Abstract: Introduction: Adult T-cell leukemia/lymphoma (ATLL) is a peripheral T-cell lymphoma that is caused by HTLV-1. The prognosis of acute and lymphomatous variants of ATLL is poor, ranging from 2 weeks to 〉 1 year. Compared to other types of malignant lymphomas, the organ infiltration is frequently observed in ATLL (Yamada et al. Leuk Lymphoma 1997). We previously reported the landscape of genetic mutations in ATLL, and showed that various mutations occurred in the TCR-NFκB pathway in more than 90% of ATLL cases (Kataoka et al. Nat Genet 2015). These somatic mutations are thought to develop ATLL in combination with viral genes such as HTLV-1 bZIP factor (HBZ). Among them, mutations in TET2, an epigenetic regulator, was observed in about 10% of ATLL cases. Higher frequencies inTET2 mutation was reported in other types of peripheral T-cell lymphoma (PTCL); it was observed in about 80% of angioimmunoblastic T-cell lymphoma (AITL) and in about 50% of PTCL, not otherwise specified. In PTCL, it has been reported that additional mutations in lymphoid progenitors derived from TET2 mutated hematopoietic stem cells cause increased cell proliferation and anti-apoptosis, leading to the disease progression. In ATLL, the role of TET2 mutation in disease progression is still unknown. In this study, we investigated the role of TET2 mutation in ATLL using mouse model and acute and lymphomatous variant ATLL cohort. Materials and methods: As an animal model of HTLV-1 infection or ATLL, transgenic mice expressing HBZ under the control of the mouse CD4 promoter (HBZ-Tg) were generated with C57BL/6 background. Heterozygous TET2 knock-down mice (TET2KD) were generated with C57BL/6 background by gene trapping (Tang et al. Transgenic Res 2008; Shide et al. Leukemia 2012). HBZ-Tg/TET2KD compound mice (double mutant) were generated by crossing them. HBZ-Tg, TET2KD, and double mutant mice were investigated by cell counts, organ weight, FACS analysis, pathological analysis, and survival analysis. The relationship between the TET2 mutation status and the clinical feature was investigated using our acute and lymphomatous variant ATLL cohort (n=115). Result: At 12 months, compared to wild type mouse (WT), sporadic splenomegaly and lymphadenopathy were observed in HBZ-Tg. No significant increase was observed in peripheral blood (PB) leukocyte and mononuclear cell (MNC) of BM and spleen, but an increase was observed in the estimated whole body MNC (Femur x 100/6 + spleen) (WT vs. HBZ-Tg; estimated whole body MNC (x106 cells/body), 416±162 vs. 621±147, p=0.01). In FACS analysis, the frequency of CD4+ T-cell was increased in PB, spleen, and BM (WT vs. HBZ-Tg; PB-CD4+ T-cell%, 4.9±0.9 vs. 28.2±22.8, p 〈 0.05; spleen CD4+ T-cell%, 10.3±3.1 vs. 18.2±3.3, P 〈 0.01; BM-CD4+ T-cell%, 1.2±0.6 vs. 2.5±1.1, p 〈 0.05), and the estimated whole body CD4+ T-cell count was also increased (WT vs. HBZ-Tg; CD4+ T-cells (x106 cells/body) 13.6±7.6 vs. 41.9±24.4, p 〈 0.01). In the survival analysis, compared to WT, the shortened overall survival (OS) was observed in HBZ-Tg (median survival time (MST, month), unreached vs. 11.1, p 〈 0.01). In pathological analysis, HBZ-Tg showed increased leukocyte infiltration to various organs such as lung and liver, and the infiltrated cells were mainly composed of T-cells. In the lung, in addition to the cell infiltration, alveolar edema was observed, which was presumed to be the main cause of death. Next, to elucidate the role of TET2 mutation in ATLL, the double mutant was analyzed. At six months, compared to HBZ-Tg, no increase was observed in the number of PB leukocyte, spleen-MNC, and BM-MNC, and also in the frequency and the number of CD4+ T-cells in PB, spleen and BM. However, in pathological and survival analysis, the double mutant showed severe cell infiltration in lung and liver and demonstrated inferior OS (median OS (month), 11.1 vs. 6.0, p 〈 0.05). Further, the double mutant showed increased frequency of CD103 (integrin alpha E), an adhesion molecule, expressing cells (CD4+CD103+% in spleen; 6.7±1.0 vs. 10.9±1.9, p 〈 0.05). In the acute and lymphomatous variant ATLL cohort analysis, genetic and clinical investigation revealed that organ infiltration detectable by imaging studies was frequently observed in TET2 mutated patients (WT-Pt (n=100) vs. TET2 mutated-Pt (n=15); extra nodular lesion, 78/100 vs. 14/15). Conclusion: In both mice model and human cohort, TET2 mutation exacerbated organ infiltration of ATLL cells. Disclosures No relevant conflicts of interest to declare.

