Finding a concordant or discordant bone marrow involvement by histology or flow cytometry at dlbcl nos diagnosis implies a worse prognosis whereas pet‐fdg does not

Introduction: The prognostic value of bone marrow (BM) involvement at DLBCL diagnosis when detected by PET is controversial. The BM biopsy (BMB) analysis has outcome implication, whilst flow cytometry (FCM) has scarcely been studied in this setting. It is reported that a concordant large B cell infiltration associates a worse prognosis, whereas a discordant involvement does not alter the outcome (before WHO2016). Our aim was to analyse the prognostic value of BM involvement detected by PET, BMB or FCM in a homogeneous cohort of de novo DLBCL not otherwise specified (NOS). Methods: Retrospective two-center research of de novo DLBCL NOS cases (2013-2020 period) with a complete BM assessment – PET, BMB and FCM – at diagnosis (n = 103). BM samples were non-suitable for BMB and FCM analysis in 2 and 4 cases, respectively. Clinical and biological characteristics of the cohort were analysed and compared (descriptive statistics) according to BM infiltration by each technique. Survival outcome was evaluated by log rank test and Cox regression model, using Kaplan Meier estimator for graphical representation. Results: BM infiltration was demonstrated in 25/103 patients by PET, 15/101 by BMB and 16/99 by FCM. A 16% of cases with BM involvement by any technique presented infiltration by all of them. The PET pattern was focal in 13/25 cases (52%), diffuse in 10/25 (40%) and both in 2/25 (8%). A concordant infiltration was seen in 10/15 cases by BMB (67%) and 4/16 by FCM (25%), whereas 3/15 (20%) and 11/16 (69%) presented a discordant indolent involvement by BMB and FCM, respectively. Both concordant and discordant patterns were seen in 2/15 cases by BMB (13%) and 1/16 by FCM (6%). Figure 1 presents event-free survival (EFS) and overall survival (OS) analysis regarding each technique (median follow-up 29 months, 0.3-97). Neither focal nor diffuse PET patterns were related with outcome (1A). Both concordant and discordant infiltration by BMB were associated with a worse EFS, whereas the statistical difference was not reached for OS (1B). Both concordant and discordant infiltration were associated with a worse EFS and OS when assessed by FCM (1C). No technique maintained statistically prognostic significance in multivariate analysis. In patients with stage IV there was no difference in EFS or OS if BM was infiltrated by each technique, except for a higher OS in patients with PET+ vs PET- (HR 0.3, CI 95% 0.1-0.9). Keywords: Tumor Biology and Heterogeneity, Diagnostic and Prognostic Biomarkers, Aggressive B-cell non-Hodgkin lymphoma No conflicts of interest pertinent to the abstract.