Graham, Michael M.

Abstract Background: CT imaging has routinely been used for assessing therapy response in most malignancies including Non-Hodgkins Lymphoma (NHL). The presence of residual tumor is generally categorized using the International Workshop Criteria from CT imaging and bone marrow biopsies for assessing response after treatment. CT imaging has limitations in assessment of response to therapy in NHL with false positive results due to residual masses having viable tumor cells in less than 20% and the remainder being fibrosis or necrosis. In addition false negative CT results are seen due to viable tumor cells in nodes measuring less than 1.5 cm in size. F-18 FDG PET scans provide metabolic imaging of viable tumor cells due to uptake and retention of F-18 fluorodeoxyglucose preferentially in malignant cells. Method: Forty-eight patients with aggressive NHL having completed anthracycline-based chemotherapy had the post therapy FDG PET scans and CT scans reviewed by experienced readers blinded from the comparison scan and from the clinical history. PET scans were read as positive or negative for abnormal FDG consistent with residual viable tumor and the CT was read as positive or negative for nodes greater than 1.5 cm in diameter. Records were reviewed for tumor histology and evidence of tumor relapse with a median follow-up of 35 months. Results: The FDG PET and CT imaging prediction of PFS at 2 years had positive predictive values of 67% and 38%, negative predictive values of 88% and 78%, and accuracy of 81% and 50% respectively. The sensitivity and specificity of the FDG PET scan was 71% and 82% for predicting disease progression within 2 years from beginning treatment. Conclusion: FDG PET imaging was compared with CT imaging done after completing initial chemotherapy for aggressive NHL and demonstrated superior prediction of tumor response status at 2 years. These results indicate that FDG PET imaging should be combined with bone marrow biopsy for restaging aggressive NHL after completion of chemotherapy. The use of FDG PET is more accurate and should replace response assessment by CT imaging in most pateints with aggressive NHL following treatment.

Purpose To determine whether a response classification based on integration of fluorine-18–fluorodeoxyglucose positron emission tomography (FDG-PET) into the International Workshop Criteria (IWC) provides a more accurate response assessment than IWC alone in patients with non-Hodgkin's lymphoma (NHL). Patients and Methods Fifty-four patients with aggressive NHL who underwent FDG-PET and computed tomography 1 to 16 weeks after four to eight cycles of chemotherapy with cyclophosphamide, doxorubicin, vincristine, and prednisone were assessed for complete response (CR), unconfirmed CR (CRu), partial response (PR), stable disease (SD), and progressive disease (PD) by the IWC and by integrated IWC and FDG-PET (IWC+PET). Progression-free survival (PFS) was also compared between IWC- and IWC+PET-assigned response designations. Results By IWC, 17 patients had a CR, seven had a CRu, 19 had a PR, nine had SD, and two had PD. In comparison, by IWC+PET, 35 patients had a CR, 12 had a PR, six had SD, one had PD, and zero had a CRu. In separate multivariate models, PFS was significantly shorter in patients with PR than in those with a CR using IWC (hazard ratio [HR], 8.9; P = .021) or IWC+PET (HR, 29.7; P = .0003). However, when the two classifications were included in the same multivariate model, only IWC+PET was a statistically significant independent predictor for PFS (P = .008 v P = .72 for IWC). In addition, when patients with a PR by IWC and a CR by IWC+PET were compared with those with a CR by IWC and a CR by IWC+PET, there was no significant difference in PFS (HR, 1.6; P = .72), indicating that IWC+PET identified a subset of IWC-PR patients with a more favorable prognosis. Conclusion Compared with IWC, the IWC+PET-based assessment provides a more accurate response classification in patients with aggressive NHL.