Abstract: Adult T-cell leukemia/lymphoma (ATL) is an aggressive T-cell malignancy with a dismal prognosis, caused by HTLV-1. Although our previous study, mainly using whole-exome sequencing and SNP array karyotyping, discovered many driver mutations and copy number alterations (CNAs), the whole-genome landscape of ATL still remains elusive. To this end, we have performed high-depth whole-genome sequencing (WGS) of 155 ATL cases with a median sequencing depth of 96-fold for tumors. Among them, 75 cases were also analyzed by RNA sequencing (RNA-seq). In total, we detected 1,952,490 single nucleotide variants (SNVs) and 159,141 insertion-deletions (4.0 SNVs and 0.3 indels/Mb/case), 10,279 SVs (66.3 SVs/case), and 3,975 CN altered segments (25.7 segments/case). Using several driver discovery algorithms (dNdScv, MutSig2CV, and DriverPower), we identified 47 significantly mutated genes, 19 of which were mutated in more than 10% of cases. These included several novel mutations, such as those affecting XPO1 (7.1%), ZNF292 (6.5%), and ITGB1 (5.2%). Using GISTIC2.0, we identified 13 significant CNAs, such as IRF4 amplifications and CDKN2A deletions, consistent with previous SNP array data. To detect significantly recurrent SVs, we calculated SV breakpoint frequency and identified 13 genes affected by SVs, including the previously identified genes (such as CARD11, CD274, and TP73). In addition, we investigated recurrent mutations in non-coding elements by DriverPower and LARVA and discovered 12 recurrently mutated elements. Among them, the most frequent were splice site mutations, including those of HLA-A and HLA-B, most of which caused loss of function as revealed by RNA-seq. By contrast, we found recurrent mutations in TP73 splice site, which induced skipping of exons 2 and 3, generating a dominant-negative variant similar to their SVs. In addition, recurrent non-coding elements contained several novel regions, such as 3´-untranslated region (UTR) of NFKBIZ and 5´- UTR of TMSB4X. Altogether, a total of 56 genes were recurrently altered. The median number of driver alterations was eight per case, and at least one driver alteration was found in 149 cases (96.1%). Among 56 driver genes, 40 (71.4%) genes were affected by more than one alteration class. Some drivers, such as CDKN2A, IKZF2, and CD274, were affected almost exclusively by CNAs and/or SVs, while showing quite high alteration frequencies (11.6-29.0%). These observations suggest that WGS presented a substantially different overview of driver alterations from our previous study. The overall numbers of mutations and SVs were linked to these driver alterations, suggesting their etiology. In particular, inactivation of EP300 and immune-related molecules, such as HLA-A, HLA-B, and CD58, were associated with an increased number of mutations and SVs, especially deletions and tandem duplications. By contrast, cases with TP53-altered cases harbored more inversions and translocations. These results emphasize a pivotal role of immune evasion for acquiring genetic alterations to drive ATL progression. To define molecular subgroups in ATL, we integrated the 56 identified genetic drivers using non-negative matrix factorization clustering and identified two robust subgroups with discrete clinical and genetic