129IN - Potential and Pitfalls in Pet-Imaging of Lymphoma

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ABSTRACT PET-CT has become a pivotal tool for staging patients with lymphomas and the PET response adapted treatment is emerging as a rational therapeutic approach. The improved sensitivity and spatial resolution due to technical innovations increased the performance of the last generation PET-CT systems particularly in the detection rate of the small lesions with low metabolic rate. This may change the role of the screening with 18F-fluoro-deoxy-glucose (FDG) PET-CT in the staging and clinical management of the very indolent lymphomas, classified, so far, as FDG-non avid in which the use of the PET-CT is not yet recommended. Moreover the increased sensitivity will allow to reduce the quantity of radiotracer injected and, therefore, the patient radiation exposure. A risk-adapted therapy requires early prognostic indicators. There is increasing evidence of the potential prognostic value of quantitative parameters obtained from initial staging FDG PET-CT in patients with high-grade lymphomas. In addition to the standardized uptake value (SUV), more recently, new parameters, the metabolic tumor volume (MTV) and total lesion glycolysis (TLG), appeared of particular interest as a prognostic pointer in DLBCL and PMBCL. A significant amount of false positive findings in PET imaging is due to the FDG uptake by inflammatory cells that leads to an overestimation of the viable tumor cell fraction, particularly after immunochemotherapy or radiotherapy. For these reasons, 18F-fluorothymidine (FLT), a biomarker for proliferative activity, is intensively studied as a valid alternative for FDG to predict therapy response: initial promising results have been obtained in MCL, DLBCL and FL. Infections due to neutropenia are not uncommon after chemotherapy and to distinguish between reactive lymphadenopathy and residual or relapsed disease is sometimes very challenging, particularly in patients with HIV-associated lymphoma. Though the quantitative PET metrics may help the qualitative analysis, a correct interpretation of PET findings can only be made in the context of the overall patient's clinical and laboratory data. In exceptionally difficult cases, short-term follow-up may be helpful and when treatment decision includes aggressive options, a biopsy of PET-positive lesions may be required. Disclosure: The author has declared no conflicts of interest.