A multicenter trial has reported that PET scans in addition to the International Workshop Criteria (IWC) are more accurate than IWC criteria alone in assessing response in aggressive non-Hodgkin’s lymphoma. The details of this retrospective study appeared in the July 20, 2005, issue of the Journal of Clinical Oncology .[1]

International Workshop Criteria (IWC) are widely used and accepted for assessing the response to treatment of patients with NHL. Components of the criteria include computed tomography (CT), bone marrow biopsy (BMB) as well as clinical and laboratory information. Previous studies have shown that CT scans may have a limited ability to fully assess a patient’s response to treatment. However, PET scans have been shown to be 80 to 90 percent accurate in determining NHL responses. PET scans can distinguish between tumor and necrotic or scar tissue while CT scans cannot. This often leads to false positive results of CT scans leading to under staging of responses to induction therapy. Early results with PET encouraged researchers to evaluate the adding PET scan results to the IWC. In addition, PET scans were given general approval for reimbursement in 2001.

A previous study from Italy confirmed the value of PET scanning over conventional CT scans in the management of patients with Hodgkin’s disease (HD) and NHL after initial remission therapy.[2] In this study, researchers performed PET and CT scans after induction therapy in 41 patients with HD and 34 patients with aggressive NHL. These researchers reported that the actuarial relapse-free survival rate was 9% in the PET+ subset and 100% in the PET- subset. These authors also stated that all five patients who were PET+/ CT- had biopsies performed, which were positive in four patients. There were also two patients who were PET-/ CT+ who had only fibrosis on biopsy. These authors concluded that PET positivity after induction treatment in HD and aggressive NHL patients is highly predictive for the presence of residual disease, while PET negativity strongly suggests absence of disease.

In the current recent study, 54 patients with aggressive NHL underwent CT and PET exams one to 16 weeks after completing four to eight cycles of chemotherapy. Each patient was assessed for one of the following using the standard IWC or the IWC with PET: a complete response (CR), an unconfirmed complete response (Cru), a partial response (PR), stable disease (SD) and progressive disease (PD). Progression-free survival was also compared between IWC and IWC+PET.

Results of the study found that with IWC alone, 17 patients had a CR, seven had a Cru, 19 had a PR, nine had SD, and two had PD. By comparison, IWC+PET produced a significantly higher complete response rates: 35 patients had a CR, 12 had a PR, six had SD, one had PD, and zero had Cru. Importantly, responses by IWC and PET criteria were a much more accurate at predicting progression-free survival than IWC criteria alone. Thus, IWC plus PET better identified patients with a favorable prognosis.

Comments:  These data add further evidence to justify adding PET to CT. Since these two procedures can now be done with one machine there should be more analyses to better define the exact contribution of PET to restaging of lymphomas.

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