Subset Of B-cell Lymphomas Research Articles

Sgr-1505 Is a Potent MALT1 Protease Inhibitor with a Potential Best-in-Class Profile

Background: MALT1 (Mucosa-associated lymphoid tissue lymphoma translocation protein 1) is a component of the MALT1-BCL10-CARD11 complex downstream from the Bruton Tyrosine Kinase (BTK) on the B-cell receptor signaling pathway. MALT1 is a key mediator of nuclear factor kappa B (NF-κB) signaling, which is the main driver of a subset of B-cell lymphomas. MALT1 is considered a potential therapeutic target for several subtypes of non-Hodgkin B-cell lymphomas and chronic lymphocytic leukemia (CLL), including tumors with acquired BTK inhibitor (BTKi) resistance. Constitutive activation of the NF-κB is a molecular hallmark of activated B cell-like diffuse large B cell lymphoma (ABC-DLBCL), and MALT1 may have utility as a treatment option for ABC-DLBCL. Previously, we described the discovery of novel MALT1 inhibitors with anti-proliferative effects in non-Hodgkin B-cell lymphoma cells and the strong anti-tumor activity of our MALT1 inhibitors across multiple tumor models as well as combination potential with agents including standard-of-care (ref 1, 2). SGR-1505 is an oral potent small molecule allosteric inhibitor of MALT1 that inhibits MALT1 enzymatic activity and demonstrates anti-proliferative activity in ABC-DLBCL cell lines, both BTKi-sensitive (OCI-LY10) and BTKi-resistant (OCI-LY3). When administered as a single agent and in combination with the approved Bruton's tyrosine kinase (BTK) inhibitor, ibrutinib, SGR-1505 demonstrated tumorostatic and regressive antitumor activity in ABC-DLBCL cell line-derived xenograft and patient-derived xenograft models. These data suggest that SGR-1505-mediated MALT1 inhibition has therapeutic potential for patients with selected B-cell lymphomas. Here we further characterized SGR-1505, in a series of in vitro and ex vivo assays, as well as RNA-seq analysis to examine changes in gene expression from in vivo tumor samples. We also compared SGR-1505 with a competitor Phase I candidate, JNJ-67856633 (JNJ-6633) (ref 3, 4). Results: SGR1505 potency and downstream effects were evaluated in a series of biochemical and cell based assays. SGR-1505 showed excellent potency in the biochemical assay and strong anti-proliferative effects on ABC-DLBCL cells. SGR-1505 was more potent than JNJ-6633 in all assays tested (Table 1). These results are also consistent with the result from a human primary T-cell based assay, where SGR-1505 showed at least ten-fold better potency than JNJ-6633. RNA-seq analysis was conducted to examine changes in gene expression from in vivo tumor samples. Greater modulation of BIOCARTA NF-kB pathway genes was seen with SGR-1505 compared to JNJ-6633, as measured by mean absolute change in gene expression. At 6 hr and later timepoints, we also observed a trend of increases in genes related to cell cycle pathways, such as cell cycle, DNA damage, and apoptosis. SGR-1505 is being evaluated in the SGR-1505-102 phase 1 study, which is an ongoing first-in-human, single center, dose escalation study to evaluate the safety, tolerability, PK and PD of SGR-1505 tablets in healthy participants (ACTRN12623000358640p). Preliminary data showed changes in target engagement markers at concentrations predicted by the in vitro and ex vivo assays, consistent with MALT1 protease inhibition. Conclusions: SGR-1505, a MALT1 protease small molecule inhibitor, consistently demonstrated better potency in in vitro and ex vivo assays when compared to the clinical-stage JNJ-6633 compound and greater effects on NF-kB pathway gene expression in in vivo tumor samples based on RNA-seq analysis. Changes in biological pathways mediated by MALT1 were also observed at relevant doses in the ongoing SGR-1505 healthy volunteer study. Currently, a phase 1 clinical trial in patients with mature B cell neoplasms is also ongoing (NCT05544019). The data presented suggests SGR-1505 has a potential best-in-class profile and supports advancing the ongoing clinical development of SGR-1505.

A Phase 1, Open-Label, Multicenter, Dose-Escalation Study of Sgr-1505 As Monotherapy in Subjects with Mature B-Cell Malignancies

Background and Significance: MALT1 (Mucosa-associated lymphoid tissue lymphoma translocation protein 1) is a component of the MALT1-BCL10-CARD11 complex downstream from the Bruton Tyrosine Kinase (BTK) on the B-cell receptor signaling pathway. MALT1 is a key mediator of nuclear factor kappa B (NF-κB) signaling, which is the main driver of a subset of B-cell lymphomas. MALT1 is considered a potential therapeutic target for several subtypes of non-Hodgkin B-cell lymphomas and chronic lymphocytic leukemia (CLL), including tumors with acquired BTK inhibitor (BTKi) resistance. Constitutive activation of NF-κB is a molecular hallmark of activated B cell-like diffuse large B cell lymphoma (ABC-DLBCL), and MALT1 may have utility as a treatment option for ABC-DLBCL. Furthermore, a MALT1 inhibitor (JNJ-67856633) showed efficacy in mature B cell malignancies from phase 1 studies (ref 1, 2). SGR-1505 is an oral potent small molecule allosteric inhibitor of MALT1 that inhibits MALT1 enzymatic activity and demonstrates anti-proliferative activity in BTKi-sensitive (OCI-LY10) and BTKi-resistant (OCI-LY3) ABC-DLBCL cell lines. SGR-1505 administered as a single agent and in combination with the approved Bruton's tyrosine kinase (BTK) inhibitor, ibrutinib, demonstrates tumorostatic and regressive antitumor activity in ABC-DLBCL cell line-derived and patient-derived xenograft models. These data suggest that SGR-1505-mediated MALT1 inhibition may expand therapeutic options for patients with selected B-cell lymphomas, supporting further evaluation of SGR-1505 in clinical trials. Study Design and Methods: SGR-1505-101 (NCT05544019) is a phase 1, multicenter trial of SGR-1505 as monotherapy in subjects with mature B-cell malignancies (figure 1). At present, the study is open to accrual at multiple investigative sites in the US with plans to expand to Europe. The primary objective is to evaluate safety and tolerability of SGR-1505 as monotherapy and to identify the maximum tolerated dose (MTD) and/or recommended dose (RD). Secondary objectives are to evaluate the pharmacokinetic (PK) profile, food effect, drug-drug interaction, and preliminary anti-tumor activity of SGR-1505. Key inclusion criteria are: history of mature B-cell malignancy (including aggressive and indolent B-cell lymphomas, Waldenström macroglobulinemia, and CLL); measurable or detectable disease according to the applicable disease-specific classification system (Lugano, iwCLL, WWM6); Eastern Cooperative Oncology Group (ECOG) performance status of ≤ 2. Patients with indolent B-cell lymphomas or CLL must have an indication for treatment and not require immediate cytoreductive therapy. Subjects with symptomatic or active CNS involvement, and other conditions or laboratory findings placing them at increased risk to the use of an investigational drug are excluded. SGR-1505 is initially dose-escalated using an accelerated titration design in cohorts of 1-6 subjects, and at higher dose levels using a conventional 3+3 design.

