Interim PET provides limited prognostic value for diffuse large B-cell lymphoma



Results from positron emission tomography after 2 and 4 weeks of standardized, dose-dense chemotherapy in patients with diffuse large B-cell lymphoma (DLBCL) failed to provide sufficient prognostic accuracy to guide therapeutic decisions, according to a report published online in the Journal of Clinical Oncology.

“Our data demonstrate that interim PET-CT fails to deliver a PPV [positive predictive value] or NPV [negative predictive value] that reflects the clinical outcome for patients with DLBCL treated with R-CHOP-14 with sufficient accuracy to guide therapeutic decisions such as treatment intensification/deintensification at the present stage,” wrote Dr. Chrisoph Mamot of the division of haematology/oncology, Cantonal Hospital of Aarau, Switzerland, and colleagues (J. Clin. Onc. 2015 July 6 [doi:10.1200/JCO.2014.58.9846]).

Although the likelihood of 2-year event-free survival (EFS) was significantly lower among patients who had positive PET results after 2 weeks of therapy (PET-2-positive), compared with PET-2-negative patients (48% vs. 74%; P = .004), a large proportion of interim PET-positive patients had favorable outcomes. This may be due to the dose-dense regimen, Dr. Mamot and colleagues said.

Patients underwent six cycles of R-CHOP (rituximab 375 mg/m2, cyclophosphamide 750 mg/m2, doxorubicin 50 mg/m2, vincristine 1.4 mg/m2, and prednisone 100 mg/m2 for 5 days) every 14 days, followed by two cycles of rituximab.

Patients who had a positive PET-2 result received another PET scan after completion of four chemotherapy cycles. The 2-year EFS for PET-4-positive and PET-4-negative patients were not significantly different.

“Our original hypothesis that an interim PET/CT at a later time point might be able to better separate patients with good or poor prognosis was not confirmed,” the authors wrote. The end-of-treatment PET provided the best prediction of good vs. poor prognosis, but this time point is too late to adapt treatment. The authors concluded that interim PET/CT in patients with DLBCL presently is not accurate enough to guide treatment decisions in individual patients.

The multicenter, prospective study evaluated 138 patients, median age 58.5 years, who had untreated DLBCL, Ann Arbor stage I (12%), II (34%), III (23%), or IV (30%).

The study was supported by grants from Amgen (Switzerland) and OncoSuisse. Dr. Christoph Mamot reported consulting or advisory roles with Roche, Novartis, Amgen, and Boehringer-Ingelheim. Several of his coauthors reported ties to industry sources.

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