characteristics. Group 1 was enriched with alterations affecting distal components of T-cell receptor (TCR)/NF-κB signaling (such as CARD11, PRKCB, and IRF4) and immune-related molecules (HLA-A, HLA-B, and CD58), whereas proximal regulators of TCR/NF-κB signaling (PLCG1, VAV1, and CD28) and a JAK/STAT signaling molecule (STAT3) were more frequently altered in group 2. In addition, group 1 cases had a larger number of mutations, SVs, and CNAs than group 2 cases. Clinically, most cases with lymphoma subtype were classified into group 1, whereas group 2 mainly consisted of cases with leukemic subtypes. Moreover, group1 cases showed a worse overall survival than group 2, independently of clinical subtype. These results suggest the biological and clinical relevance of the molecular classification of ATL. In summary, our WGS analysis not only identifies novel somatic alterations but also extends the overview of ATL genome. We also propose a new molecular classification of ATL, with its clinical relevance, which can lead to the future improvement of patient management. Disclosures Kogure: Takeda Pharmaceutical Company Limited.: Honoraria. Nosaka:Kyowa Kirin Co.Ltd: Honoraria; Chugai pharmaceutical Co. Ltd: Honoraria; Novartis international AG: Honoraria; Celgene K.K: Honoraria; Eisai Co., Ltd: Honoraria; Merck Sharp & Dohme K.K.: Honoraria; Bristol-Myer Squibb: Honoraria. Imaizumi:Kyowa Kirin Co. Ltd.: Honoraria; Bristol-Myers Squibb: Honoraria; Celgene: Honoraria; Eisai: Honoraria. Utsunomiya:Kyowa Kirin: Honoraria; Celgene: Honoraria. Shah:Celgene: Research Funding; BMS: Research Funding; Physicians Education Resource: Honoraria. Janakiram:Takeda, Fate, Nektar: Research Funding. Ramos:NIH: Research Funding. Takaori-Kondo:Astellas Pharma: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Bristol-Myers Squibb: Honoraria, Research Funding; Kyowa Kirin: Honoraria, Research Funding; Ono Pharmaceutical: Research Funding; Thyas Co. Ltd.: Research Funding; Takeda: Research Funding; CHUGAI: Research Funding; Eisai: Research Funding; Nippon Shinyaku: Research Funding; Otsuka Pharmaceutical: Research Funding; Pfizer: Research Funding; OHARA Pharmaceutical: Research Funding; Sanofi: Research Funding; Novartis Pharma: Honoraria; MSD: Honoraria. Miyazaki:Sumitomo Dainippon Pharma Co., Ltd.: Honoraria; Kyowa Kirin Co., Ltd.: Honoraria; Chugai Pharmaceutical Co., Ltd.: Honoraria; Celgene: Honoraria; NIPPON SHINYAKU CO.,LTD.: Honoraria; Otsuka Pharmaceutical: Honoraria; Novartis Pharma KK: Honoraria; Astellas Pharma Inc.: Honoraria. Matsuoka:Chugai Pharmaceutical Co. Ltd: Research Funding; Bristol-Myers Squibb: Research Funding; Kyowa Kirin Co. Ltd.: Research Funding. Ishitsuka:Takeda: Other: Personal fees, Research Funding; mundiharma: Other: Personal fees; Taiho Pharmaceuticals: Other: Personal fees, Research Funding; Janssen Pharmaceuticals: Other: Personal fees; Novartis: Other: Personal fees; Pfizer: Other: Personal fees; Astellas Pharma: Other, Research Funding; Genzyme: Other; Sumitomo Dainippon Pharma: Other, Research Funding; Eisai: Other, Research Funding; Mochida: Other, Research Funding; Shire: Other; Otsuka Pharmaceutical: Other; Ono Pharmaceutical: Other, Research Funding; Teijin Pharma: Research Funding; MSD: Research Funding; Asahi kasei: Research