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Background: Novel agents capable of inducing deeper responses dramatically improve the prognosis of patients with multiple myeloma (MM). Innovative technologies such as multiparameter flow cytometry (MFC) and next-generation sequencing (NGS) are utilized to assess minimal residual disease (MRD) for further stratification of patients who achieve a complete response (CR). EuroFlow-next-generation flow (EuroFlow-NGF) is one of the gold standard MFC methods. Recently, both NGF and NGS have been used in many clinical trials to assess MRD levels associated with progression-free survival (PFS) and overall survival (OS). The present study prospectively assessed MRD levels by both NGF and NGS to elucidate the prognostic impact of both methods and clarify their characteristics in MM patients in an autologous stem cell transplantation (ASCT) setting. Methods: We prospectively assessed the response in Japanese patients with newly diagnosed MM who underwent ASCT and lenalidomide-based maintenance therapy at multiple Japanese medical centers between September 2016 and July 2021. The diagnosis of MM and patients' responses to therapy were assessed using the IMWG criteria. Only patients with CR or stringent CR on days 100-365 post-ASCT were included, and bone marrow (BM) samples were obtained to assess MRD. Four milliliters of BM was divided equally. Cells derived from 2 mL BM were analyzed by the NGF method (Flores-Montero et al., Leukemia 2017) at Kanazawa University, and DNA extracted from the remaining 2 mL BM cells was processed by Adaptive Biotechnologies' standardized NGS-MRD assay (Seattle, WA) (Ching et al., BMC Cancer 2020) to assess MRD levels. MRD levels in BM were also monitored at 1-year (± 20 days) and 2-year (± 20 days) post-ASCT. The prognostic value of MRD levels in BM was assessed, and their correlation between NGF and NGS was compared at a cut-off value of 1×10 -5. Sustained MRD negativity was defined as the maintenance of MRD negativity in the BM for more than 6 months. BM cells were analyzed for high-risk cytogenetics (del(17p), t(4;14), and t(14;16)) by FISH. Results: A total of 60 patients (male = 29, female = 31) underwent bortezomib-based induction therapy, ASCT conditioned with high-dose melphalan, and lenalidomide-based maintenance. The median age was 62 years at the ASCT (range 36-71; ISS 1 [n = 13], 2 [n = 24], and 3 [n = 23]). Thirty-three percent of patients showed high-risk chromosomal abnormalities (del17p (n=11), t(4;14) (n=10), t(14;16) (n=2)), 3 patients had double hit diseases, and five patients had extramedullary diseases. With a median follow-up of 3 years, the 3-year progression-free survival (PFS) and 3-year overall survival (OS) rates were 69.2% and 94.2%, respectively. In total, 148 samples were analyzed using NGF and 138 were analyzed using NGS. The rates of MRD negativity at least once using NGF and NGS were 80% and 61%, respectively. The patients who achieved at least one MRD negativity exhibited significantly better 3-year PFS (82.9% by NGF; 84.8% by NGS) than those who did not (P < 0.0001, 0% by NGF; P = 0.005, 49.1% by NGS). Patients who sustained MRD negativity for more than 6 months also showed significantly better 3-year PFS (96.7% by NGF; 92.3% by NGS) compared with those without sustained MRD negativity (Figure; P < 0.0001, 37.1% by NGF; P < 0.01, 50.9% by NGS). The MRD levels between the NGF and NGS methods were significantly correlated with each other (r = 0.9295, P < 0.0001). Among the 17 patients who developed PD after ASCT, seven cases showed discrepancies in the MRD results and two cases in which one case was MRD-positive and the other was MRD-negative by both methods progressed with extramedullary diseases. Five of the seven cases were MRD-positive by NGS and MRD-negative by NGF. Conclusions: In this prospective comparison study of MRD assessment in BM cells using EuroFlow-NGF and NGS approaches, MRD levels highly correlated with each