Aim: To assess the prognostic value of the PET metabolic response using the Deauville Score at the end of induction (EoI) therapy. Methods: FOLL12 trial (NCT02063685) is a multicenter, phase III, randomized study with the primary objective to evaluate whether a FDG-PET (PET) and MRD (molecular residual disease) response-based maintenance therapy (experimental arm) is more effective in terms of Progression-Free Survival (PFS) than a standard maintenance therapy with Rituximab (standard arm) in patients with follicular lymphoma. Adult patients with untreated grade 1–3a FL and stage II-IV were randomized to receive standard immunochemotherapy followed by rituximab maintenance versus standard immunochemotherapy followed by a response adapted post-induction management (i.e. non-maintenance for patients in CMR and with MRD negative, short rituximab therapy for CMR (complete metabolic response) and MRD +ve cases and radioimmunotherapy followed by rituximab maintenance for non-CMR patients). EoI-PET was mandatory. All PET scans were centralized on WIDEN® platform and classified according to Deauville score (DS) in a blind independent central review. DS1-3 was considered negative (CMR), whereas DS4-5 was considered positive (not CMR). The primary endpoint was PFS. Main secondary endpoint was Overall Survival (OS) Results: Overall, 729 follicular lymphoma patients, 52% women, 89% stage III-IV disease and 40% with a high-risk FLIPI-2 score, were included in the analysis. DS at the EoI-PET resulted 1,2,3,4, and 5 in 361(49.5%), 168(23.1%), 112(15.4%), 49(6.7%) and 39(5.3%) patients, respectively. EoI-PET resulted positive in 88/729 (12%). Among the reviewers, the overall agreement (OA) on PET pos/neg result was 0.92, while agreement on positive and negative cases were 0.77 and 0.94, respectively. In the whole population of 729 patients, 5 yrs PFS (95% CI) for DS1-3 and DS4-5 was 69%(65–73) and 35%(25–46) with HR3.32(2.45–4.50), p < 0.001, respectively. The 5 yrs OS (95% CI) in DS1-3 and DS4-5 was 94%(92–96) and 81%(71–88), HR4.72(2.69–8.32), p < 0.001. The prognostic role of CMR was confirmed both in the standard and in the experimental arm of the study. In the whole population, the 5 yrs PFS (95% CI) in DS1-2, DS 3 ad DS4-5 was 74% (69–78), 55% (44–65; HR1.90 (1.36–2.66) p < 0.001) and 37%(26–48; HR 4.01 (2.90–5.54) p < 0.001); DS3 patients had an intermediate 5 yrs PFS rates between those of DS1-2 and DS4-5 patients. OS in DS3 patients had similar values to those with DS1-2. Applying a different definition of CMR (i.e., DS1-2 only) the rate of positive EoI-PET rose to 27%. Conclusion: In FOLL12 trial, EoI-PET according DS criteria was a reliable tool to stratify PFS and OS in advanced follicular lymphoma patients treated with immunochemotherapy; in addition, these data showed DS3 patients as a new category with an intermediate prognosis in terms of PFS. Keywords: Diagnostic and Prognostic Biomarkers, PET-CT No conflicts of interests pertinent to the abstract.

Introduction and Aim: Recently, in an ancillary study of FOLL12 trial (NCT02063685), total Metabolic Tumor Volume (tMTV) assessed before treatment has been demonstrated to be an independent predictor of PFS in patients receiving frontline immune chemotherapy (1). During the segmentation procedure, it has been observed that frequently spleen MTV (sMTV) heavily influenced the tMTV value, particularly in case of diffuse spleen uptake included in tMTV calculation. High tMTV could be a negative prognostic factor as it represents the tumor burden. On this basis, the aim of the current study was to evaluate the effect of the sMTV defined on baseline PET on tMTV calculation and its impact on outcome, particularly 5y-PFS (Progression Free Survival), in follicular lymphoma patients. Methods and Results: Overall, 690 patients with baseline PET were included in the analysis, 48% were older than 60 years, 89% had stage III-IV disease and 40% had a high-risk FLIPI-2 score. Overall, the 5y-PFS was 79% (95% CI, 76%–82%). Among 690 patients 469 (67.9%) did not have spleen involvement while 128 (18.5%) and 93 (13.4%) showed focal and diffuse spleen involvement, respectively. The 5y-PFS (95% CI) according the spleen status was 67% (62–72), 58% (48–67) and 61% (49–61) in patients without, with focal and with diffuse spleen involvement, respectively (p not significant). MTV calculation was performed with a threshold of 41% for segmentation. In the whole population of 690 patients, the tMTV threshold to categorized low and high tumor burden was 224 and 194 ml with and without sMTV, respectively. Assuming 200 ml as a tMTV threshold, only 16/693 pts (2.3%) changed from low to high tumor burden when the sMTV was included in the tMTV. Including sMTV in tMTV, with a threshold of 200 ml, the 5y-PFS in patients with low and high tMTV was 73% (95% CI: 