Funding; Eli Lilly: Research Funding; Daiichi Sankyo: Other; Huya Japan: Other; Celgene: Other: Personal Fees; Kyowa Hakko Kirin: Other: Personal fees, Research Funding; BMS: Other: Personal fees; Chugai Pharmaceutical: Other: Personal fees, Research Funding. Ogawa:Asahi Genomics Co., Ltd.: Current equity holder in private company; Chordia Therapeutics, Inc.: Membership on an entity's Board of Directors or advisory committees, Research Funding; KAN Research Institute, Inc.: Membership on an entity's Board of Directors or advisory committees, Research Funding; Sumitomo Dainippon Pharma Co., Ltd.: Research Funding; Otsuka Pharmaceutical Co., Ltd.: Research Funding; Eisai Co., Ltd.: Research Funding. Shimoda:Takeda Pharmaceutical Company: Honoraria; Bristol-Myers Squibb: Honoraria; Shire plc: Honoraria; Celgene: Honoraria; Perseus Proteomics: Research Funding; PharmaEssentia Japan: Research Funding; AbbVie Inc.: Research Funding; Astellas Pharma: Research Funding; Merck & Co.: Research Funding; CHUGAI PHARMACEUTICAL CO., LTD.: Research Funding; Kyowa Hakko Kirin Co., Ltd.: Research Funding; Pfizer Inc.: Research Funding; Otsuka Pharmaceutical: Research Funding; Asahi Kasei Medical: Research Funding; Japanese Society of Hematology: Research Funding; The Shinnihon Foundation of Advanced Medical Treatment Research: Research Funding; Novartis: Honoraria, Research Funding. Kataoka:CHUGAI PHARMACEUTICAL CO., LTD.: Research Funding; Takeda Pharmaceutical Company: Research Funding; Otsuka Pharmaceutical: Research Funding; Asahi Genomics: Current equity holder in private company.

Abstract: The prognosis of aggressive adult T-cell leukemia/lymphoma (ATL) is poor, and allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a curative treatment. In order to identify favorable prognostic patients after intensive chemotherapy, and who therefore might not require upfront allo-HSCT, we aimed to improve risk stratification of aggressive ATL patients aged 〈 70 years. The clinical risk factors and genetic mutations were incorporated into risk modeling for overall survival (OS). We generated the m7-ATLPI, a clinicogenetic risk model for OS, that included the ATL prognostic index (PI) (ATL-PI) risk category, and non-silent mutations in seven genes, namely TP53, IRF4, RHOA, PRKCB, CARD11, CCR7, and GATA3. In the training cohort of 99 patients, the m7-ATLPI identified a low-, intermediate-, and highrisk group with 2-year OS of 100%, 43%, and 19%, respectively (hazard ratio [HR] =5.46; P 〈 0.0001). The m7-ATLPI achieved superior risk stratification compared to the current ATL-PI (C-index 0.92 vs. 0.85, respectively). In the validation cohort of 84 patients, the m7-ATLPI defined low-, intermediate-, and high-risk groups with a 2-year OS of 81%, 30%, and 0%, respectively (HR=2.33; P=0.0094), and the model again outperformed the ATL-PI (C-index 0.72 vs. 0.70, respectively). The simplified m7-ATLPI, which is easier to use in clinical practice, achieved superior risk stratification compared to the ATLPI, as did the original m7-ATLPI; the simplified version was calculated by summing the following: high-risk ATL-PI category (+10), low-risk ATL-PI category (−4), and non-silent mutations in TP53 (+4), IRF4 (+3), RHOA (+1), PRKCB (+1), CARD11 (+0.5), CCR7 (−2), and GATA3 (−3).

