Clinical Significance of Cytomegalovirus Reactivation in Patients With Plasma Cell Dyscrasia Who Were Treated With Anti-CD38 Monoclonal Antibody: A Retrospective Analysis in a Single Institution.

INTRODUCTION: Anti-CD38 monoclonal antibodies (mAbs) have improved the prognosis of patients with plasma cell dyscrasia (PCD), but are also associated with increased infectious adverse events. Cytomegalovirus (CMV) is a common latent pathogen that is reactivated in immunocompromised individuals. Although CMV reactivation has mostly been reported after high-dose chemotherapy followed by stem cell transplantation in patients with PCD, cases of reactivation during anti-CD38 mAb therapy have been reported recently. Due to limited studies, we aimed to determine the frequency and impact of CMV reactivation during anti-CD38 mAb therapy. PATIENTS AND METHODS: This retrospective analysis included 154 consecutive patients with PCD who were treated with anti-CD38 mAbs at a single institution. RESULTS: Seventy-six patients were evaluated for CMV reactivation by CMV pp65 antigen testing, and 29 (38%) patients, including nine with newly diagnosed PCD, showed positive results. Patients who tested positive for the CMV pp65 antigen had substantially lower serum albumin levels than those who tested negative. However, the two groups showed no marked difference in the concurrent anti-PCD medications or baseline absolute lymphocyte count. Although most patients showing positive results in the CMV pp65 antigen test had mild or no symptoms, with fever being the most common symptom, some patients developed CMV end-organ disease. In addition, CMV reactivation interfered with the course of anti-PCD treatment in most patients, necessitating dose reductions, delays, and discontinuation of chemotherapy. CONCLUSION: This study provides an overview of the clinical impact of CMV reactivation in patients with PCD treated with anti-CD38 mAb-containing regimens.

ctDNA improves prognostic prediction in relapsed/refractory MM receiving ixazomib, lenalidomide, and dexamethasone.

It remains elusive how driver mutations, including those detected in circulating tumor DNA (ctDNA), affect prognosis in relapsed/refractory multiple myeloma (RRMM). Here we performed targeted-capture sequencing using bone marrow plasma cells (BMPC) and ctDNA of 261 RRMM cases uniformly treated with ixazomib, lenalidomide, and dexamethasone in a multicenter, prospective, observational study. We detected 24 and 47 recurrently mutated genes in BMPC and ctDNA, respectively. In addition to clonal hematopoiesis-associated mutations, varying proportion of driver mutations, particularly TP53 mutations (59.2% of mutated cases), were present in only ctDNA, suggesting their subclonal origin. In univariable analyses, ctDNA mutations of KRAS, TP53, DIS3, BRAF, NRAS, and ATM were associated with worse progression-free survival (PFS). BMPC mutations of TP53 and KRAS were associated with inferior PFS, while KRAS mutations were prognostically relevant only when detected in both BMPC and ctDNA. A total number of ctDNA mutations in the six relevant genes was a strong prognostic predictor (2-year PFS rates: 57.3%, 22.7%, and 0% for 0, 1, and ≥ 2 mutations, respectively) and independent of clinical factors and plasma DNA concentration. Using the number of ctDNA mutations, plasma DNA concentration, and clinical factors, we developed a prognostic index (ctRRMM-PI), classifying patients into three categories with 2-year PFS rates of 57.9%, 28.6%, and 0%. Serial analysis of ctDNA mutations in 94 cases revealed that TP53 and KRAS mutations frequently emerge after therapy. Thus, we clarify the genetic characteristics and clonal architecture of ctDNA mutations and demonstrate their superiority over BMPC mutations for prognostic prediction in RRMM.

Primary analysis of a prospective cohort study of Japanese patients with plasma cell neoplasms in the novel drug era (2016-2021).

The emergence of novel drugs has significantly improved outcomes of patients with plasma cell neoplasms (PCN). The Japanese Society of Hematology conducted a prospective observational study in newly diagnosed PCN patients between 2016 and 2021. The analysis focused on 1385 patients diagnosed with symptomatic PCN between 2016 and 2018. The primary endpoint was the 3-year overall survival (OS) rate among patients requiring treatment (n = 1284), which was 70.0% (95%CI 67.4-72.6%). Approximately 94% of these patients received novel drugs as frontline therapy. The 3-year OS rate was 90.3% (95%CI 86.6-93.1%) in the 25% of patients who received upfront autologous stem cell transplantation (ASCT), versus just 61.4% (95%CI 58.0-64.6%) in those who did not receive upfront ASCT. The only unfavorable prognostic factor that affected OS in ASCT recipients was an age of 65 or higher. For patients who did not receive ASCT, independent unfavorable prognostic factors included frontline treatment with conventional chemotherapies, international staging system score of 2/3, extramedullary tumors, and Freiberg comorbidity index of 2/3. This study unequivocally demonstrates that use of novel drugs improved OS in Japanese myeloma patients, and underscores the continued importance of upfront ASCT as the standard of care in the era of novel drugs.