Crosstalk between autophagy and metabolic regulation of (CAR) T cells: therapeutic implications.

Despite chimeric antigen receptor (CAR) T cell therapy's extraordinary success in subsets of B-cell lymphoma and leukemia, various barriers restrict its application in solid tumors. This has prompted investigating new approaches for producing CAR T cells with superior therapeutic potential. Emerging insights into the barriers to CAR T cell clinical success indicate that autophagy shapes the immune response via reprogramming cellular metabolism and vice versa. Autophagy, a self-cannibalization process that includes destroying and recycling intracellular components in the lysosome, influences T cell biology, including development, survival, memory formation, and cellular metabolism. In this review, we will emphasize the critical role of autophagy in regulating and rewiring metabolic circuits in CAR T cells, as well as how the metabolic status of CAR T cells and the tumor microenvironment (TME) alter autophagy regulation in CAR T cells to restore functional competence in CAR Ts traversing solid TMEs.

SGR‐1505‐101: A PHASE 1, OPEN‐LABEL, MULTICENTER, DOSE‐ESCALATION STUDY OF SGR‐1505 AS MONOTHERAPY IN SUBJECTS WITH MATURE B‐CELL MALIGNANCIES

Background: MALT1 (Mucosa-associated lymphoid tissue lymphoma translocation protein 1) is a component of the MALT1-BCL10-CARD11 complex downstream from the Bruton Tyrosine Kinase (BTK) on the B-cell receptor signaling pathway. MALT1 is a key mediator of the nuclear factor kappa B (NF-κB) signaling, which is the main driver of a subset of B-cell lymphomas. MALT1 is considered a potential therapeutic target for several subtypes of non-Hodgkin B-cell lymphomas and chronic lymphocytic leukemia (CLL), including tumors with acquired BTK inhibitor (BTKi) resistance. In particular, constitutive activation of the NF-κB is a molecular hallmark of activated B cell-like diffuse large B cell lymphoma (ABC-DLBCL), and MALT1 may have utility as a treatment option for ABC-DLBCL. SGR-1505 is an oral potent small molecule allosteric inhibitor of MALT1 that inhibits MALT1 enzymatic activity, and demonstrates anti-proliferative activity in ABC-DLBCL cell lines, both BTKi-sensitive (OCI-LY10) and BTKi-resistant (OCI-LY3). SGR-1505 administered as a single agent and in combination with the approved Bruton's tyrosine kinase (BTK) inhibitor, ibrutinib, demonstrates tumorostatic and regressive antitumor activity in ABC-DLBCL cell line-derived xenograft and patient-derived xenograft models. Aims: These data suggest that SGR-1505-mediated MALT1 inhibition has therapeutic potential and may expand therapeutic options for patients with selected B-cell lymphomas supporting further evaluation of SGR-1505 in clinical trials. Methods: SGR-1505-101 (NCT05544019) is a phase 1, multicenter trial of SGR-1505 as monotherapy in subjects with mature B-cell malignancies. At present, the study has been activated in 3 sites in the United States. The primary objective is to evaluate safety and tolerability of SGR-1505 as monotherapy and to identify the maximum tolerated dose (MTD) and/or recommended dose (RD). Secondary objectives are to evaluate the pharmacokinetic (PK) profile, food effect, drug-drug interaction, and preliminary anti-tumor activity of SGR-1505. Key inclusion criteria are: history of mature B-cell malignancy (including aggressive and indolent B-cell lymphomas, Waldenström macroglobulinemia, and CLL); measurable or detectable disease according to the applicable disease-specific classification system (Lugano, iwCLL, WWM6); Eastern Cooperative Oncology Group (ECOG) performance status of ≤2. Patients with indolent B-cell lymphomas or CLL must have an indication for treatment and not require immediate cytoreductive therapy. Subjects with symptomatic or active CNS involvement, and other conditions or laboratory findings placing them at increased risk to the use of an investigational drug are excluded. SGR-1505 is initially dose-escalated using an accelerated titration design in cohorts of 1–6 subjects, and at higher dose levels using a conventional 3+3 design. Encore Abstract—previously submitted to EHA 2023 The research was funded by: Schrodinger Keywords: aggressive B-cell non-Hodgkin lymphoma, molecular targeted therapies, ongoing trials Conflicts of interests pertinent to the abstract. B. Yoo Employment or leadership position: Schrodinger Stock ownership: Schrodinger Z. Nie Employment or leadership position: Schrodinger Stock ownership: Schrodinger G. Krilov Employment or leadership position: Schrodinger Stock ownership: Schrodinger J. Tan Employment or leadership position: Schrodinger Stock ownership: Schrodinger H. Wright Employment or leadership position: Schrodinger Stock ownership: Schrodinger D. Weiss Employment or leadership position: Schrodinger Stock ownership: Schrodinger W. Yin Employment or leadership position: Schrodinger Stock ownership: Schrodinger K. Akinsanya Employment or leadership position: Schrodinger Stock ownership: Schrodinger

Targeting CD47 enhanced the antitumor immunity of PD-L1 blockade in B-cell lymphoma.