Abstract: Adult T-cell leukemia/lymphoma (ATL) is an aggressive neoplasm immunophenotypically resembling regulatory T cells, associated with human T-cell leukemia virus type-1. Here, we performed whole-genome sequencing (WGS) of 150 ATL cases to reveal the overarching landscape of genetic alterations in ATL. We discovered frequent (33%) loss-of-function alterations preferentially targeting the CIC long isoform, which were overlooked by previous exome-centric studies of various cancer types. Long but not short isoform–specific inactivation of Cic selectively increased CD4+CD25+Foxp3+ T cells in vivo. We also found recurrent (13%) 3′-truncations of REL, which induce transcriptional upregulation and generate gain-of-function proteins. More importantly, REL truncations are also common in diffuse large B-cell lymphoma, especially in germinal center B-cell–like subtype (12%). In the non-coding genome, we identified recurrent mutations in regulatory elements, particularly splice sites, of several driver genes. In addition, we characterized the different mutational processes operative in clustered hypermutation sites within and outside immunoglobulin/T-cell receptor genes and identified the mutational enrichment at the binding sites of host and viral transcription factors, suggesting their activities in ATL. By combining the analyses for coding and noncoding mutations, structural variations, and copy number alterations, we discovered 56 recurrently altered driver genes, including 11 novel ones. Finally, ATL cases were classified into 2 molecular groups with distinct clinical and genetic characteristics based on the driver alteration profile. Our findings not only help to improve diagnostic and therapeutic strategies in ATL, but also provide insights into T-cell biology and have implications for genome-wide cancer driver discovery.

Abstract: 7504 Background: No standard of care for elderly patients with aggressive adult T-cell leukemia/lymphoma (ATL) has been established yet. We assessed the efficacy of an anti-CCR4 antibody, mogamulizumab (Moga) combined with biweekly cyclophosphamide (CPA), doxorubicin (DXR), vincristine (VCR), and prednisone (PSL) (Moga-CHOP-14) for untreated elderly patients with aggressive ATL. Methods: In this phase 2 trial conducted at 21 centers in Japan, untreated CCR4-positive aggressive ATL patients aged 66 years or older and 56-65 years who were not candidates for allogeneic hematopoietic stem cell transplantation (allo-HSCT) received six cycles of Moga-CHOP-14, followed by two cycles of Moga monotherapy. The primary endpoint was 1-year progression-free survival (PFS), defined as the time from enrollment to the progression/relapse of ATL or death due to any cause, whichever occurred first. Secondary endpoints were complete response rate (CR), overall response rate (ORR), overall survival (OS), 1-year event-free survival (EFS), and the incidence of adverse events. The necessary number of patients calculated by setting the threshold 1-year PFS at 16% and the expected 1-year PFS at 31% using the exact method based on binomial distribution under the conditions of one-sided level of significance of 5% (α = 0.05) and power of 70% was 43. Results: A total of 50 patients were enrolled from October 2015, until September 2020. Among the 48 evaluable patients, the median age was 74 years (interquartile range [IQR], 70-78). ATL subtypes included 31, 9, and 8 patients for the acute, lymphoma, and unfavorable chronic type, respectively. ATL-PI included 9, 31, and 8 patients for high, intermediate, and low risk, respectively. With a median follow-up of 1.6 years (IQR, 0.7-2.4), 1-year PFS was 36.2% (90% confidence interval (CI), 24.9-47.6), and a median PFS was 0.7 years (95% CI, 0.5-1.0). CR and ORR were noted in 64.6% (95%CI, 49.5-77.8), and 91.7% (95% CI, 80.0-97.7), respectively. One-year OS was 66.0% (95% CI, 50.6-77.6) and median OS was 1.6 years (95%CI, 1.1-2.8). One-year EFS was 29.9% (95% CI, 17.6-43.2) and median EFS was 0.5 years (95%CI, 0.4-0.7). The most frequent adverse events grades 3/4, which occurred in 〉 10% of patients were lymphocytopenia (97.9%), leukopenia (93.8%), neutropenia (89.6%), febrile neutropenia (64.8%), anemia (58.3%), thrombocytopenia (45.8%), infection (27.1%), skin rash (20.8%), and hyperglycemia (20.8%). Relative dose intensity (RDI) was calculated for each drug: the mean RDI for Moga was 82.1%, for CPA 71.7%, for DXR 72.7%, for VCR 72.0%, and for PSL 77.3%. Conclusions: This study demonstrated that Moga-CHOP-14 significantly improved PFS in elderly patients with aggressive CCR4-positive ATL who were ineligible for allo-HSCT. Moga-CHOP-14 is now considered for the preferred first-line treatment in those patients. Clinical trial information: jRCTs041180130 .