A novel T cell-redirecting anti-GPRC5D × CD3 bispecific antibody with potent antitumor activity in multiple myeloma preclinical models.

G-protein-coupled receptor class 5 member D (GPRC5D) is detected in malignant plasma cells in approximately 90% of patients diagnosed with multiple myeloma (MM). Here, we constructed BsAb5003, a novel humanized bispecific monoclonal antibody targeting CD3 and GPRC5D, and evaluated its therapeutic impact on MM. BsAb5003 induced specific cytotoxicity of GPRC5D-positive MM cells with concomitant T cell activation and cytokine release. The efficacy of BsAb5003 was associated with GPRC5D expression levels in MM cell lines. Flow cytometry analysis of bone marrow mononuclear cells (BMMNCs) from 49 MM patients revealed that GPRC5D was expressed in a wide population of MM patients, including heavily treated and high-risk patients. In ex vivo assays using BMMNCs, BsAb5003 induced potent efficacy against CD138 + MM cells in both newly diagnosed and relapsed/refractory patient samples in a GPRC5D expression-dependent manner. BsAb5003 significantly enhanced T cell activation and cytokine production in combination with immunomodulatory drugs (IMiDs) against MM cell lines. BsAb5003 also demonstrated significant inhibition of in vivo tumor growth by recruiting T cells. Taken together, these results suggest that T cell-redirecting bispecific antibody targeting GPRC5D as monotherapy and combination therapy with IMiDs could be a highly potent and effective treatment approach for a wide population of MM patients.

Nomogram for predicting survival of patients with diffuse large B-cell lymphoma.

The international prognostic index (IPI) system has been widely used to predict prognosis in diffuse large B-cell lymphoma (DLBCL). However, this system categorizes DLBCL patients into four risk groups, and cannot optimize individualized prognosis. In addition, other clinicopathological factors, such as molecular aberrations, are not incorporated into the system. To partly overcome these weak points, we developed nomograms to predict individual patient survival. We also incorporated MYD88L265P and CD79BY196 mutations into the nomograms since these mutations are associated with a worse prognosis and their signaling pathways have been highlighted as a therapeutic target. We analyzed 302 DLBCL cases for which multivariate analysis by Cox proportional hazard regression was performed. Nomograms for progression-free survival (PFS) and overall survival (OS) were constructed and assessed by a concordance index (C-index). The nomograms were also evaluated using an open external dataset (n = 187). The MYD88L265P and/or CD79BY196 (MYD88/CD79B) mutation was detected in 62/302 patients. The nomograms incorporating IPI factors exhibited a C-index of 0.738 for PFS and a C-index of 0.765 for OS. The nomograms incorporating IPI factors and the MYD88/CD79B mutation showed a C-index of 0.745 for PFS and a C-index of 0.769 for OS. The nomograms we created were evaluated using an external dataset and were well validated. The present nomograms incorporating IPI factors and the MYD88/CD79B mutation have sufficient discrimination ability, and may effectively predict prognosis in DLBCL patients. The prognostic models we have presented here may help clinicians personalize prognostic assessments and clinical decisions.

Low-dose fluconazole as a useful and safe prophylactic option in patients receiving allogeneic hematopoietic stem cell transplantation.