other, and MRD negativity and sustained MRD negativity were significantly associated with prolonged PFS. Multiple MRD assessments by NGF or NGS are essential for predicting durable remission and prolonged clinical outcomes. Figure 1 Figure 1. Disclosures Takamatsu: Bristol-Myers Squibb: Honoraria, Research Funding; Adaptive Biotechnologies, Eisai: Honoraria; SRL: Consultancy; Janssen: Consultancy, Honoraria, Research Funding. Yoshihara: Bristol-Myers Squibb: Honoraria; Janssen: Honoraria; Novartis: Honoraria. Matsumoto: Sanofi: Honoraria; Janssen: Honoraria; Ono: Honoraria; Bristol-Myers Squibb: Honoraria. Yamashita: Janssen: Honoraria; Bristol-Myers Squibb: Honoraria; celgene: Honoraria; Takeda: Honoraria. Fuchida: Takeda Pharmaceutical Co., Ltd.: Honoraria; Ono Pharmaceutical Co., Ltd.: Honoraria; Janssen Pharmaceutical K.K.: Honoraria; Sanofi: Honoraria; Bristol-Myers Squibb Co., Ltd.: Honoraria; Celgene Co., Ltd.: Honoraria. Hiragori: BML: Current Employment. Suzuki: Amgen: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria; ONO: Honoraria; Novartis: Honoraria; Sanofi: Honoraria; Abie: Honoraria; Janssen: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Honoraria, Research Funding. Nakao: Symbio: Consultancy; Kyowa Kirin: Honoraria; Novartis Pharma: Honoraria; Alexion Pharma: Research Funding. Durie: Amgen: Other: fees from non-CME/CE services ; Amgen, Celgene/Bristol-Myers Squibb, Janssen, and Takeda: Consultancy.

Background: Autologous stem cell transplantation (ASCT) in conjunction with therapeutic drugs such as bortezomib, thalidomide, and lenalidomide can dramatically improve response rates and the prognosis of patients with multiple myeloma (MM). However, most patients with MM are considered to be incurable, and relapse owing to minimal residual disease (MRD) is the main cause of death among these patients. Here we utilized a next-generation sequencing (NGS) approach for MRD assessment, which offers at least 1 to 2 logs greater sensitivity (10-6) compared to allele-specific oligonucleotide PCR (ASO-PCR) and flow cytometry, respectively (Faham et al Blood 2012). Previous studies have shown that NGS-based MRD assessment 90 days post-ASCT has prognostic value (Martinez-Lopez et al Blood 2014). In this study, we compared the prognostic value of MRD assessment in autografts and bone marrow (BM) samples from MM patients in the ASCT setting. Methods: One hundred and twenty-three Japanese patients with newly diagnosed MM who received various induction regimens prior to ASCT were retrospectively analyzed. All patients received ASCT and were followed between June 15, 2004 and April 25, 2015. All patients had achieved a partial response (PR) or better after ASCT. Analyzed samples included: (1) BM slides from 96 MM patients at diagnosis, (2) fresh/frozen BM cells from 27 MM patients at diagnosis, (3) autografts and/or (4) post-ASCT BM cells obtained at the time of best response based on serum and urine tests. IGH-based ASO-PCR was performed as described previously (Methods Mol Biol 2009). NGS-based MRD assessment was performed using the immunosequencing platform (Adaptive Biotechnologies, South San Francisco, CA) (Martinez-Lopez et al Blood 2014). Results: We compared MRD results in 51 samples assessed by ASO-PCR and NGS. We observed a high correlation between NGS and ASO-PCR results at MRD levels of 10-5 or higher (r=0.86, P Conclusions: In this study, we show the prognostic value of NGS-based MRD assessment in autografts of patients with MM. The NGS platform has improved sensitivity compared with ASO-qPCR in detecting MRD in autografts. Importantly, this retrospective study suggests that therapeutic intervention based on NGS-based MRD positivity has a significant effect on patient outcome in the post-ASCT setting. Disclosures Zheng: Adaptive Biotechnologies Corp.: Employment, Equity Ownership. Moorhead:Adaptive Biotechnologies Corp.: Employment, Equity Ownership. Faham:Adaptive Biotechnologies Corp.: Employment, Other: Stockholder.

