Complete Metabolic Response Following the First Cycle of Chemotherapy Predicts Disease-Free Interval in Patients with Non-Hodgkin's Lymphoma Evaluated by Serial PET and CT Scanning

1775 Objectives: The purpose of this prospective study was to 1) evaluate the ability of serial PET-FDG scans in predicting early response to chemotherapy and 2) to determine if chemotherapy-induced cellular responses following the first cycle will induce false positive FDG scans. Methods: Twelve patients (8 males, 4 females; mean age 63 years) with intermediate (11 pts) and low (one pt) grade NHL according to the Working Formulation Classification were enrolled. Five patients had nodal disease and 7 extranodal NHL involving the breast, pleura, bone, stomach and soft tissues. PET-FDG scans were performed at baseline and then following the first, third, sixth cycle of Rituxan + CHOP based chemotherapy and then at 12, 18, 24 months post-treatment. CT scans of the thorax, abdomen and pelvis were obtained serially at baseline after the third, sixth chemotherapy cycle, 1 and 2 years, or whenever the patient relapsed. Results: Eleven patients were evaluable and completed at least 24 months of follow-up (median = 23 month, range 13-42 months). One Stage IV patient withdrew from the study after initial workup and expired two month later. After the first cycle of chemotherapy, 9/11 pts had negative PET-FDG scans and remained free of disease for a median follow-up of 23 months. Corresponding CT scans showed persistent residual (FDG-negative) masses up to 30 months follow-up. The other two patients who had residual disease by PET-FDG after the first cycle became negative after the third; however, both recurred within 18-24 months, retreated, and remained free of disease at 34 months follow-up. Compared to CT, initial PET-FDG upstaged 5 patients (one patient from Stage III to IV, 2 patients from Stage I to II, and the remaining two from Stage II to III). Conclusions: This pilot study demonstrates the potential value of PET-FDG obtained after the first cycle chemotherapy in predicting response to therapy and interval-free disease progression and that chemotherapy led to no false positive PET-FDG findings. Research Support (if any): Grant support from Philips/ADAC.