Background: Only a subset of B-cell lymphoma (BCL) patients can benefit from immune checkpoint inhibitors targeting PD-1/PD-L1. Materials & methods: In the A20 model, SIRPα-Fc and anti-PD-L1 were employed to target CD47 and PD-L1 simultaneously. Flow cytometry, immunofluorescence and quantitative polymerase chain reactionwere used to unravel the potential mechanisms. Results: Simultaneously targeting CD47 and PD-L1 activated CD8+ T cells with an increased release of effector molecules. Furthermore, infiltration of F4/80+iNOS+ M1 macrophages was enhanced by the dual therapy. Conclusion: Anti-CD47 therapy could sensitize BCL tumors to anti-PD-L1 therapy in a CD8+ T-cell- and M1-macrophage-dependent manner bypromoting cytotoxic lymphocyte infiltration, which mayprovide a potential strategy for BCL treatment by simultaneously targeting CD47 and PD-L1.

Small-molecule SUMO inhibition for biomarker-informed B-cell lymphoma therapy.

Aberrant activity of the SUMOylation pathway has been associated with MYC overexpression and poor prognosis in aggressive B-cell lymphoma (BCL) and other malignancies. Recently developed small-molecule inhibitors of SUMOylation (SUMOi) target the heterodimeric E1 SUMO activation complex (SAE1/UBA2). Here, we report that activated MYC signaling is an actionable molecular vulnerability in vitro and in a preclinical murine in vivo model of MYC-driven BCL. While SUMOi conferred direct effects on MYC-driven lymphoma cells, SUMO inhibition also resulted in substantial remodeling of various subsets of the innate and specific immunity in vivo. Specifically, SUMOi increased the number of memory B cells as well as cytotoxic and memory T cells, subsets that are attributed a key role within a coordinated anti-tumor immune response. In summary, our data constitute pharmacologic SUMOi as a powerful therapy in a subset of BCL causing massive remodeling of the normal B-cell and T-cell compartment.

Clinicopathologic Characteristics and A20 Mutation in Primary Thyroid Lymphoma.

Primary thyroid lymphoma (PTL) is a rare disease frequently arising against a background of autoimmune thyroiditis. It has recently been reported that the inactivation of the NF-κB negative regulator A20 by deletion and/or mutation could be involved in the pathogenesis of subsets of B-cell lymphomas. This study investigated the clinicopathologic characteristics and A20 mutation in patients with PTL. We analyzed the characteristics of 45 PTL patients (14 men and 31 women), with a median age of 71 (range, 35-90) years. A20 mutations were analyzed in DNA extracted from 20 samples consisting of 19 tumor tissue samples and 1 sample from Hashimoto's thyroiditis. Thirty-five patients (82%) had a history of Hashimoto's thyroiditis, and 29 (64%) had diffuse large B-cell lymphoma (DLBCL) and presented with larger tumors including bulky mass, elevated soluble interleukin-2 receptor levels, and a longer history of Hashimoto's thyroiditis than that of patients with mucosa-associated lymphoid tissue (MALT) lymphoma (n=16). A20 mutations were identified in 3 of 19 PTL patients (16%), in 2 of the 10 (20%) with DLBCL and in 1 of the 9 (11%) with MALT lymphoma. Interestingly, all patients with A20 mutations had Hashimoto's thyroiditis. Furthermore, they had a common missense variant in exon 3 (rs2230926 380T>G; F127C), which reduces the ability of A20 to inhibit NF-κB signaling. Our study suggests that the histological features of PTL affect clinical outcomes and that A20 mutations are related to PTL pathogenesis in some patients with Hashimoto's thyroiditis.

Validity of mutations as a cancer chronometer.

e15015 Background: Staging is devised to assess prognosis, and ultimately direct the management of cancer. Though staging systems don't necessarily confirm chronological progression from stage I to IV, there is near consensus that advanced stages are 'later' versions of a given cancer. This is reflected in the philosophy and efforts to identify 'early' cancer in screening programs. Tumor Mutational Burden (TMB) is one measure of the degree of proliferation, thus can be utilized as a molecular clock (Vogelstein), a surrogate for chronology. Since TMB is currently a clinical metric provided to oncologists in routine practice, proper interpretation of TMB is critical. We hypothesized that (i) metastatic disease is a ‘different’, rather than 'later' manifestation of a given cancer. Furthermore, we hypothesized that (ii) proliferation rates would be mirrored by the TMB, and lastly, that (iii) TMB will correlate with clinical virulence. Methods: (i) We mined the publicly-available TCGA database (cbioportal.org) for TMB from 558 samples spanning 5 whole genome & whole exome neoplasm datasets (Breast, Colon, Renal cell, Pancreatic, Cervical cancers). (ii) We compared the TMB in Burkitt's lymphoma, a highly proliferative neoplasm, with follicular lymphoma, a classically quiescent malignancy. (iii) We compared the TMB in skin squamous cell carcinoma (SSCC), a cancer with negligible impact on survival, with Acute Myelogenous Leukemia (AML), a highly lethal malignancy despite aggressive therapy. Results: (i) The 95% Confidence Intervals (CI) surrounding the median TMB were overlapping without statistical significance across ALL stages within EVERY histology examined. (ii) To our surprise, the TMB 95% CI were overlapping between the 2 subsets of B-cell lymphoma examined. (iii) TMB was substantially higher in SSCC (median of ̃800) compared to a mere 8 in AML. Conclusions: Assuming validity of Vogelstein’s molecular clock model, mutational probing does not support the concept that a stage IV malignancy is a chronologically delayed manifestation of a given neoplasm. Rather, we suggest an alternative approach where aggressive/metastatic cancers are inherently 'different' with unique abilities rather than a ‘later’ edition of a monodirectional succession. We also posit that cells that live for years (follicular lymphoma) can accumulate comparable levels of TMB as Burkitt's because the limited life span in Burkitt's (days to weeks) precludes the accumulation of high TMB. Finally, the clinical outcome cannot be discerned from the degree or mutability— which is rationally a predictor of immune susceptibility. It's noteworthy that the observed levels of mutations in SSCC, reflective of the sun mutagenicity, is more than 3-fold of that reported for melanoma (̃274) but this fact is rarely presented in cancer genomic landscapes, and may explain the rarity of metastatic SSCC owing to the immune clearance of metastases unlike the skin surface devoid of such immune access.

