Abstract: Introduction: The role of minimal residual disease (MRD) in Multiple Myeloma (MM) as a surrogate biomarker of patients' outcome, as well as the prognostic information of functional imaging response after treatment have been established in recent years. Furthermore, the predictive relevance of sustained MRD negativity assessed by marrow and imaging techniques and its association with an excellent outcome is emerging in clinical trials. Diffusion-weighted whole-body MRI (DW-MRI) is increasingly used in the management of MM patients, but data regarding the predictive role of sustained DW-MRI response after treatment are lacking. The Myeloma Response Assessment and Diagnosis System (MY-RADS) recommendations have established criteria for Response Assessment Category (RAC) (Messiou C et al, Radiology 2019) with a 5 point scale defining the probability of complete imaging response (i.e. RAC 1) or progressive disease after treatment (i.e. RAC 5). We implemented the RAC criteria in our clinical practice and DW-MRI at 1-year in MM patients treated with autologous stem cell transplantation (ASCT) followed by maintenance therapy. Patients and methods: We retrospectively analyzed the outcome of 57 newly diagnosed MM patients (median age 61 years) diagnosed at our institution from January 2015 to December 2019 receiving maintenance therapy after ASCT. Patients underwent DW-MRI evaluation according to MY-RADS criteria at day +100 after ASCT, before maintenance, and after 1 year with the aim of monitoring imaging residual disease. Bone marrow samples were collected for MRD assessment by 8-color FCM (sensitivity 10-5) at day +100 after ASCT, before maintenance, and after 1 year. We focused on sustained 1-year DW-MRI negativity evaluated according to RAC response, and its potential predictive role at that timepoint on progression free survival (PFS) and overall survival (OS). In patients with available 1-year MRD evaluations, concordance between 1-year MRD and DW-MRI results was calculated and the level of agreement was expressed by Cohen's kappa statistics. Results: Out of 57 patients, 23 (40%) were ISS stage 3 and 14 (25%) showed high risk cytogenetics. Patients were treated with the following induction regimens: VTD 42, VRD 5, Dara-VRD 6, KRD 3, KCD 1. Single ASCT with MEL200 conditioning was performed in 33 patients (58%), whereas 24 patients (42%) received double ASCT. Subsequent maintenance was performed with lenalidomide (49 patients, 86%) or daratumumab-lenalidomide (8 patients, 14%). Response rates after ASCT were PR 9%, VGPR 23%, CR 51% and sCR 17%. According to MY-RADS, a complete imaging response (RAC1) at day +100 after ASCT was observed in 34 patients (60%). Sustained 1 year complete imaging response during maintenance therapy was observed in 43 patients (75%). Some residual disease was identified at that timepoint in 14 patients (25%) [RAC 2: 6 (11%), RAC & gt; 2: 8 (14%)]. After a median follow up of 36 months, PFS and OS were significantly longer in patients with sustained 1-year imaging negativity, compared to patients with imaging residual disease (RAC 1 vs RAC ≥2): median PFS 56 vs 24,1 months, p & lt;0,0001, HR 0,11 (95% CI: 0,030-0,382); median OS NR vs 40,5 months, p & lt; 0,0001, HR 0,05 (95% CI: 0,006-0,364). MRD at 1-year timepoint was available in 30 patients and was negative in 28 (93%) cases. Concordance between 1-year DW-MRI and MRD results was high (97%, kappa 0,783: 7% both positive, 90% both negative). Conclusion: Our real-life data analysis confirms the predictive value of imaging residual disease assessment with DW-MRI after ASCT and highlights the importance of achieving sustained imaging MRD negativity during maintenance therapy regardless of different treatment strategies. Moreover, given the high rates of CR seen in patients with MM with novel effective treatment combinations, the detection of residual disease with the combined evaluation of marrow and functional imaging techniques during maintenance therapy can help the physician to identify patients with increased risk of early relapse and particularly poor prognosis. Our preliminary data regarding the high concordance observed between DW-MRI and MRD results during maintenance therapy suggest that DW-MRI could represent a reliable non-invasive technique to monitor residual disease. Disclosures Belotti: Janssen: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy; GSK: Membership on an entity's Board of Directors or advisory committees. Ribolla: Janssen: Membership on an entity's Board of Directors or advisory committees. Cancelli: Amgen: Membership on an entity's Board of Directors or advisory committees. Roccaro: Amgen, Celgene, Janssen, Takeda: Membership on an entity's Board of Directors or advisory committees; AstraZeneca,: Research Funding; Associazione Italiana per la Ricerca sul Cancro (AIRC): Research Funding; European Hematology Association: Research Funding; Fondazione Regionale per la Ricerca Biomedica (FRRB), Transcan-2 ERA-NET: Research Funding. Rossi: Sanofi: Honoraria; Jazz: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Consultancy, Honoraria; Astellas: Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Alexion: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees. Tucci: janssen: Membership on an entity's Board of Directors or advisory committees; Gentili: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees.