Background: Most patients with multiple myeloma (MM) are considered to be incurable, and relapse, due to minimal residual disease (MRD), is the main cause of death among these patients. Even though allele-specific oligonucleotide real-time quantitative PCR (ASO-qPCR) of immunoglobulin heavy chain gene rearrangement has been used to assess the MRD in MM due to its excellent sensitivity and specificity, ASO-qPCR has a major limitation in its relative quantification method because it needs a reference standard curve, which is usually made with dilutions of diagnostic myeloma DNA or from plasmids containing the target IgH rearrangement gene. Recently, droplet digital PCR (ddPCR) was developed to perform reliable absolute quantification of target genes. Based on the principle of single target gene detection, the sensitivity can be increased when the larger amount of DNA is analyzed. Here we assessed the prognostic value of MRD assessment in autografts from MM patients in the autologous stem cell transplantation (ASCT) setting using ASO-qPCR, ddPCR and next-generation sequencing (NGS) approaches. Methods: Twenty-three Japanese patients with newly diagnosed MM who received various induction regimens prior to ASCT without any post-ASCT therapy were retrospectively analyzed. Median age 57 (range 39-67); males 11, females 12; ISS 1 (n=7), 2 (n=12), 3 (n=3), not assessed (n=1). 11 patients were analyzed by G-banding and FISH (t(4;14), del17p, t(14;16)) and 4 patients showed high-risk chromosomal abnormalities (t(4;14) (n=2), t(14;16) (n=1), -13 by G-banding (n=1)). All patients had achieved a very good partial response (VGPR) or better after ASCT. Analyzed samples included: (1) BM slides from 20 MM patients at diagnosis, (2) fresh/frozen BM cells from 3 MM patients at diagnosis, and (3) obtained autografts. IGH-based ASO-qPCR was performed as described previously (Methods Mol Biol 2009). ddPCR was performed by the QX200 Droplet Digital PCR system (Bio-RAD Inc.) with a total 6000 ng of genomic DNA combined with the same ASO-primers and TaqMan-probes used in the ASO-qPCR. Droplets were generated by the QX200 droplet generator. End-point PCR (40 cycles) was performed on a C1000 Touch Thermal cycler (Bio-RAD Inc). The PCR product was loaded in the QX200 droplet reader and analyzed by QuantaSoft 1.7.4 (Bio-Rad Inc). NGS-based MRD assessment was performed using the immunosequencing platform (Adaptive Biotechnologies, South San Francisco, CA) (Martinez-Lopez et al Blood 2014). Results: Nineteen patients could be analyzed by ASO-qPCR and ddPCR, while all 23 patients could be analyzed by NGS. We compared MRD results in autografts between ddPCR and NGS. We observed a high correlation between ddPCR and NGS results of MRD (r=0.82, P Conclusions: In this study, we showed the prognostic value of ddPCR and NGS-based MRD assessment in autografts of patients with MM. Although the ddPCR had improved sensitivity in detecting MRD in autografts and demonstrated higher prognostic value compared with ASO-qPCR, the NGS platform showed the highest sensitivity and prognostic value among these methods. Disclosures Zheng: Adaptive Biotechnologies Corp: Employment, Equity Ownership. Moorhead:Adaptive Biotechnologies Corp: Employment, Equity Ownership. Faham:Adaptive Biotechnologies Corp.: Employment, Other: Stockholder.