Characterization of Potent Paracaspase MALT1 Inhibitors for Hematological Malignancies

Introduction: MALT1 (mucosa-associated lymphoid tissue lymphoma translocation protein 1) is a key mediator of the NF-κB signaling pathway, the main driver of a subset of B-cell lymphomas and functions by forming a complex with CARMA1 and BCL10 to mediate antigen receptor-induced lymphocyte activation. MALT1 is considered a potential therapeutic target for several subtypes of non-Hodgkin B-cell lymphomas and chronic lymphocytic leukemia (CLL). Previously, we described the discovery of novel and potent MALT1 inhibitors with anti-proliferative effects in non-Hodgkin B-cell lymphoma cells. Here, we highlight the strong anti-tumor activity of our MALT1 inhibitors across multiple tumor models and the combination potential with agents including standard-of-care.Results: Novel small molecule MALT1 inhibitors were identified using Schrodinger's proprietary physics-based free energy perturbation (FEP+) modeling technology. These molecules demonstrate strong MALT1 protein binding affinity, potent inhibition of MALT1 enzymatic activity and anti-proliferative activity in the activated B-cell (ABC) subtype of diffuse large B cell lymphoma (DLBCL) cell lines such as OCI-LY3 and OCI-LY10. In combination with approved agents, these inhibitors demonstrate strong combination potential with Bruton's tyrosine kinase (BTK) inhibitors such as ibrutinib in ABC-DLBCL cell lines. In ABC-DLBCL CDX models, our representative MALT1 inhibitor induces tumor regression as a single agent and complete tumor regression in combination with ibrutinib. Our representative MALT1 inhibitor, when tested in LY2298 PDX models, demonstrates similar results. In addition, our representative MALT1 inhibitor was explored in a CDX model derived from a Mantle cell lymphoma REC-1 cell line, and demonstrates strong anti-tumor activity of ~78% tumor growth inhibition (TGI) as a single agent.Conclusions: Schrodinger's novel, potent MALT1 protease small molecule inhibitors are efficacious in in vitro B-cell lymphoma cell proliferation assays and in in vivo B-cell lymphoma xenograft models. These data suggest that targeting MALT1 may expand therapeutic options for patients with selected B-cell lymphomas, such as ABC-DLBCL, with the possibility of expanding into other B-cell lymphomas such as MCL. Furthermore, these small molecule MALT1 inhibitors demonstrate potential in combination with BTKi to overcome drug-induced resistance in patients with relapsed/refractory B-cell lymphomas. Taken together, the data presented here strongly underscore the therapeutic potential of our MALT1 inhibitor and support further evaluation in clinical trials. DisclosuresWeiss: Schrodinger: Current Employment; ARTham Therapeutics: Membership on an entity's Board of Directors or advisory committees.

Genetically-Defined Diffuse Large B-Cell Lymphoma Subsets Arise By Distinct Pathogenetic Mechanisms and Predict Outcome

