PET-CT bests contrast CT for response assessment of lymphoma

1. Contrast-enhanced CT results were weakly predictive of progression-free survival in follicular lymphoma patients after rituximab chemotherapy treatment.

2. Negative PET-CT results were strongly predictive of progression-free survival and overall survival.

Evidence Rating Level: 2 (Good)    

Study Rundown: Patients with follicular lymphoma, now more than ever, can expect extended survival time. Many of those diagnosed may die of unrelated causes while in remission. The current first-line approach to treatment of follicular lymphoma is rituximab chemotherapy. The ability to accurately assess patients’ response to rituximab and in turn use that information to make predictions about disease progression and survivability, is crucial before moving forward with further treatment. This study evaluated the role of PET-CT (with ¹⁸F-fluorodeoxyglucose as the uptake material) in rituximab response assessment. The investigators compared the results of both contrast-enhanced CT and PET-CT in patients with high-tumor burden follicular lymphoma who had received at least six cycles of rituximab chemotherapy.

After a median follow-up period of 54.8 months, they found that a promising response assessment by PET-CT strongly predicted survival and the absence of tumor progression in those patients, while a similar response assessment by contrast-enhancing CT was weakly predictive of those endpoints. The authors suggest that PET-CT, rather than contrast-enhanced CT, may be a more appropriate tool for assisting in clinical decision-making for physicians treating follicular lymphoma.

Funding: Groupe d’Etude des Lymphomes de l’Adulte (Paris, France), now LYSA (Lymphoma Study Association), Direction de la Recherche Clinique de l’Assistance Publique–Hôpitaux de Paris, Fondazione Italiana Linfomi, and the Italian Ministry of Health.

Click to read the study, published today in The Lancet

Relevant Reading: Improved survival of follicular lymphoma patients in the United States

In-Depth [retrospective cohort]: This study reviewed the PET-CT and contrasted-enhanced CT rituximab response results in patients with follicular lymphoma from three previous multicenter prospective studies (the PRIMA study, PET-Folliculaire study, and the Fondazione Italiana Linfomi FOLL05 study). 439 patients had a local PET scan assessment and 246 had centrally-reviewed scans. Patients were excluded from review if their scans were not done within 3 months of the last rituximab cycle. Since this study was retrospective, the interpretation of scan results by local physicians was not controlled. This was a major limitation of the study that was addressed by ensuring that 246 patient scans were reviewed again independently by three PET physicians using the standard five-point Deauville scale.. The primary endpoints were progression-free survival and overall survival.

In patients with a positive PET-CT, 23.2% (95% Confidence Interval [CI] 11.1-37.9) were progression free at 4 years, while 63.4% (55.9-70.0) of patients with a negative scan were progression free (p<0.0001). The 4 year overall survivability was 87.2% (95% CI 71.9-94.5) in those with a positive scan and 97.1 (93.2-98.8) in those with a negative scan (p<0.0001). Additionally, a negative PET-CT scan predicted a median progression-free survival of 74.0 months in 83% of patients. A positive scan, however, had a median progression survival of 16.9 months. Contrast-enhanced CT was weakly predictive of both endpoints (Hazard Ratio [HR] 1.7, 95% CI 1.1-2.5; p=.017).

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