Abstract: The efficacy of mogamulizumab in adult T‐cell leukemia/lymphoma ( ATLL ) was reported in a previous phase 2 study. Compared with patients in clinical trials, however, most patients in real‐life settings have demonstrated worse outcomes. Method We retrospectively analyzed 96 patients with relapsed/refractory ATLL who received mogamulizumab treatment. Results Relapsed/refractory ATLL patients with a median age of 70 years received a median of five courses of mogamulizumab. Hematologic toxicity and skin rash were the most common adverse events, and both were manageable. Of 96 patients, 87 were evaluable for efficacy. The overall response rate was 36%, and the median progression‐free survival ( PFS ) and overall survival ( OS ) from the start of mogamulizumab therapy were 1.8 and 4.0 months, respectively. Of the original 96 patients, only 25 fulfilled the inclusion criteria of the phase 2 study. Those who met the criteria demonstrated longer median PFS and OS durations of 2.7 and 8.5 months, respectively. The median OS from diagnosis in relapsed/refractory ATLL patients receiving mogamulizumab was 12 months, longer than the 5.8 months in a historical cohort without mogamulizumab. Conclusion In clinical practice, mogamulizumab exhibited antitumor activity in patients with relapsed/refractory ATLL , with an acceptable toxicity profile. Mogamulizumab therapy improved the OS of ATLL patients.

Abstract: Undifferentiated pleomorphic sarcoma (UPS) is a malignant soft tissue tumor that has been reclassified from malignant fibrous histiocytoma with the development of the pathological diagnosis. It principally occurs in the extremities but rarely occurs in the rectum. We herein report a rare case of UPS arising in the rectum. Case presentation A 85-year-old woman was referred to our hospital with a complaint of anal pain, which had persisted for several months. Computed tomography (CT) showed a 53 × 58 × 75 mm mass on the left side of the rectum. Colonoscopy revealed a submucosal elevation in the rectum without any exposure of the tumor to the surface. Contrast-enhanced CT and magnetic resonance imaging revealed an 80-mm mass that originated in the rectal muscular propria, and we suspected a gastrointestinal stromal tumor. No lymph node metastasis or distant metastasis was observed. We performed a laparoscopic Hartmann’s operation. Intraoperatively, severe adhesion around the tumor caused tumor injury and right ureteral dissection. Thus, laparoscopic right ureteral anastomosis and ureteral stenting were additionally performed. The operation time was 6 h and 3 min, and the estimated blood loss was small. The patient was discharged without complications 25 days after surgery. A pathological examination showed that the tumor was composed of highly heterogeneous cells with no specific differentiation traits, leading to a diagnosis of UPS. Contrast-enhanced CT performed 2 months after surgery showed bilateral pelvic lymph node enlargement, which indicated recurrence. Considering the patient’s age, we performed radiotherapy (50 Gy/25 Fr targeting the pelvic region). At present, 16 months have passed since the completion of radiotherapy. Contrast-enhanced CT shows that the recurrent lymph nodes have disappeared, and no new distant metastasis has been observed. Conclusions We reported a case of UPS arising in the rectum. The surgical procedure and indication of preoperative therapy should be carefully selected because complete removal of the tumor is desirable in UPS.