[Application of 18F-FDG PET for the assessment of early response to the treatment and prognosis of patients].

Positron emission tomography (PET) with [18F] fluoro-2-deoxy-D-glucose (FDG) is used for the diagnosis of various types of cancer. FDG-PET is used also for the assessment of therapeutic response as well as work-up of recurrence after therapy. Due to the characteristics of FDG-PET as an imaging tool, FDG-PET is supposed to be superior to the conventional imaging such as CT for the accurate assessment of the treatment response in patients with malignant lymphoma. Malignant lymphoma usually undergoes chemotherapy or chemoimmunotherapy as a treatment of stage III and IV patients. Recent advancement in the therapy of malignant lymphoma enables optional treatment strategies such as radioimmunotherapy with 90Y-labeled anti-CD20 monoclonal antibody or oral fludalabine for indolent non-Hodgkin's lymphoma and high-dose chemotherapy with autologous stem cell transplantation for aggressive non-Hodgkin's lymphoma. The purpose of the present study was to determine the clinical value of FDG-PET for the early assessment of therapeutic response of malignant lymphoma. Twenty-six patients with malignant lymphoma were enrolled in the study. The subject consists of 10 patients with follicular lymphoma, 9 diffuse large B-cell lymphoma, and others. Therapeutic regimens were rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) for 19 patients, CHOP and ABVD (doxorubicin, bleomycin, vinblastine, dacarbazine) for 2 patients each, and others. FDG-PET was performed before the initiation of therapy in all patients and after the therapy of 1-2 courses in 5 patients; and 3-4 courses, 5-6 courses, and 7-8 courses in 7 patients each. Complete remission on the PET (CR(PET)) was defined as the FDG uptake lower than the background and compared with the final response assessment. CR(PET) was acquired in 4 of 5 patients at 1-2 courses, 6 of 7 at 3-4 courses, 4 of 7 at 5-6 courses, and 3 of 7 at 7-8 courses. In the group of 7-8 courses, final response assessment revealed 2 patients excess of CR. In patients who underwent multiple PET studies during the treatment, all 4 patients showed CR(PET) in its first assessment, and maintained CR thereafter. The present study revealed that most of the patients achieved CR(PET) up to 4 courses of therapy. The cases with remaining FDG uptake at this time were likely to be resistant to the therapy. The early assessment of therapeutic response may be accurately assessed by FDG-PET as early as 2 or 4 courses of therapy. Residual uptake of FDG in the lesion would be considered to be subject to the new therapeutic strategy. Clinical usefulness of the strategy based on the early response assessment with FDG-PET would be confirmed by the clinical trials.