Role of FDG-PET As Prognostic Indicator in Patients with Follicular Lymphoma(FL) After Immunochemotherapy Induction. A Retrospective Study From the Fondazione Italiana Linfomi

Quality of response assessed with [¹⁸F]fluorodeoxyglucose - Positron Emission Tomography (FDG-PET) is confirmed as a strong independent prognostic factor in patients with Hodgkin lymphoma and Diffuse Large B-Cell Lymphoma. Recently the prognostic role of response assessment with PET was also shown in patients with Follicular Lymphoma (FL) (Trotman et al JCO 2011). We conducted a retrospective analysis to investigate the role of FDG-PET after immunochemotherapy in FL.

The study was designed as a retrospective unplanned analysis of newly diagnosed FL patients randomized among R-CVP, R-CHOP, R-FM in the FOLL05 clinical trial (NCT00774826). To be included in the study patients should have confirmed eligibility for the FOLL05 trial, have available data on clinical presentation, treatment details and results, and on follow-up. As mandatory patients should have undergone staging and restaging at the end of treatment with FDG-PET. Local PET interpretation was used to identify clearly positive and clearly negative cases. For this phase of the study uncertain cases were not analyzed for study endpoints: centralized review is ongoing. Contrast enhanced computed tomography (CECT) scans were also collected to confirm quality of response: in particular a cut off of 1.5 cm for the maximum transverse diameter of residual lymph nodes was considered to separate Complete vs. Partial remissions according to International Workshop Criteria (IWC) (Cheson et al JCO 1999). The primary study endpoint was Progression Free Survival.

Among 534 patients enrolled in the FOLL05 trial, 114 cases fulfilled eligibility criteria for this study. Baseline patients characteristics did not differ from the overall FOLL05 patient population. In particular FLIPI was 0–1 in 23%, 2 in 42% and 3–5 in 35%. First-line immunochemotherapy, included R-CHOP (36 pts.), R-CVP (33), and R-FM (45). No maintenance therapy with Rituximab was given. Overall response rate at the end of therapy, defined according to IWC, was 97% including a 78% complete remissions (CR) rate. Baseline PET scan was positive in all patients. In 16 cases an interim PET was also available and resulted clearly positive in 6 patients (38%). At the end of treatment 10 cases had inconclusive final PET results and were excluded from subsequent analyses; a clearly positive PET scan was recorded in 26 out of the remaining 104 (25%). In univariate logistic analysis number of nodal sites (>4) was predictive of final positive PET. Although a trend towards a higher rate of PET positive scans was observed with increasing FLIPI and FLIPI2 this difference was not statistically significant. The rate of patients with negative final PET was 81%, 57%, and 60% for those in CR, PR, and less than PR (Fisher exact test: P=0.021). Assessing response with International Harmonization Project (IHP) criteria (Cheson et al JCO 2007), that also consider PET, 14/74 (19%) of patients previously defined in CR according to IWC were changed to PR and 13/23 (57%) of those in PR were switched to CR. The CR rate changed from 78% to 75% with an agreement rate of 70% between IWC and IHP. With a median follow up of 28 months (range 9–56), 3 year PFS was 68% (95% IC 54%–79%). In univariate analysis a shorter 3yr PFS was observed in post-treatment PET+ vs. PET- patients: 48% vs 84% (log rank p=0.036, HR 2.34, 95% CI 1.03–5.3). A positive final PET was confirmed as a poor prognostic factor when adjusted by FLIPI and FLIPI2 (HR 2.33 P=0.048, and HR 2.41 P=0.039, respectively). Prognostic role of final PET was not affected by treatment arm or by any of analyzed prognostic factors. Finally a trend toward a prolonged duration of remission was observed for patients who achieved a PET negative CR, compared with PET+ CRs and and both PET+/− PRs.

This FOLL05 ancillary study confirms that post-treatment PET-CT can modify response allocation and is a predictor of PFS after first line immunochemotherapy in patients with FL. If the prognostic role of PET assessment of response will be confirmed in a larger series and in prospective studies a response adapted treatment strategy could be tested also in FL.

Di Raimondo:Celgene: Honoraria, Speakers Bureau; Janssen: Honoraria, Speakers Bureau.