BACKGROUND: Invasive fungal infections (IFIs) represent a potentially fatal complication in patients who undergo allogeneic hematopoietic stem cell transplantation (HSCT) if the initiation of therapy is delayed. Some guidelines recommend antifungal prophylaxis or preemptive therapy for these patients depending on the risk of IFIs following allogeneic HSCT. This retrospective study aimed to identify the group of patients who safely undergo allogeneic HSCT with low-dose fluconazole (FLCZ) prophylaxis (100 mg/day). METHODS: We retrospectively reviewed 107 patients who underwent their first allogeneic HSCT at Nagoya City University Hospital from January 1, 2010, to December 31, 2019. We analyzed the efficacy of low-dose FLCZ prophylaxis and investigated the relationship between major risk factors and antifungal prophylaxis failure (APF) within 100 days post-transplant. RESULTS: Of the 107 patients, 70 received low-dose FLCZ prophylaxis, showing a cumulative incidence of APF of 37.1% and a proven/probable IFI rate of 4.3%. There were no fungal infection-related deaths, including Aspergillus infections, in the FLCZ prophylaxis group. In a multivariable analysis, cord blood transplantation (CBT) (subdistribution hazard ratio (SHR), 3.55; 95% confidence interval (CI), 1.44-8.77; p = 0.006) and abnormal findings on lung CT before transplantation (SHR, 2.24; 95% CI, 1.02-4.92; p = 0.044) were independent risk factors for APF in the FLCZ prophylaxis group. CONCLUSION: Low-dose FLCZ prophylaxis is a useful and safe option for patients receiving allogeneic HSCT, except in those undergoing CBT or having any fungal risk features including history of fungal infections, positive fungal markers, and abnormal findings on lung CT before transplantation.

Involvement of cardiac glycosides targeting Na/K-ATPase in their inhibitory effects on c-Myc expression via its transcription, translation and proteasomal degradation.

Cardiac glycosides (CGs) have been used for decades to treat heart failure and arrhythmic diseases. Recent non-clinical and epidemiological findings have suggested that CGs exhibit anti-tumor activities. Therefore, CGs may be repositioned as drugs for the treatment of cancer. A detailed understanding of the anti-cancer mechanisms of CGs is essential for their application to the treatment of targetable cancer types. To elucidate the factors associated with the anti-tumor effects of CGs, we performed transcriptome profiling on human multiple myeloma AMO1 cells treated with periplocin, one of the CGs. Periplocin significantly down-regulated the transcription of MYC (c-Myc), a well-established oncogene. Periplocin also suppressed c-Myc expression at the protein levels. This repression of c-Myc was also observed in several cell lines. To identify target proteins for the inhibition of c-Myc, we generated CG-resistant (C9) cells using a sustained treatment with digoxin. We confirmed that C9 cells acquired resistance to the inhibition of c-Myc expression and cell proliferation by CGs. Moreover, the sequencing of genomic DNA in C9 cells revealed the mutation of D128N in α1-Na/K-ATPase, indicating the target protein. These results suggest that CGs suppress c-Myc expression in cancer cells via α1-Na/K-ATPase, which provides further support for the anti-tumor activities of CGs.

A prospective, multicenter, observational study of ixazomib plus lenalidomide-dexamethasone in patients with relapsed/refractory multiple myeloma in Japan.

Real-world studies permit inclusion of a more diverse patient population and provide more information on the effectiveness of treatments used in routine clinical practice. This prospective, multicenter, observational study investigated the effectiveness and safety of ixazomib plus lenalidomide and dexamethasone (IRd) in 295 patients with relapsed/refractory multiple myeloma (RRMM) in routine clinical practice in Japan. Patients had a median age of 74 years, 80.0% were aged ≥ 65 years, 42.0% had received ≥ 3 lines of prior treatment, and 28.5% were "frail" according to the International Myeloma Working Group frailty score. After a median follow-up of 25.0 months, median progression-free survival (PFS) was 15.3 (95% CI 12.4-19.5) months, while median overall survival was not reached. The overall response rate was 53.9%, and 31.5% of patients had a very good partial response or better. In the subgroup analysis, median PFS was better in patients with 1 versus 2 or ≥ 3 lines of prior treatment (29.0 vs 19.2 or 6.9 months) and paraprotein versus clinical relapse (16.0 vs 7.9 months), but median PFS was not notably affected by frailty score or age group. Dose adjustment was more frequent among patients aged > 75 years, especially early after IRd treatment initiation. Treatment-emergent adverse events (TEAEs) of any grade occurred in 84.4% of patients and 24.7% of patients discontinued treatment due to TEAEs; no new safety concerns were found. These findings suggest that oral IRd triplet regimen is an effective and tolerable treatment option for RRMM patients in real-world settings outside of clinical trials.ClinicalTrials.gov identifier: NCT03433001; Date of registration: 14 February 2018.

Safety, pharmacokinetics, and efficacy of belantamab mafodotin monotherapy in Japanese patients with relapsed or refractory multiple myeloma: DREAMM-11.