Background: Although molecular complete remission (mCR) in multiple myeloma (MM) can be assessed by allele-specific oligonucleotide (ASO)-PCR, this technique requires preparation of clonotype-specific primers for each individual, which is laborious and time-consuming. We utilized the LymphoSIGHTTM platform, which employs consensus primers and next-generation sequencing (NGS) to amplify and sequence all rearranged immunoglobulin gene segments present in a myeloma clone, to assess mCR. This technique has been shown to have 1-2 logs greater sensitivity compared to ASO-PCR and flow cytometry, respectively (Faham et al, Blood 2012). Usage of the sequencing method for minimal residual disease (MRD) detection in MM may provide increased sensitivity and specificity, while overcoming the challenges associated with ASO-PCR. We compared the LymphoSIGHTTM method with ASO-qPCR for MRD detection in autografts and bone marrow (BM) in the autologous peripheral blood stem cell (PBSC) transplantation (ASCT) setting. Methods: One hundred and nine Japanese patients with newly diagnosed MM who received various induction regimens prior to ASCT were retrospectively analyzed. All patients had achieved a partial response (PR) or better after ASCT. BM slides from 84 MM patients and fresh/frozen BM cells from 25 MM patients at diagnosis, as well as autografts/post-ASCT BM cells from each patient, were obtained for DNA extraction. IGH-based ASO-qPCR was performed as described previously (Methods Mol Biol 2009). Using universal primer sets, we amplified IGH variable (V), diversity (D), and joining (J) gene segments, IGH-DJ, and IGK from genomic DNA. Amplified products were subjected to deep sequencing using NGS. Reads were analyzed using standardized algorithms for clonotype determination. Myeloma-specific clonotypes were identified for each patient based on their high frequency in BM samples. Results : Myeloma clonotypes could be identified in autografts/post-ASCT BM cells in 98 of 109 patients (90%) and by ASO-qPCR in 63 of 101 patients (62%). MRD by NGS was assessed in autografts of 89 patients. 70 of 89 patients (79%) were positive by NGS; 28 of 62 patients (45%) were positive by ASO-qPCR. Although we observed a high correlation between NGS and PCR MRD results at MRD levels of 10-5 or higher, the sensitivity of ASO-PCR was 10-4-10-5, whereas that of NGS was 10-6 or lower when a sufficient amount of DNA was available for analysis. Eight cases where MRD was not detected in the autograft by NGS (MRDNGS(-)) and 38 MRDNGS(+) cases received post-ASCT therapy using novel agents such as bortezomib/lenalidomide/thalidomide, while 11 MRDNGS(-) cases and 32 MRDNGS(+) cases were followed without post-ASCT therapy. The MRDNGS(-) cases without post-ASCT therapy showed significantly better progression-free survival (PFS) than the MRDNGS(+) cases without post-ASCT therapy (P = 0.012) (Figure 1A) although overall survival rates were comparable between these groups. To investigate the value of sensitive detection by NGS, we compared PFS in 11 MRDNGS(-) cases (Group 1) with the 12 MRDNGS(+) cases where MRD was not detected by ASO-qPCR (MRDASO(-)) (Group 2). The patients in both groups did not receive any post-ASCT therapy. Group 1 showed significantly better PFS than Group 2 (P = 0.027) (Figure 1B). Furthermore, 9 MRDNGS(-) in post-ASCT BM cases tended to show a better PFS than 18 MRDNGS(+) in post-ASCT BM cases (P = 0.075) (Figure 1C). In a multivariate analysis, post-ASCT therapy using novel agents (P Conclusions: In this study, we showed the prognostic value of MRD detection using the NGS-based LymphoSIGHT platform in autografts of patients with MM who received and in those who did not receive post-ASCT therapy with novel agents. The NGS platform has improved sensitivity compared with ASO-qPCR in detecting MRD in autografts. Patients with low level MRD detected by NGS but not by ASO-qPCR have worse prognosis compared to patients who are MRD negative by sequencing, which underscores the need for sensitive detection. Figure 1 Figure 1. Disclosures Zheng: Sequenta, Inc.: Employment. Moorhead:Sequenta, Inc.: Employment. Faham:Sequenta, Inc.: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees.

