FDG-PET in the Serial Assessment of Patients with Lymphoma in Complete Remission.

FDG-PET role in the assessment of lymphoma patients is well established but only few papers evaluated the usefulness of FDG-PET during follow up.

Aim: to prospectively investigate the value of serial FDG-PET scans in the follow up of lymphoma patients in complete remission. All lymphoma patients who achieved a complete remission were prospectively enrolled in the study and scheduled for serial FDG-PET scans at 6, 12, 18 and 24 months; further scans were then carried out on annual basis (overall 421 pts, 160 pts with Hodgkin’s Disease (HD) and 261 pts with non-Hodgkin Lymphoma (NHL) were studied). All patients had a final assessment using other imaging procedures and/or biopsy and/or clinical evolution. FDG-PET findings were reported as positive, indeterminate or negative for relapse; after comparison with all available data, PET results were categorized as true positive (TP), true negative (TN), false positive (FP), indeterminate turned out to be relapse (I+) and indeterminate turned out to be complete remission (I-).

Results: PET documented relapse in 42 cases at 6 mo (14 HD (8.8%) and 28 NHL (10.7%); in 31 cases at 12 mo (14 HD (9.5%) and 17 NHL (7.3%); in 27 cases at 18 mo (6 HD (4.5%) and 21 NHL (3.2%); in 9 cases at 24 mo (3 HD (2.4%) and 6 NHL (3.2%); and in 5 cases at > 36 mo (2 HD (2.8%) and 3 NHL (6.5%). Out of 125 scans reported as positive for relapse, 109 turned out to be TP (PPV of 87%); no false negative scan was recorded, and in the great majority of cases PET detected the presence of relapse before clinical evidence. Our results confirm that FDG-PET is a valid tool for lymphoma patients follow-up. The higher incidence of relapse occurred in both HD and NHL quite early after complete remission (at 6 and 12 months for HD and at 6, 12 and 18 months for NHD), thus confirming the usefulness of performing FDG-PET scans at these times in order to identify recurrence. The role of serial PET at later times (after 18 months for HD and 24 months for NHL) was found less relevant.