Diffuse large B-cell lymphoma (DLBCL) is a heterogeneous disease that largely arises from antigen-exposed B-cells that transit through the germinal center (GC). DLBCL is further classified into transcriptional subtypes - activated B-cell (ABC) and GC B-cell (GCB). ABC DLBCLs exhibit genetic alterations in NF-kB modifiers and proximal components of the B-cell receptor (BCR) pathway and perturbed terminal B-cell differentiation. GCB DLBCLs have reported alterations in chromatin-modifying enzymes, PI3K signaling and Gα-migration pathway components and frequent translocations of BCL2 .Despite the recognized molecular heterogeneity in DLBCL, previously published genomic analyses have largely focused on single types of alterations - mutations, copy number alterations (CNAs) or structural variants (SVs) - in smaller data sets with more limited clinical annotation. An unbiased comprehensive analysis of all three alteration types is needed to define discrete, clinically annotated subtypes of DLBCL.We performed whole exome sequencing (WES) of 304 newly diagnosed DLBCLs, using an expanded bait set that captures recurrent SVs; 85% of study patients were uniformly treated with R-CHOP and had long-term follow-up. Somatic alterations (mutations, CNAs and SVs) and their clonality were determined with analytical pipelines developed at the Broad Institute. Notably, half of our DLBCL cohort lacked patient-matched normal samples, prompting the successful development of new methods to analyze tumor-only WES data. Significantly mutated genes (SMGs) were identified with MutSig2CV andrecurrent CNAs were defined with GISTIC2.0 .With increased sample size and improved methodology, we identified 158 SMGs, CNAs and SVs; the 98 SMGs included ones previously unreported in DLBCL but described in other lymphoid malignancies or cancer. Additional insights into the putative biological function of newly identified alterations were obtained by overlaying the predicted protein changes onto their 3-dimensional protein structures.We analyzed the mutational signatures in these DLBCLs and found that the majority of exome mutations were caused by spontaneous deamination at CpGs, a clock-like genetic signature associated with aging; only a minority of mutations were attributed to activation-induced cytidine deaminase (AID), an enzyme required for physiologic immunoglobulin receptor editing and aberrant somatic hypermutation.IGH, BCL2, BCL6 and MYC were the most frequently rearranged genes (40%, 21%, 19% and 8%, respectively). There were 18 arm-level and 18 focal regions of copy gain and 2 arm-level and 32 focal regions of copy loss with frequencies ranging between 5-32%.SMGs were significantly more likely to reside within focal CNAs (p=1x10-44), suggesting that these driver genes were perturbed by multiple mechanisms. Individual DLBCLs had a median of 17 genetic drivers, highlighting the need for a more comprehensive analysis. Therefore, we applied an integrated clustering approach to the recurrent mutations, CNAs and SVs and delineated 5 genetically distinct DLBCL subtypes and determined the likely temporal order of alterations within each cluster.This unbiased approach identified a previously unappreciated favorable risk ABC subset with genetic features of an extrafollicular, possibly marginal zone origin; a more tightly defined poor risk group of ABC DLBCLs with frequent BCL2 gain and concordant MYD88L265P / CD79B mutations; a distinct poor risk subset of GCB tumors with BCL2 SVs and alterations of PTEN and epigenetic enzymes and a discrete group of good risk GCB DLBCLs with specific alterations in BCR/PI3K, JAK/STAT and BRAF pathway components and multiple histones; and a Cell-of-Origin-independent subset with biallelic inactivation of TP53, 9p21.3/CDKN2A and associated genomic instability. These findings likely explain the variability in outcome predictions with the binary ABC- vs. GCB-DLBCL transcriptional classification and the challenges of therapeutically targeting less well defined DLBCLs.The genetically distinct DLBCL subsets provide a framework for assessing previously unrecognized heterogeneity in this disease, characterizing combinations of genetic alterations that drive DLBCL biology and guiding the development of rational single-agent and combination therapies in patients with the greatest need. DisclosuresCerhan:Janssen: Other: Scientific Advisory Board (REMICADELYM4001); Janssen: Other: Multiple Myeloma Registry Steering. Rodig:Bristol-Myers Squibb: Honoraria, Research Funding. Neuberg:Synta Pharmaceuticals: Other: Stock shares. Shipp:Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Research Funding; Gilead: Other: Scientific Advisory Board; Cell Signaling: Honoraria; Bayer: Research Funding; Takeda: Other: Scientific Advisory Board; Merck: Other: Scientific Advisory Board; AstraZeneca: Honoraria.

The Role of Mitochondrial Fat Oxidation in Cancer Cell Proliferation and Survival.

Tumors remodel their metabolism to support anabolic processes needed for replication, as well as to survive nutrient scarcity and oxidative stress imposed by their changing environment. In most healthy tissues, the shift from anabolism to catabolism results in decreased glycolysis and elevated fatty acid oxidation (FAO). This change in the nutrient selected for oxidation is regulated by the glucose-fatty acid cycle, also known as the Randle cycle. Briefly, this cycle consists of a decrease in glycolysis caused by increased mitochondrial FAO in muscle as a result of elevated extracellular fatty acid availability. Closing the cycle, increased glycolysis in response to elevated extracellular glucose availability causes a decrease in mitochondrial FAO. This competition between glycolysis and FAO and its relationship with anabolism and catabolism is conserved in some cancers. Accordingly, decreasing glycolysis to lactate, even by diverting pyruvate to mitochondria, can stop proliferation. Moreover, colorectal cancer cells can effectively shift to FAO to survive both glucose restriction and increases in oxidative stress at the expense of decreasing anabolism. However, a subset of B-cell lymphomas and other cancers require a concurrent increase in mitochondrial FAO and glycolysis to support anabolism and proliferation, thus escaping the competing nature of the Randle cycle. How mitochondria are remodeled in these FAO-dependent lymphomas to preferably oxidize fat, while concurrently sustaining high glycolysis and increasing de novo fatty acid synthesis is unclear. Here, we review studies focusing on the role of mitochondrial FAO and mitochondrial-driven lipid synthesis in cancer proliferation and survival, specifically in colorectal cancer and lymphomas. We conclude that a specific metabolic liability of these FAO-dependent cancers could be a unique remodeling of mitochondrial function that licenses elevated FAO concurrent to high glycolysis and fatty acid synthesis. In addition, blocking this mitochondrial remodeling could selectively stop growth of tumors that shifted to mitochondrial FAO to survive oxidative stress and nutrient scarcity.

Identification of Potent Paracaspase MALT1 Inhibitors for Hematological Malignancies