Abstract: Introduction: The role of functional imaging in Multiple Myeloma (MM) has evolved in recent years due to the increasing availability of high platform imaging and the prognostic information of imaging response after treatment, as observed in PET/CT studies. Diffusion weighted whole body MRI (DW-MRI) is a functional imaging technique with an emerging role in the management of MM patients (pts) due to its high sensitivity, but consistent data regarding its prognostic role in the detection of residual disease after treatment in MM are lacking. The Myeloma Response Assessment and Diagnosis System (MY-RADS) imaging recommendations have been recently published (Messiou C et al, Radiology 2019) in order to promote standardization in response assessment. Criteria for Response Assessment Category (RAC) have been proposed with a 5 point scale defining the probability of complete imaging response (i.e. RAC 1) or progressive disease after treatment (i.e. RAC 5), but this score still needs to be validated in clinical practice. For this purpose, we performed an external validation of RAC criteria according to MY-RADS in newly diagnosed MM pts in order to evaluate the prognostic role of this technique after autologous stem cell transplantation (ASCT). Furthermore, we tried to correlate the results of MY-RADS with those of minimal residual disease (MRD) assessment by flow cytometry (FCM). Patients and methods: We retrospectively analyzed the outcome of 60 MM pts (median age 63 years) diagnosed between January 2016 to January 2020 who underwent DW-MRI evaluation to assess the response at day +100 after ASCT, before maintenance. After anonymization, images were reviewed according to MY-RADS by Radiologists who were blinded to the results of clinical and biological data. Post ASCT Progression free survival (PFS) was calculated from the date of last ASCT (the second one in case of double ASCT) until progression or death from any cause. The predictive role of MRI RAC response on outcome was analyzed. Bone marrow samples were collected before maintenance for MRD by 8-color FCM (sensitivity 10-5). In pts with MRD evaluations, exploratory PFS analysis was performed; concordance between MRD and DW-MRI results was calculated and the level of agreement was expressed by Cohen's kappa statistics. Results: out of 60 pts, 21 (35%) were ISS stage 3 and 13 (22%) showed high risk cytogenetics. Pts were treated with the following induction regimens: VTD 51, VRD 4, Dara-VRD 3, VCD 1, KRD 1. Single ASCT with MEL200 conditioning was performed in 41 pts (68%), %), whereas 19 patients (32%) received double ASCT. Response rates were VGPR 18,3%, CR 51,6% and sCR 13,3%. MRD before maintenance was available for 44 pts and was positive in 20 (45,5%). According to MY-RADS, a complete imaging response after transplant was observed in 36 (RAC 1: 60%). Some residual MM was identified in 24 (40%) [RAC2: 20 (33%), RAC3: 3 (5%), RAC4: 1 (2%), respectively]. After a median of 28 months, post ASCT PFS was significantly longer in pts with RAC 1 vs RAC ≥2: median NR vs 26,5 months, p 0,017, HR 0,29 (95% CI: 0,10-0,80). Concordance between WB-MRI and MRD results was low (52%, kappa 0,017: 16% both positive, 36% both negative). PFS according to DW-MRI response and MRD was significantly better for pts DW-MRI RAC1 and MRD negative before maintenance, compared to pts with RAC ≥2 and MRD positive results (PFS NR vs 10,6monts; p 0.012, HR 0,11 - 95%CI: 0,02-0,62). Intermediate PFS was observed for pts with either imaging or MRD positive results (PFS NR), with a significantly different outcome of the three subgroups (p 0,021) Figure 1. In 30 pts achieving CR or sCR, residual disease was identified in 14 (47%); in 4 of them by FCM only, in 8 by DW-MRI only, including two pts in sCR, and in two by both techniques. Conclusion: given the high rates of CR seen in pts with MM with new treatment approaches, DW-MRI is a powerful tool to better evaluate the prognosis of pts treated with novel combinations and ASCT. Our external validation of RAC criteria highlights the ability of DW-MRI to stratify pts with different outcome and promotes the standardization in reporting functional imaging response after treatment. The low concordance between DW-MRI response and MRD results suggests that these two techniques may be complementary for the definition of response: their combined use could help clinicians to better refine the prognosis of MM pts achieving CR Figure 1 Disclosures Belotti: Amgen: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Jannsen: Membership on an entity's Board of Directors or advisory committees. Rossi:Jazz: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria; Novartis: Other: Advisory board; Astellas: Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Consultancy, Honoraria; Pfizer: Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria; Celgene: Membership on an entity's Board of Directors or advisory committees; Alexion: Membership on an entity's Board of Directors or advisory committees.

