Twenty-three of the 49 patients had an interim PET during chemotherapy to assess early response. PET and CT scan results were correlated with relapse data to examine their accuracy in remission assessment and prediction of prognosis. The median follow-up duration is 30 months. Overall the result of post-treatment PET scan appears to predict disease outcome, with relapse rates of 100% (9/9) and 17% (6/36) for positive and negative PET respectively [p<0.001]. In a subgroup of 33 patients, direct comparison of post-treatment PET and CT shows that PET was more accurate than CT in assessing remission status following treatment. Relapse rate was 100% for positive PET and only 18% for negative PET (p<0.001), compared to 41% and 25% for patients with positive and negative CT respectively (p>0.1). PET was particularly useful in assessment of residual masses seen on CT scan. The interim PET provided valuable information regarding early assessment of response and long-term prognosis, with no relapses in patients with no or minimal residual uptake compared to 87.5% relapse rate in patients with persistent PET activity (p<0.001). FDG-PET is an accurate method of assessing remission and estimating prognosis following treatment of aggressive NHL, with positive and negative predictive accuracies of 100% and 82% respectively. PET is more accurate than CT in assessing remission and prediction of relapse-free survival. An interim PET scan after 2-3 cycles of chemotherapy predicts the long-term outcome early-on and has a high negative predictive value (100%). This may assist to separate at an early stage good-prognosis patients who are likely to be cured with standard chemotherapy from those patients with poorer prognosis who require alternative treatment.