FDG PET and 90Y ibritumomab tiuxetan in patients with follicular lymphoma

Despite its established utility in non-Hodgkin's lymphoma, not much is reported on FDG positron emission tomography (PET) with respect to radioimmunotherapy (RIT). In this paper we investigate its value in patients affected by follicular lymphoma (FL) before and after treatment with [90Y]Ibritumomab Tiuxetan (Zevalin(R)).

We evaluated 38 relapsed or refractory FL patients. All had a PET scan performed before and 3 months after radioimmunotherapy. Final assessment was done 9 months post-RIT, including clinical evaluation, other imaging techniques and/or biopsy, when necessary.

At the first PET scan 20 patients out of 38 had a limited disease (nodal involvement on one side of the diaphragm: 7 above and 13 below), 11 patients had nodal findings on both sides of the diaphragm and the remaining 7 patients had both nodal and extra-nodal findings. At three months post-RIT, 21 patients (55%) were in complete remission, 13 patients (34%) had a partial response (PR) and four patients (11%) had a progression disease (PD). The corresponding rates at final assessment were all consistent with the 3-month evaluation: 55% CR, 13% PR and 32% PD. FDG PET scan revealed maximal predictive values. When comparing the disease extent at relapse and the response to treatment, we could testify a higher rate of CR (75%) in patients with limited disease, while in patients with diffused nodal and/or extra-nodal findings, it was more frequent a PR or PD (66%).

Our data are concordant with the expected results on RIT, and FDG PET is confirmed to be useful in assessing treatment response. Potential correlation can also be picked out between the disease extent at relapse and the CR rate, with reasonable PET predictivity for the final outcome.