Positron emission tomography (PET) for diagnosis and therapy management of malignant lymphomas

The management of patients who have malignant lymphomas requires functional methods to differentiate residual soft tissue masses. Positron emission tomography (PET) was performed in patients with histologically proven malignant lymphomas prior to the onset of second-line chemotherapy to examine tumor viability. Twenty patients (68 malignant lesions and 3 benign lesions) with Hodgkin lymphomas (HL) as well as 26 patients (46 malignant lesions and 1 benign lesion) with non-Hodgkin lymphomas (NHL) were studied with fluorine-18-deoxyglucose (FDG). Oxygen-15-labelled water was used in addition in 14 patients with 25 lesions to obtain information on the tissue perfusion. PET with FDG is highly sensitive for the detection of viable tumor tissue, all malignant lesions being correctly classified in this study. We noted no statistically significant difference in FDG metabolism for Hodgkin and non-Hodgkin lymphomas. Even lymph-node metastases (<1 cm) were detected with PET and FDG. The possible limitations are inflammatory processes, which may obscure tumor detection because of the increased FDG uptake, as well as malignant lesions with low FDG uptake as a result of reduced perfusion. Comparison of tumor perfusion and FDG uptake showed a significant nonlinear correlation of r-=0.78 between the two parameters. Two patients with scar tissue and no evidence of malignancy were excluded from blood stem-cell support therapy as a result: of the PET study. The data demonstrate that PET is a useful tool for making a diagnosis and deciding on therapy for malignant lymphomas.