Belantamab mafodotin, a B-cell maturation antigen-targeting antibody-drug conjugate (ADC), was investigated in Japanese patients with relapsed/refractory multiple myeloma in Part 1 of the phase I DREAMM-11 study. Patients who had received ≥ 2 prior lines of therapy including a proteasome inhibitor and immunomodulatory agent were eligible. Eight patients received belantamab mafodotin monotherapy at 2.5 mg/kg (n = 4) or 3.4 mg/kg (n = 4) by intravenous infusion every 3 weeks on day 1 of each cycle until disease progression or unacceptable toxicity. Primary objectives were tolerability and safety, and secondary objectives included pharmacokinetics (PK) and efficacy. The most common Grade ≥ 3 adverse event was thrombocytopenia/platelet count decreased (2.5 mg/kg cohort, 100% [4/4]; 3.4 mg/kg cohort, 75% [3/4]), and no dose-limiting toxicities were observed. Ocular events, including keratopathy findings, were observed in most patients (2.5 mg/kg cohort, 100% [4/4]; 3.4 mg/kg cohort, 75% [3/4]) and were managed with dose modifications. All resolved within the study period. Overall response rates were 50% (2/4) in the 2.5 mg/kg cohort and 25% (1/4) in the 3.4 mg/kg cohort. Although PK profiles in Japanese patients varied, individual exposures overlapped with previous results in Western populations. Belantamab mafodotin monotherapy was generally well-tolerated and demonstrated clinical activity at both doses.

Integrated analysis of phase 1a and 1b randomized controlled trials; Treg-targeted cancer immunotherapy with the humanized anti-CCR4 antibody, KW-0761, for advanced solid tumors.

INTRODUCTION: Regulatory T cells (Tregs) have attracted attention as a novel therapeutic target to augment the clinical efficacy of immunotherapy. We conducted phase Ia and Ib trials to examine the safety and efficacy of the anti-CCR4 antibody, KW-0761 (mogamulizumab), which may eliminate effector Tregs (eTregs). We herein overviewed the results of these trials, presented cases with a durable clinical response, and investigated factors associated with the clinical effects of KW-0761. METHODS: Forty-nine patients with CCR4-negative solid cancers were enrolled in the phase Ia and Ib trials on KW-0761. An integral analysis of safety, clinical responses, prognosis, blood laboratory data, and cancer testis antigen-specific immune responses was performed. RESULTS: Grade 3-4 treatment-related adverse events were reported in 21 (42.9%) out of 49 patients, all of which were manageable. A partial response and stable disease were observed in 1 and 9 patients, respectively. A durable clinical response was noted in 2 esophageal and 2 lung cancer patients. eTreg depletion in peripheral blood was confirmed in most patients, and eTreg depletion was sustained during the KW-0761 treatment. High lymphocyte levels at baseline and 2 weeks after the initiation of KW-0761 were associated with a favorable clinical outcome. CONCLUSIONS: A durable clinical response was noted in some patients, and high lymphocyte levels before treatment initiation may be a biomarker for the efficacy of KW-0761. The synergistic effect of KW-0761 for depleting Tregs and other immunotherapies is expected in the future.

Risk factors associated with overall survival in patients with multiple myeloma following carfilzomib treatment: A retrospective study from a large claims database in Japan.

BACKGROUND: Carfilzomib is a selective proteasome inhibitor approved for treating relapsed or refractory multiple myeloma (RRMM). Carfilzomib improves overall survival (OS) and progression-free survival (PFS); however, treatment with carfilzomib results in a higher incidence of cardiovascular and renal toxicity. More than 70% of patients with RRMM in clinical practice do not meet the eligibility criteria for randomized clinical trials (RCT). OS and PFS are negatively influenced by complications, concomitant medications and prior treatments. Therefore, we assessed the risk factors influencing the OS and time to next treatment (TTNT) in the real world. TTNT has emerged as a relevant alternative clinical endpoint to PFS. METHODS: A retrospective analysis of a large claims database prepared during the post-marketing stages in Japan was performed. The patients treated with carfilzomib for the first time were identified. Multivariable Cox proportional hazards regression analysis was performed to evaluate the risk factors influencing OS and TTNT following carfilzomib treatment. RESULTS: A total of 732 patients with RRMM who received carfilzomib-containing chemotherapy between April 2014 and September 2021 were identified. Multivariable Cox regression analysis for OS and TTNT showed a significantly higher hazard ratio (HR) of 1.48 (95% confidence interval [Cl]: 1.10-2.00; p = 0.010) and 1.38 (95% Cl: 1.15-1.65; p < 0.001), respectively, for patients with renal impairment compared to those without renal impairment. Multivariable Cox regression analysis for OS and TTNT showed a significantly higher HR of 1.80 (95% Cl: 1.27-2.55; p = 0.0010) and 1.38 (95% Cl: 1.14-1.66; p < 0.001), respectively, for patients with prior lenalidomide treatment compared to those without prior lenalidomide treatment. CONCLUSION: Complication of renal impairment and prior lenalidomide treatment could be risk factors influencing OS and TTNT during carfilzomib treatment.