Abstract: Hematologic patients affected by coronavirus disease 2019 (COVID‐19) have a severe prognosis and a 30‐day mortality rate of 39.2%. The need for oxygen and ongoing hematologic treatment at the presentation of COVID‐19 are the main risk factors associated with a worse outcome.

Abstract: Abstract 4711 Background: Myeloproliferative diseases (MPDs) are a group of hematological malignancies characterized by the abnormal increase of different blood cells in peripheral blood and in other hematological organs. The molecular pathways involved in disease pathogenesis and progression as well as in drug sensitivity and resistance are not fully elucidated yet. Given the physiological similarity to mammals, the zebrafish (ZF) could accelerate the study of the molecular basis of these diseases. In the last decade several human leukaemia associated oncogenes have been transiently over-expressed in ZF embryos in order to perturb the myelo-erythroid compartment, with the aim to create experimental models to discover new molecular pathways that can became potential targets for new chemical compounds. Methodogy: We took advantage of the binary Gal4/UAS system to express oncogenic human HRAS in the ZF hematopoietic compartment. We used the tg(MAZe) driver line, a specific transgenic line that allows random mosaic expression of Gal4-VP16 after heat shock(hs) treatment(1). This driver line was mated with a tg(UAS:eGFP-HRASV12)(2) responder line in order to mimic somatic events leading to human oncogene expression. Results: Surprisingly a single heat shock at 30hpf, (referred here as HRASV12hs) induces human HRASV12 expression in hematopoietic progenitors as judged by the expansion of the hematopoietic tissue. Histological analysis showed an increased number of monocytes/macrophages. Blood smear of HRASV12hs larvae showed the expansion of blasts and myeloid precursors. Quantitative analysis of gene expression highlights a remarkable increase of myelo-erythroid restricted genes associated with a slight increase of staminality markers (pu1, mpx, lmo2, mpl, CD41 and c-myb). Moreover fish raised to adulthood developed hyper-plastic kidney marrow, the site of definitive haematopoiesis, the equivalent of mammalian bone marrow. Conclusions and Future Perspectives: The combination of hyper-proliferation of blood cells associated with the expansion of the hematopoietic compartment that we found in this model reproduces the pathological features of human myeloproliferative disorders. This study shows that it is possible to drive the expression of leukemia associated oncogenes to the hematopoietic compartment in developing ZF thus reproducing some of the features of human blood malignancies in an in vivo model. Our Group is now testing different driver lines in order to induce oncogene expression in earliest hematopoietic progenitors and is focusing on different responder lines expressing human oncogenes involved in hematopoietic malignancies. Disclosures: No relevant conflicts of interest to declare.

Abstract: Diffusion‐weighted whole‐body MRI (DW‐MRI) is increasingly used in the management of multiple myeloma (MM) patients, but data regarding the prognostic role of DW‐MRI imaging response after treatment are lacking. The Myeloma Response Assessment and Diagnosis System (MY‐RADS) imaging recommendations recently proposed the criteria for response assessment category (RAC) with a 5‐point scale in order to standardize response assessment after therapy, but this score still needs to be validated. Methods We investigated the prognostic role of RAC criteria in 64 newly diagnosed MM patients after autologous stem cell transplantation (ASCT), and we combined the results of MY‐RADS with those of minimal residual disease (MRD) assessment by multiparametric flow cytometry (MFC). Results Superior post‐ASCT PFS and OS were observed in patients with complete imaging response (RAC1), with respect to patients with imaging residual disease (RAC≥2): median PFS not reached (NR) versus 26.5 months, p  = 0.0047, HR 0.28 (95% CI: 0.12–0.68); 3‐year post‐ASCT OS 92% versus 69% for RAC1 versus RAC ≥2, respectively, p  = 0.047, HR 0.24 (95% CI: 0.06–0.99). Combining MRD and imaging improved prediction of outcome, with double‐negative and double‐positive features defining groups with excellent and dismal PFS, respectively (PFS NR vs. 10.6 months); p  = 0.001, HR 0.07 (95%CI: 0.01–0.36). Conclusion The present study supports the applicability of MY‐RADS recommendations after ASCT; RAC criteria were able to independently stratify patients and to better predict their prognosis and the combined use of DW‐MRI with MFC allowed a more precise evaluation of MRD.