67–78) and 58% (95% CI: 53–64), respectively, with a HR of 1.83 (p < 0.001). Excluding sMTV from tMTV, the 5y-PFS in patients with low and high tMTV was 72% (95% CI: 67–77) and 58% (95% CI: 52–64) with a HR of 1.80 (p < 0.001). In the two groups, HRs values for tMTV >200 ml showed negligible difference, independently from sMTV inclusion. Conclusion: These preliminary data of the FOLL12 trial showed that tMTV correlated with outcome in terms of PFS; on the contrary the metabolic spleen status defined in the baseline PET do not seem to show any prognostic added value, neither in case of focal nor in case of diffuse uptake. Finally, the inclusion/exclusion of the sMTV into the tMTV did not significantly change either the risk classification of the patients or the outcome in terms of PFS. Larger patients population are needed to confirm these data. References: R. Durmo, L. Guerra, S. Chauvie et al. “Total Metabolic Tumor Volume and tumor dissemination calculated from PET/CT scan before first line therapy are predictors of outcome in patients with follicular lymphoma” Eur J Nucl Med Mol Imaging (2022) 49 (Suppl 1): S1–S751; OP 629 Keywords: Diagnostic and Prognostic Biomarkers, PET-CT No conflicts of interests pertinent to the abstract.

Background: Classic Hodgkin lymphoma (cHL) has few pre-treatment prognostic biomarkers. Circulating tumor DNA (ctDNA) is a metrics of tumor volume and inflammation, which are both prognostic in cHL, it improves the accuracy of treatment response assessment, which is an unmet need at the interim timepoint in cHL, and it allows to accurately genotype the disease, which has technical hurdles if done of the tumor biopsy in cHL. Aims: The study aims at addressing the following questions: i) is pre-treatment ctDNA load a metrics that captures both tumor and inflammation extents in a single, measurable and radiation-free test? Can the integration of ctDNA with interim PET (iPET) improve accuracy of the sole iPET in predicting treatment outcome? Can ctDNA identify molecular groups with phenotype- and outcome-associated signatures? Methods: IOSI-EMA003 (NCT03280394) is a prospective, observational, multi-center study. The study recruited adult patients with previously untreated cHL. Blood samples were collected during staging and disease response assessment at the same time of PET scan acquisition. PET scans were centrally and blindly reviewed by a panel of nuclear medicine physicians. ctDNA was genotyped and quantified by phased variant-enhanced-LyV4.0 ctDNA CAPP-seq assay. Interim molecular response (iMR) was defined as lack tumor reporters in cfDNA collected at the interim timepoint (sensitivity 10-4). Results: A total of 215 patients were recruited. Median follow-up was 30 months. The full analysis dataset was divided into training (N=135) and validation (N=80) cohorts by using a random sample procedure. In the training cohort, ctDNA load directly associated with inflammation (B symptoms, elevated ESR), but not with disease burden: total metabolic tumor volume (TMTV), GHSG stage. The optimized threshold of pretreatment ctDNA load to stratify PFS was 850 hGE/mL of plasma (Figure 1A). In multivariable analysis, pretreatment ctDNA levels remained prognostic for PFS when controlling for either GHSG stage, TMTV, B symptoms or ESR. The validation cohort confirmed that patients with higher pretreatment ctDNA levels had inferior PFS (Figure 1B). Among intermediate and advanced stage patients, the PFS of patients with positive iPET was significantly inferior (Figure 1C). iMR was achieved in 54% patients. Patients who did not achieved iMR had a lower PFS. iMR combined with iPET had a statistically significant superior accuracy for the anticipation of progression or relapse compared to iMR or iPET alone (Figure 1D). To identify molecular subgroups within cHL, we focused on fragmentation profiles of cfDNA. cfDNA fragmentome can comprehensively represent both genomic and chromatin characteristics. Pre-treatment cfDNA fragmentation patterns were characterized by a more prominent mononucleosomal fragments abundance in 51% of patients (mono-nucleosomal cluster), whereas 33% of patients had a more prominent shift towards submono-nucleosomal fragment lengths (submono-nucleosomal cluster) (Figure 1E). Patients belonging to the submono-nucleosomal cluster had different clinical and biological nuances, including advanced stage, B-symptoms, elevated ESR, higher TMTV and total lesion glycolysis, higher mutation load, higher circulating immune suppressive cytokines and chemoattractants for monocytes and Th-cells. Accordingly, patients with submono-nucleosomal cluster had a lower PFS. Image:Summary/Conclusion: ctDNA is a validated prognostic biomarker of cHL, can improve the accuracy of interim response assessment and provide the bases for a molecular classification of cHL.