Lymphoma imaging: nuclear medicine

Managing lymphoma with non-FDG radiotracers: current clinical and preclinical applications

Nuclear medicine imaging modalities such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT) have played a prominent role in lymphoma management. PET with [(18)F]Fluoro-2-deoxy-D-glucose (FDG) is the most commonly used tool for lymphoma imaging. However, FDG-PET has several limitations that give the false positive or false negative diagnosis of lymphoma. Therefore, development of new radiotracers with higher sensitivity, specificity, and different uptake mechanism is in great demand in the management of lymphoma. This paper reviews non-FDG radiopharmaceuticals that have been applied for PET and SPECT imaging in patients with different types of lymphoma, with attention to diagnosis, staging, therapy response assessment, and surveillance for disease relapse. In addition, we introduce three radiolabeled anti-CD20 antibodies for radioimmunotherapy, which is another important arm for lymphoma treatment and management. Finally, the relatively promising radiotracers that are currently under preclinical development are also discussed in this paper.

A 18F-FDG-positive, 67Ga-negative, and transferrin receptor expression-negative patient with diffuse large B-cell lymphoma

We recently experienced a case with uveitis suffering from fever of unknown origin suspected of being caused by sarcoidosis. Chest computed tomography showed right supraclavicular, bilateral mediastinal, and right hilar lymphadenopathy, and intensive abnormal uptake of 2-[18F]fluoro-2-deoxy-D-glucose (18F-FDG) was observed on positron emission tomography with 18F-FDG (FDG-PET). On the other hand, 67Ga scintigraphy showed almost no abnormal findings. Histopathological examination revealed the lesion to be a diffuse large B-cell lymphoma (DLBCL), namely, an aggressive non-Hodgkin lymphoma from a right supraclavicular lymph node biopsy specimen. Additional immunohistochemical analysis showed the negative expression of transferrin receptor (TfR) on the formalin-fixed paraffin-embedded specimen. Although DLBCL is generally considered to be a 67Ga-avid tumor, it does not always have a large number of TfRs and that leads to a discrepancy between the 67Ga scintigraphy and FDG-PET findings. FDG-PET should be more appropriate for the initial staging of DLBCL than 67Ga scintigraphy, whereas 67Ga scintigraphy might be able to provide additional information including prognostic factors and to support strategies that target TfR for cancer therapy.

[Positron emission tomography in internal medicine]

FDG-PET is now an established diagnostic tool in oncology. Fluorodeoxyglucose is not a specific tracer for malignant lesions but rather for elevated glucose metabolism, present not only in cancer but also in inflammatory and infectious lesions. FDG-PET has thus been suggested for diagnosis of fevers of unknown origin, deep bone or visceral infectious foci, inflammatory vasculitis or sarcoidosis and unknown primary tumors, all frequent situation in internal medicine. The main characteristics of FDG-PET are its ability to rule out focal inflammation or infection with a high degree of certainty when the examination is negative because of its good negative predictive value and its usefulness as an early marker of therapeutic response, compared with anatomy-based or conventional scintigraphic imaging. Large-scale prospective studies are necessary, however, before FDG-PET is integrated into routine clinical use. It should be compared with different techniques already validated (biology, radiology, conventional scintigraphic imaging) and its cost-effectiveness should be evaluated.