Impact of FDG-PET Imaging Versus Conventional Staging Modalities on Staging and Treatment Decisions in Large B-Cell, Follicular, and Hodgkin’s Lymphomas.

Clinical staging of lymphomas has a critical role in determining appropriate therapy and in therapeutic response assessment. While anatomic imaging by CT or MRI, together with physical examination and bone marrow biopsy (conventional staging modalities or CSM), have historically provided the basis for staging and response assessment, positron emission tomography using 18-fluoro-2-deoxyglucose (FDG-PET) has increasingly been employed in the management of patients (pts) with lymphomas. Studies comparing FDG-PET with anatomic imaging have generally found that FDG-PET identifies more sites of disease; however, the impact of FDG-PET imaging on assignment of clinical stage and treatment decisions is unclear. We retrospectively examined the impact of FDG-PET imaging on assignment of disease stage and treatment decisions compared with CSM alone in 91 pts with large B-cell lymphoma (LBCL; n=30), follicular lymphoma (FL; n=29) and Hodgkin’s lymphoma (HL; n=32). 25/30 LBCL (83%), 26/32 HD (81%) and 17/29 FL pts (59%) were evaluated at initial diagnosis by FDG-PET imaging and CSM, while others were evaluated during subsequent relapse. FDG-PET and CSM defined the same stage in 69/91 pts (76%). Stage assignment was most concordant in LBCL with only 5/30 (17%) of cases having different stages, while stage assignments were discrepant in 7/32 (22%) of cases of HL and in 10/29 (34%) of cases of FL. Of the 22 pts with discrepant results, FDG-PET resulted in upstaging of disease in 11 pts and downstaging in 11 pts. Independent confirmatory tests resolving the discrepancy were obtained in 3 of 11 pts upstaged (27%) and 7 of 11 pts downstaged by FDG-PET (64%). Abnormal FDG uptake in lymph nodes accounted for all cases upstaged by FDG-PET in which no confirmatory test was available (8/8 pts). Among 10 cases resolved by biopsy, discrepant sites included bone marrow (n = 4), bone (n = 1), pelvic or abdominal structures (n = 3), and lymph nodes (n = 2). FDG-PET results were true positive in 2/10, true negative in 1/10, false positive in 1/10, and false negative in 6/10 cases (including 4 cases with BM involvement). Incorporation of FDG-PET led to treatment changes in a minority of patients (2%). We conclude that FDG-PET is an efficient single imaging modality in pts with LBCL, FL and HL, providing information complementary to CSM. However, changes in treatment based on FDG-PET results are rare. Discrepancies between FDG-PET and CSM should be resolved by biopsy when feasible, particularly in cases in which treatment would be altered.