Introduction: MALT1 (mucosa-associated lymphoid tissue lymphoma translocation protein 1), was identified as a translocation protein fused with cIAP2 in mucosa-associated lymphoid tissue (MALT) B cell lymphomas. MALT1, a key mediator of NF-κB signaling and the main driver of a subset of B-cell lymphomas, functions via formation of a complex with CARMA1 and BCL10 to mediate antigen receptor-induced lymphocyte activation. MALT1 has been considered as a potential therapeutic target for several non-Hodgkin B cell lymphomas as well as chronic lymphocytic leukemia (CLL). Here, we describe the discovery of novel, potent MALT1 inhibitors that result in antiproliferative effects in non-Hodgkin B-cell lymphoma cells. Results: We have identified novel small molecule MALT1 inhibitors using our proprietary physics-based Free Energy Perturbation (FEP+) modeling technology. Our compounds show potent (sub nM) inhibition of MALT1 enzymatic activity, as well as high binding affinity (sub nM) to MALT1 protein measured by Surface Plasmon Resonance (SPR). BCL10 is a binding partner of MALT1 that is cleaved by MALT1 at the C-terminus. Our inhibitors were efficacious in a target engagement assay showing prevention of BCL10 cleavage in Activated B-cell (ABC) subtype of diffuse large B cell lymphoma (DLBCL) cell lines OCI-LY3 and OCI-LY10, which are Bruton tyrosine kinase (BTK) inhibitor ibrutinib-resistant and -responsive respectively. Our compounds are potent inhibitors of IL10 secretion in both OCI-LY3 and OCI-LY10 cells, which is consistent with the inhibition of NF-κB signaling. We also examined the effect of our MALT1 inhibitors on ABC-DLBCL cell proliferation. Our inhibitors demonstrated potent anti-proliferative effects in both OCI-LY3 and OCI-LY10 cell lines, as well as synergistic effects with ibrutinib in a BTKi sensitive ABC-DLBCL cell panel. Examinations of a protease panel and off-target safety screening panel, as well as in vivo high dose tolerability study showed our compound had excellent selectivity and significant safety margin. Plasma IL10 and tumor BCL10 have been identified as robust PD markers in PK/PD studies in both OCI-LY3 and OCI-LY10 tumor bearing mice. Dose-dependent tumor growth inhibition was observed after 3 weeks of treatment in OCI-LY3 xenograft model, with efficacy also observed in combination with venetoclax. Ongoing work: We are continuing to explore the synergistic effects of our compounds with BTK inhibitors in B-cell lymphoma mouse models. Preliminary data showed potent inhibition of IL-2 secretion in Jurkat cells from our compound treatment. Additional studies are ongoing to elucidate the role of MALT1 inhibition in Treg as well as Teffector cells in vitro and in vivo. Refinement of the current inhibitor series, using co-crystal structures, is in progress in preparation for further development of optimized molecules. Conclusion and Future Plans: We have identified novel potent MALT1 protease small molecule inhibitors that are efficacious in the in vitro B-cell lymphoma cell proliferation assays and in the in vivo B-cell lymphoma xenograft model. Our data suggest that targeting MALT1 may expand therapy options for patients with selected B-cell lymphomas, such as ABC-DLBCL. Our work provided insight into the anti-tumor efficacy of our inhibitors in B-cell lymphomas as single agent, and ongoing work will continue to assess the potential combination with BTKi to overcome drug-induced resistance in patients with relapsed/refractory B-cell lymphoma. Disclosures Yin: Schrodinger: Current Employment, Current equity holder in publicly-traded company. Zhe:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Placzek:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Trzoss:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Krilov:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Feng:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Lawrenz:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Pelletier:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Lai:Triplet Therapeutics: Current Employment, Current equity holder in private company. Bell:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Calkins:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Grimes:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Tang:Schrodinger: Current Employment, Current equity holder in publicly-traded company. McRobb:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Gerasyuto:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Feher:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Mondal:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Jensen:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Wright:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Akinsanya:Schrodinger: Current Employment, Current equity holder in publicly-traded company.

Abstract PO-45: Robust detection of translocations in lymphoma FFPE samples using Targeted Locus Capture-based sequencing

Abstract Chromosomal translocations with immunoglobin (IG) loci are the classic drivers in a large subset of B-cell lymphomas. Detection of these translocations is important for confirmation of diagnosis and for prognosis and therapy decisions. Currently, molecular diagnosis of translocations in lymphomas is not addressed well by next-generation sequencing (NGS). The standard method for detection of translocations is fluorescence in situ hybridization (FISH), which is labor intensive and can be difficult to interpret. There is a need for a robust technology that can be standardized. Targeted Locus Capture (TLC) selectively enriches and sequences entire genes based on the crosslinking of physically proximal sequences, and thereby enables complete sequencing of genes of interest, including detection of large structural variants. Because the technology is based on the crosslinking and fragmenting of DNA, it has particular advantages in the analysis of formalin-fixed, paraffin-embedded (FFPE) samples in which DNA is inherently crosslinked and fragmented. In order to validate the FFPE-TLC technology as a novel approach for translocation detection in lymphoma samples, we have developed a panel assay containing genes with frequent translocations (MYC, BCL2, BCL6, IG loci). With this assay we have analyzed >140 lymphoma and control FFPE samples of variable input amounts and qualities that had previously been analyzed with FISH, and a subset also with standard targeted NGS. Good concordance with FISH results was observed for both translocation-positive and -negative samples. In 10 cases for which FFPE-TLC analysis resulted in a different finding than FISH, discordance could be explained by higher sensitivity of FFPE-TLC or by inconclusive FISH results. In a specific case, FFPE-TLC detected a small-distance rearrangement on chromosome 3 that caused a BCL6 fusion but led to insufficient and therefore undetectable break-apart with FISH. Secondly, the FFPE-TLC approach was tested on a set of 19 B-cell lymphoma FFPE samples that had previously been analyzed using standard targeted NGS and FISH and was enriched for discordant results between these methods. FFPE-TLC-based NGS enables more robust translocation calling as the detection relies on broad sequencing coverage across the translocation partner rather than on breakpoint sequences only. In 3 cases, FFPE-TLC could proof false negative calls in standard targeted NGS due to breakpoints located in regions difficult to capture or to sequence. In 1 case, standard targeted NGS had made a false positive call on a breakpoint sequence that was shown to be caused by a small insertion rather than a genuine translocation. This study shows that FFPE-TLC promises to be a robust alternative for FISH analysis and standard targeted NGS procedures in lymphoma diagnostics and in other cancers with frequent structural variants. The FFPE-TLC approach enables a single, DNA-based NGS test detecting both small mutations and translocations. Citation Format: Amin Allahyar, Mark Pieterse, Joost Swennenhuis, Tjitske Los-de Vries, Mehmet Yilmaz, Roos Leguit, Ruud Meijers, Nathalie Hijmering, Daphne de Jong, Bauke Ylstra, Robert van der Geize, Joost Vermaat, Arjen Cleven, Tom van Wezel, Arjan Diepstra, Leon van Kempen, Karima Hajo, Harma Feitsma, Marieke Simonis, Max van Min, Erik Splinter, Wouter de Laat. Robust detection of translocations in lymphoma FFPE samples using Targeted Locus Capture-based sequencing [abstract]. In: Proceedings of the AACR Virtual Meeting: Advances in Malignant Lymphoma; 2020 Aug 17-19. Philadelphia (PA): AACR; Blood Cancer Discov 2020;1(3_Suppl):Abstract nr PO-45.