Elranatamab in relapsed or refractory multiple myeloma: phase 2 MagnetisMM-3 trial results.

Elranatamab is a humanized B-cell maturation antigen (BCMA)-CD3 bispecific antibody. In the ongoing phase 2 MagnetisMM-3 trial, patients with relapsed or refractory multiple myeloma received subcutaneous elranatamab once weekly after two step-up priming doses. After six cycles, persistent responders switched to biweekly dosing. Results from cohort A, which enrolled patients without prior BCMA-directed therapy (n = 123) are reported. The primary endpoint of confirmed objective response rate (ORR) by blinded independent central review was met with an ORR of 61.0% (75/123); 35.0% ≥complete response. Fifty responders switched to biweekly dosing, and 40 (80.0%) improved or maintained their response for ≥6 months. With a median follow-up of 14.7 months, median duration of response, progression-free survival and overall survival (secondary endpoints) have not been reached. Fifteen-month rates were 71.5%, 50.9% and 56.7%, respectively. Common adverse events (any grade; grade 3-4) included infections (69.9%, 39.8%), cytokine release syndrome (57.7%, 0%), anemia (48.8%, 37.4%), and neutropenia (48.8%, 48.8%). With biweekly dosing, grade 3-4 adverse events decreased from 58.6% to 46.6%. Elranatamab induced deep and durable responses with a manageable safety profile. Switching to biweekly dosing may improve long-term safety without compromising efficacy. ClinicalTrials.gov identifier: NCT04649359 .

The Relationship between Changes in Serum Element Concentrations and Pathological Condition and Disease Status in Japanese Multiple Myeloma Patients: A Pilot Study and Literature Review.

BACKGROUND: Multiple myeloma (MM) is a rare cancer, and information on its pathological condition and serum element levels is lacking. In this pilot study, we examined serum element concentrations in Japanese patients with MM by a comprehensive multi-element analysis. METHODS: This is a case-control study of 12 Japanese patients diagnosed with MM at the Nagoya City University Hospital between 2008 and 2013. Blood samples were taken, at the initial diagnosis and at relapse. The serum concentrations of 12 elements were analyzed by inductively coupled plasma mass spectrometry and compared between MM patients and non-MM volunteers. We also analyzed the correlation between serum element concentrations and laboratory values related to disease status and tumor volume of MM. RESULTS: We found that serum chromium (Cr), copper (Cu), molybdenum (Mo), and barium (Ba) concentrations were significantly increased in MM patients. Ba was significantly increased in MM patients, suggesting an association with bone lesions. There was no consistent trend between these elements and existing indices related to MM tumor volume and disease status. CONCLUSIONS: Although this is a pilot study, serum Cr, Cu, Mo, and Ba concentrations were found to be significantly elevated in MM patients. Further studies with large sample sizes are needed, since the changes in serum concentrations of these elements may reflect the pathological condition of MM.

A retrospective analysis of clinical features and treatment outcome in 21 patients with immunoglobulin M-related light-chain amyloidosis in Japan: a study from the Amyloidosis Research Committee.

We retrospectively gathered data of 21 patients (13 male and 8 female; median age 65 years) diagnosed with immunoglobulin M (IgM)-related light-chain (AL) amyloidosis in Japan to investigate characteristics of IgM-AL amyloidosis and its optimal treatment strategy. Median IgM and difference free light chain (FLC) at diagnosis were 1257 mg/dl and 34.3 mg/l, respectively. Organ involvement was observed in the heart in 7 patients (33%), kidneys in 15 (71%), and lymph nodes in 5 (24%). Initial treatments were melphalan/dexamethasone in 7 patients, bortezomib/cyclophosphamide/dexamethasone in 3, autologous stem cell transplantation in 3, rituximab/bendamustine in 1, other in 3, and none in 4. Hematological responses among 15 evaluable patients were as follows: 3 reached complete response (CR), 4 partial response (PR), and 1 very good PR (VGPR), making the overall response rate of PR or better 40%. Median overall survival (OS) was 14.0 months and 1-year OS was 71.4%. Prognosis was significantly poorer in patients with cardiac involvement than those with non-cardiac involvement (1-year OS 27.8% vs. 85.7%, p = 0.0468). The involved FLC value was low in several patients and therapeutic response was difficult to assess. Further study is necessary to determine the optimal treatment for IgM-AL amyloidosis.

