Baseline PET-CT Does Not Predict Outcome in Localized, Low Tumor Burden Follicular Lymphoma

Abstract

In patients with high-tumor-burden follicular lymphoma (FL) treated with chemotherapy, the total metabolic tumor volume (TMTV) has been shown to predict progression-free and overall survival (PFS, OS), with an optimal cutoff value of 510 ml. We aimed to determine if baseline PET-CT parameters are associated with outcome in patients with localized, low-volume FL treated with radiation therapy (RT). The cohort comprised 36 consecutive patients with stage I-II nodal FL treated with RT from 2003-2013. The soft tissue volume (STV), maximum standardized uptake value (SUVmax), TMTV (based on the 41% SUVmax threshold), and total lesion glycolysis (TLG) were obtained from pre-treatment 18F-fluorodeoxyglucose-positron emission tomography-computed tomography (PET-CT) scans, using MIM software. Survival outcomes were calculated using Kaplan-Meier methods and compared using the log-rank test. Outcomes included PFS, with events defined as disease progression or death from any cause, and OS. The median age was 60 years (range 21-81). 190 patients (53%) had stage I FL. Ten patients (28%) had grade 3 FL and 26 patients (72%) had grade 1-2 FL. The FL International Prognostic Index (FLIPI) score was 0 in 23%, 1 in 51%, and 2 in 26%. The median SUVmax was 9.1 (range 1.3-33), TMTV was 15 ml (range 1.3-191 ml), TLG was 86 (range 1.1-2049), and STV was 43 ml (range 2.1-303 ml). No association was observed between grade 3 disease and any PET-CT parameter.The initial management strategy included radiation therapy (RT) alone in 12 patients (33%), RT and chemotherapy in 22 (61%), and RT and rituximab in 2 (6%). The median RT dose was 30.6 Gy (range 25.2-52 Gy). Chemotherapy consisted primarily of R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone; n=19; 86%). The treatment strategy employed was not associated with any PET-CT parameter.At a median follow-up of 87 months (range 17-149 months), disease progression was observed in 8 patients and death in 4. 5-year PFS and OS were 74% and 91%, respectively. No case of transformation to high-grade disease was observed.No association was found between PFS or OS and SUVmax, TMTV, TLG or STV (Table 1). No association was identified when these parameters were analyzed as continuous or dichotomized categorical variables. Likewise, no association was identified when controlling for differences in treatment approach. In this cohort of FL patients with favorable limited stage, and low to intermediate FLIPI, PET-CT parameters were not predictive of outcome. Our findings suggest that favorable features, such as low tumor burden and good risk FLIPI, are more predictive of outcome than PET/CT findings.Abstract 3011; Table 1Outcomes according to baseline PET-CT parametersPFSOSHR (95% CI)PHR (95% CI)PSUVmax0.94 (0.82-1.1)0.40.84 (0.65-1.1)0.2TMTV1.0 (0.99-1.0)0.70.99 (0.96-1.0)0.6TLG1.0 (1.0-1.0)0.71.0 (0.99-1.0)0.6STV1.0 (1.0-1.0)0.91.0 (0.98-1.0)0.5 Open table in a new tab