WHERE ARE THE EFFUSIONS?

SESSION TITLE: Fellows Pulmonary Manifestations of Systemic Disease Posters SESSION TYPE: Fellow Case Report Posters PRESENTED ON: October 18-21, 2020 INTRODUCTION: Primary effusion lymphoma (PEL) is a rare and aggressive subset of B-cell lymphoma that is commonly associated with immune deficiencies such as HIV/AIDS and organ transplant. It commonly manifests as a serous effusion in either pleural, pericardial or peritoneal spaces, and is associated with human herpesvirus-8 (HHV-8) or Epstein-Barr virus (EBV). One study showed that about one third of patients with the diagnosis of PEL did not have effusions; but were diagnosed by pathology of solid tumors. CASE PRESENTATION: A 58-year-old man with a multi-decade history of HIV infection was referred to the Emergency Department for anemia and low CD4 T cell count with elevated HIV viral load. He had a long history of HIV infection. Other medical problems include Kaposi sarcoma, hypertension, and spinal osteoarthritis. His physical exam was notable for pre-auricular and inguinal lymphadenopathy. Initial laboratory evaluation included anemia, leukocytosis with left shift, thrombocytopenia, elevated serum protein, low bicarbonate and elevated lactate. He was given fluid resuscitation, broad-spectrum antibiotics, and vasopressor support. Cerebrospinal fluid studies showed high total protein at 72, 88% lymphocytes. Continued evaluation of his lymphadenopathy, anemia and thrombocytopenia included detection of EBV and HHV-8. Excisional biopsy of left cervical lymph node showed clusters and sheets of large atypical cells with plasmablastic morphology admixed with small mature lymphocytes and plasma cells. The suspected diagnosis was primary effusion lymphoma without lymphomatous effusions. His course was complicated by respiratory insufficiency requiring non invasive ventilation in the setting of new bilateral ground glass opacities. He was treated for pneumonia with clinical improvement. He became altered on the medical floor, and a guardian was appointed for his medical decision making. In light of HIV-associated lymphoma with unclear benefit to aggressive chemotherapy, his guardian opted for comfort care and he was discharged to home hospice. DISCUSSION: We present a case of PEL presenting in a patient with long-standing HIV infection and history of Kaposi sarcoma. Despite the name, not all cases have lymphomatous effusions on presentation. PEL is uncommon, and available information is based on case series. The treatment of PEL involves multi-drug chemotherapy, including use of CHOP (cyclophosphamide, doxorubicin, vincristine and prednisolone) and methotrexate. One case series of 28 patients treated for PEL with CHOP had median overall survival of 6.2 months . Another case series of 51 patients treated for PEL using CHOP-like regimen and the addition of methotrexate showed median overall survival 10.2 months . CONCLUSIONS: The prevalence of PEL is low; but should be considered in in patients with long standing HIV infection and Kaposi sarcoma. Reference #1: Guillet, S., Gérard, L., Meignin, V., Agbalika, F., Cuccini, W., Denis, B., Katlama, C., Galicier, L. and Oksenhendler, E. (2016), Classic and extracavitary primary effusion lymphoma in 51 HIV-infected patients from a single institution. Am. J. Hematol., 91: 233-237. doi:10.1002/ajh.24251 Reference #2: Kazuyuki Shimada, Fumihiko Hayakawa, Hitoshi Kiyoi; Biology and management of primary effusion lymphoma. Blood 2018; 132 (18): 1879–1888. doi: https://doi.org/10.1182/blood-2018-03-791426 Reference #3: Emmanuelle Boulanger, Laurence Gérard, Jean Gabarre, Jean-Michel Molina, Christophe Rapp, Jean-François Abino, Jacques Cadranel, Sylvie Chevret, and Eric Oksenhendler Prognostic Factors and Outcome of Human Herpesvirus 8–Associated Primary Effusion Lymphoma in Patients With AIDS (2005) Journal of Clinical Oncology 23:19, 4372-4380 DISCLOSURES: No relevant relationships by Saud Alrawaf, source=Web Response No relevant relationships by Benjamin DelPrete, source=Web Response No relevant relationships by Lisa Glass, source=Web Response No relevant relationships by Marwa Oudah, source=Web Response

BCL-W is dispensable for the sustained survival of select Burkitt lymphoma and diffuse large B-cell lymphoma cell lines

AbstractDysregulated expression of BCL-2 family proteins allows cancer cells to escape apoptosis. To counter this, BH3-mimetic drugs that target and inhibit select BCL-2 prosurvival proteins to induce apoptosis have been developed for cancer therapy. Venetoclax, which targets BCL-2, has been effective as therapy for patients with chronic lymphocytic leukemia, and MCL-1–targeting BH3-mimetic drugs have been extensively evaluated in preclinical studies for a range of blood cancers. Recently, BCL-W, a relatively understudied prosurvival member of the BCL-2 protein family, has been reported to be abnormally upregulated in Burkitt lymphoma (BL), diffuse large B-cell lymphoma (DLBCL), and Hodgkin lymphoma patient samples. Therefore, to determine if BCL-W would be a promising therapeutic target for B-cell lymphomas, we have examined the role of BCL-W in the sustained growth of human BL- and DLBCL-derived cell lines. We found that CRISPR/CAS9-mediated loss or short hairpin RNA-mediated knockdown of BCL-W expression in selected BL and DLBCL cell lines did not lead to spontaneous apoptosis and had no effect on their sensitivity to a range of BH3-mimetic drugs targeting other BCL-2 prosurvival proteins. Our results suggest that BCL-W is not universally required for the sustained growth and survival of human BL and DLBCL cell lines. Thus, targeting BCL-W in this subset of B-cell lymphomas may not be of broad therapeutic benefit.