[Background] Body cavity-based lymphoma (BCBL) arises in body cavity effusion without mass formation. Although there have been several case reports on HHV8-negative BCBL and the term "primary effusion lymphoma (PEL)-like lymphoma" has been coined, it is very rare and not defined in the current lymphoma classification. In those reports, HHV8-negative BCBL usually expresses B-cell markers and the prognosis seems to be better than those with HHV8-positive PEL with a few reports describing spontaneous regression of effusion. However, its clinicopathological features and prognosis remain unclear due to lack of retrospective study with sufficient number. [Method] We collected data of BCBL diagnosed between 1990 and 2014 from 42 institutions in Japan and clinicopathological features were retrospectively analyzed. We focused on clinicopathological features and prognosis of HHV8-negative BCBL, which was defined as HHV8-negative lymphoma that developed in body cavity effusion (pleural effusion, pericardial effusion, and ascites) without mass formation or extra-cavitary lesions at diagnosis. HHV8 status was assessed with immunohistochemical staining with anti-LANA-1 antibody (n=34) and/or polymerase chain reaction for HHV8 (n=31) of body-cavity effusion sample.Overall survival (OS), progression free survival (PFS), and time to progression (TTP) were calculated using Kaplan-Meier method. In patients without any systemic treatment for 3 months from diagnosis, failure of the first systemic treatment was considered as an event for PFS or TTP. [Results] Case report form of 71 patients with BCBL was collected. With central review, 4 patients did not meet the criteria of BCBL (existence of tumor mass or no objective evidence of lymphoma by morphology or immunophenotype) and 67 patients with BCBL were identified. Out of them, 50 and 6 were compatible with the diagnosis of HHV8-negative BCBL and PEL, respectively. In another 11 cases, HHV8 status could not be evaluated. In the 50 patients with HHV8-negative BCBL, male to female ratio was 1.3 : 1, and median age at the diagnosis was 76 years (57-98), HIV was negative in all of the 46 patients who were tested. Twenty-four patients (47%) had an underlying medical condition leading to fluid overload such as cirrhosis, cardiac disease, and renal dysfunction. Involved sites were pleural effusion (76%) followed by pericardial effusion (60%), and ascites (12%). Multiple sites were involved in 21 cases. The other clinical characteristics at the time of diagnosis were as follows: ECOG PS 0-1 (50%); B symptoms (14%); and elevated LDH (68%). Tumor cells expressed CD10 in 11/45 and CD20 in 48/50. Immunoglobulin light chain restriction was detected in 28/34. EBER in situ hybridization was positive in 4/32 (13%). The most common first-line systemic therapy was CHOP or CHOP-like with or without rituximab (n=38) followed by rituximab alone (n=2), rituximab with etoposide (n=2), and hyperCVAD/MA (n=1). One patient died within a month before initiating treatment, and five more patients had no systemic treatment at diagnosis for reasons such as comorbidity or frailty. Of the 43 patients treated with systemic therapy, the overall response rate was 98% with 70% achieving a complete remission. With a median follow up of 22 (0-147) months, 2-year OS, PFS, TTP of HHV8-negative BCBL was 83.6%, 76.8%, and 90.5%, respectively (Figure 1-3). Fifteen patients relapsed after achieving response: the same body-cavity effusion alone (n=7), different body-cavity effusion with or without the same site (n=2), intra- or extra-cavitary tumor mass formation (n=6). Eleven patients died and the causes of death were lymphoma (n=8) and others (n=3). Of the 5 patients without systemic treatment at diagnosis, systemic treatment was initiated in only 1 patient at 30 months due to re-emergence of effusion. The remaining 4 patients had had no systemic treatment for a median of 24 (5-147) months and 3 patients were alive without disease without any systemic therapy at last follow-up. [Conclusion] To the best of our knowledge, this is the largest retrospective study on HHV8-negative BCBL. HHV8-negative BCBL had distinct clinicopathological features from PEL. It affected HIV-negative elderly and the lymphoma cell was positive for B cell markers in most cases. Almost all of the patients responded to systemic treatment and its prognosis was favorable. Figure 1 Figure 1. Figure 2 Figure 2. Figure 3 Figure 3. Disclosures No relevant conflicts of interest to declare.