Interim PET/CT Not Useful for DLBCL

The use of interim PET/CT imaging has limited prognostic value to patients with diffuse large B-cell lymphoma (DLBCL) being treated with R-CHOP-14 (rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone given every 14 days), the results of a large trial have indicated.

No difference in overall survival at 2 years was found for patients who underwent these scans and had positive findings compared with negative findings.

“At this time, and on the basis of our study results, we conclude that interim PET/CT in patients with DLBCL is not ready for clinical use to guide treatment decisions in individual patients and it remains a research question,” wrote researchers led by Christoph Mamot, MD, of Cantonal Hospital Aarau, Aarau, in the Journal of Clinical Oncology.

Mamot and colleagues evaluated 138 patients with any stage DLBCL who were treated with 6 cycles of R-CHOP-14 followed by 2 cycles of rituximab. Patients had PET/CT scans performed at baseline, after 2 cycles of treatment, and at the end of treatment and these exams were evaluated locally and by central review.

After undergoing 2 cycles of treatment, local assessment classified 60% of the scans as positive and 40% as negative. Patients with positive scans had a significantly shorter 2-year event-free survival compared with patients with negative scans (48% vs 74%; P = .004). With central review, the 2-year event-free survival after 2 cycles was 41% for positive scans compared with 76% for negative scans (P < .001); at the end of treatment this difference was 24% compared with 72% (P < .001).

Data showed that positive PET scans after 2 cycles were associated with a difference in 2-year event-free survival after both univariable and multivariable analysis.

However, no significant difference in the 2-year overall survival between positive and negative scans was shown (88% vs 91%; P = .46).

“Our results confirmed the limited prognostic value of an interim PET/CT in DLBCL homogeneously treated with 6 cycles of R-CHOP-14 in a large prospective trial,” the researchers wrote. “Our data demonstrate that interim PET-CT fails to deliver a positive predictive value or 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/de-intensification at the present stage, even when standardized treatment and evaluation procedures for PET are being used in a reasonably large cohort of patients.”