Laryngeal edema as a symptom of local cytokine release syndrome after BCMA-targeting CAR-T therapy for relapsed and refractory multiple myeloma.

Cytokine release syndrome (CRS) can be a major side effect of chimeric antigen receptor T-cell (CAR-T) therapy, and may occasionally become life-threatening in patients with factors such as high tumor burden or poor performance status. Among the many CRS events observed in B-cell maturation antigen (BCMA)-targeting CAR-T therapy, local symptoms (also called local CRS) are poorly understood due to their low frequency. Here, we present the case of a 54-year-old woman with refractory multiple myeloma exhibiting laryngeal edema as a local CRS. Before CAR-T therapy, she was diagnosed with progressive disease indicated by a left thyroid mass. After local irradiation, she received the BCMA-targeting CAR-T agent idecabtagene vicleucel (ide-cel). On day 2, the patient developed CRS, which resolved on treatment with tocilizumab. However, on day 4, laryngeal edema worsened, and was judged to be a local CRS. Intravenous dexamethasone rapidly reduced this edema. In conclusion, laryngeal edema rarely occurs as a local CRS, and to the best of our knowledge, has never been reported after ide-cel infusion. Dexamethasone was effective for reducing the local reaction that persisted after treatment of systemic symptoms with tocilizumab.

Changing trends in the risk factors for second primary malignancies after autologous stem cell transplantation for multiple myeloma before and after the introduction of proteasome inhibitors and immunomodulatory drugs.

The incidence of second primary malignancies (SPM) in long-term survivors of multiple myeloma (MM) is increasing because of increased life expectancy. We retrospectively analyzed the risk factors for SPM in patients with MM after autologous stem cell transplantation (ASCT) before and after the introduction of proteasome inhibitors and immunomodulatory drugs (IMiDs). In total, 2,340 patients newly diagnosed with MM who underwent ASCT between 1995 and 2016 were enrolled in this study. Forty-three patients developed SPM (29 solid, 12 hematological, and 2 unknown tumors), with cumulative incidence rates of 0.8% and 2.5% at 24 and 60 months, respectively. The cumulative incidence rates of hematological and solid SPM at 60 months were 0.8% and 1.8%, respectively. The overall survival (OS) rate at 60 months after ASCT was 62.9% and the OS rates after the diagnosis of SPM at 24 months were 72.2% for hematological SPM and 70.9% for solid SPM. Multivariate analysis revealed that the use of IMiDs (P=0.024) and radiation (P=0.002) were significant independent risk factors for SPM. The probabilities of developing SPM and death due to other causes (mainly MM) at 60 months were 2.5% and 36.5%, respectively, indicating that the risk of SPM was lower than that of death from MM. Furthermore, SPM between the pre-novel and novel agent eras (ASCT between 2007 and 2016) groups significantly increased (1.9% vs. 4.3% at 60 months; P=0.022). The early occurrence of SPM after ASCT should be monitored cautiously.

The hepatic niche leads to aggressive natural killer cell leukemia proliferation through the transferrin-transferrin receptor 1 axis.

Aggressive natural killer cell leukemia (ANKL) is a rare lymphoid neoplasm frequently associated with Epstein-Barr virus, with a disastrously poor prognosis. Owing to the lack of samples from patients with ANKL and relevant murine models, comprehensive investigation of its pathogenesis including the tumor microenvironment (TME) has been hindered. Here we established 3 xenograft mice derived from patients with ANKL (PDXs), which enabled extensive analysis of tumor cells and their TME. ANKL cells primarily engrafted and proliferated in the hepatic sinusoid. Hepatic ANKL cells were characterized by an enriched Myc-pathway and proliferated faster than those in other organs. Interactome analyses and in vivo CRISPR-Cas9 analyses revealed transferrin (Tf)-transferrin receptor 1 (TfR1) axis as a potential molecular interaction between the liver and ANKL. ANKL cells were rather vulnerable to iron deprivation. PPMX-T003, a humanized anti-TfR1 monoclonal antibody, showed remarkable therapeutic efficacy in a preclinical setting using ANKL-PDXs. These findings indicate that the liver, a noncanonical hematopoietic organ in adults, serves as a principal niche for ANKL and the inhibition of the Tf-TfR1 axis is a promising therapeutic strategy for ANKL.