Role of initial, interim, and post-treatment F-18 FDG PET/CT in prognostication of clinically diagnosed extranodal lymphoma

Objectives FDG PET/CT has well documented prognostic values for evaluation of diffuse large B cell lymphoma but the role in evaluation of extranodal lymphoma is still vague. In the present study we evaluated the diagnostic performance of initial, interim, and post-treatment FDG PET/CT in extranodal lymphoma.

Methods In this retrospective study we evaluated thirty patients (8 females and 22 males; age range 12 -80 years; mean age 47.8 years) of untreated and newly diagnosed extranodal lymphoma. All the patients included in this study had undergone PET/CT studies at various interval (for initial staging, interim PET after 4 cycles of chemotherapy and post treatment PET). The PET/CT scans were analyzed by two experienced nuclear medicine physician. Any abnormal uptake in iPET (interim) and post therapy PET scan evaluated in accordance with Deauville’s criteria (Five point Scoring system). The results were noted either PET negative (Deauville score 1-3) or PET positive (Deauville score > 4). End point was negative post therapy PET (Deauville score 1), imaging and clinical follow up. FDG uptake (SUVmax values) in the lesions was calculated in all the three PET scans (initial, Interim and post therapy).

Results Of the total thirty patient, 9 patients had primary intestinal lymphoma, 3 lungs, 3 tonsils , 2 skin, 2 brain, 2 testicular, 2 bone, 2 salivary gland, 2 pancreas, 2 adrenal and one nasopharyngeal lymphoma. Pre-treatment PET/CT identified primary extranodal disease in 13 patients and additional lymph nodal involvement in 17 patients. Interim PET scan results were negative for 19 patients and positive for 11 patients. At the end of therapy, 2/11 patients were in complete remission and 1 patient had stable disease, 6 had partial metabolic response, 2 progressive metabolic disease and one had stable metabolic disease and were considered for second-line therapy. On further analysis we also found that initial PET SUVmax had no correlation with the response to chemotherapy at interim PET (P=0.2903) and final outcome (P=0.8013). However, SUVmax of interim PET and post treatment PET are significant predictors of final outcome and overall PFS (P<0.0001).

Conclusions Interim PET and post treatment PET can predict the unfavorable outcome following treatment and help in timely planning for salvage therapy, but initial PET had little value in predicting the final outcome.