Hitting back at lymphoma: How do modern diagnostics identify high-risk diffuse large B-cell lymphoma subsets and alter treatment?

Diffuse large B-cell lymphoma (DLBCL) is a clinically and biologically heterogeneous disease. Diagnostic tools in the clinic can now identify distinct subsets characterized by unique molecular features, which are increasingly transforming how these patients are managed. Activated B-cell-like DLBCL is characterized by NF-κB activation and chronic B-cell receptor signaling and may be targeted with lenalidomide or ibrutinib in the relapsed setting. Germinal center-like DLBCL is enriched for activating EZH2 mutations, and encouraging activity has been observed for the EZH2 inhibitor tazemetostat, which now has a fast-track US Food and Drug Administration designation. Double-hit lymphoma is a high-grade B-cell lymphoma characterized by translocations of MYC and BCL2 and/or BCL6 and carries a poor prognosis. Intensive chemoimmunotherapy strategies appear to be superior to standard R-CHOP (rituximab combined with cyclophosphamide, doxorubicin, vincristine, and prednisone) as initial therapy, and anti-CD19 chimeric antigen receptor T cells are inducing remission in patients with relapsed/refractory disease who previously had few available options. Primary mediastinal (thymic) large B-cell lymphoma is a molecularly distinct large-cell lymphoma with clinical and molecular features that overlap with those of classical Hodgkin lymphoma. R-CHOP has been associated with an unacceptably high rate of primary treatment failure in this young population, whereas dose-adjusted EPOCH-R (etoposide, prednisone, vincristine, cyclophosphamide, and doxorubicin plus rituximab) produces durable remissions without the need for radiotherapy in most patients. For relapsed/refractory disease, immune checkpoint inhibitors targeting PD-1 have shown promising activity in chemotherapy-refractory disease, as have anti-CD19 chimeric antigen receptor T cells. Additional therapeutic targets, including JAK2, continue to be evaluated. The identification of discrete biological subsets is steadily moving us away from a "one-size-fits-all" approach in DLBCL.

Role of Serial Positron Emission Tomography (PET) Scans in Indolent Lymphomas' Management - Interim Results from an Ongoing Prospective Study at King Fahd Medical City, Riyadh, Saudi Arabia

Background:Indolent lymphomas (ind-LYM) are a subset of B-cell lymphomas, characterized by slow growth, protracted course without treatment and a tendency to reoccur after therapy. The management of ind-LYM is varied and evolving. To-date reliable tools for imaging based prognostication and treatment strategies are limited. We explored the utility of serial FDG PET scans (baseline (BL), interim/6 months (INT) end of therapy/1 year (EOT)), in managing ind-LYM).Methods:From an ongoing prospective study, examining the role of PET scan in ind-LYM at our institution, we performed an interim analysis of all patients hitherto enrolled in our study. Patients diagnosed as ind-LYM and having undergone serial PET scans from 2015 to date (N=40, males= 27, females =13) had median age of 59.68 ± 14.5 (28-82 at diagnosis. All PET scans were obtained per accepted protocols. SUVmax and Deauville scores (DS) were obtained from five target lesions. The average of composite SUV (cSUV) and composite Deauville scores (cDS) were computed for each patient. Statistical analyses (using t-test, mean delta change) were performed with the cSUV and cDS.Results:The types of ind-LYM were CLL/SLL (17), Follicular (15), mantle cell (3), marginal zone lymphoma (3), and 1 each of MALT and lymphoplasmacytic lymphoma. The data were analyzed for two arms of the study treatment chemotherapy arm (CHEMO-22/40) and Rituximab + observation arm (OBSR-18/40). At BL, patients on CHEMO had significantly higher cSUV and cDS compared to those who were on OBSR (SUV: 6.99 vs. 4.32 p-value 0.0124; cDS: 4.37 vs 3.71 p-value 0.0075 respectively). Although there was a delta change in the cSUV and cDS in both arms after INT and EOT, both treatment lines showed no significant difference in the SUV mean and DS (p-value: 0.754 and 0.5721, receptively). A 2-tailed T-test was used for delta change of cSUV. BL to INT cSUV was statistically significant (p-valve 0.05) and difference in cSUV was not significant for BL to EOT (p-valve 0.98). Difference in cDS was not significant between BL, INT and EOT.Conclusion:The higher cSUV/cDS at BL for the treatment arm may be due to disease profile at the time of presentation and/or selection bias. At EOT no difference in both estimates were noted. Both arms showed similar trends in delta change from BL-INT-EOT. Our findings suggest that SUV and DS at BL maybe an independent criterion for treatment selection in ind-LYM. DisclosuresNo relevant conflicts of interest to declare.

Cooperation between SYK and ZAP70 Kinases As a Driver of Oncogenic BCR-Signaling in B-Cell Malignancies

The spleen tyrosine kinase (SYK) and ζ-associated protein of 70 kD (ZAP70) tyrosine kinases play critical roles in proximal signal transduction of B-cell (BCR) and T-cell receptors (TCR), respectively. The highly similar SYK and ZAP70 kinases share a common structure composed of two tandem SH2 domains and a carboxy-terminal kinase domain. A linker region, termed interdomain B, connects the SH2 domains to the kinase domain and is important for kinase activation. Despite their conserved structure, SYK and ZAP70 are expressed in a largely mutually exclusive manner and play analogous roles in BCR- and TCR-signaling.Cross-lineage activation of ZAP70 in B cells was previously identified in chronic lymphocytic leukemia (CLL), which is characterized by clonal accumulation of malignant CD5+ B-cell cells that retain dependency on the BCR for survival signals. Nearly half of CLL cases show co-expression of SYK and ZAP70, and these patients have an aggressive disease course and a poor prognosis.Our analysis shows that in addition to CLL, aberrant ZAP70 expression occurs in other B-cell malignancies, e.g. TCF3-PBX1 pre-B ALL and B-cell lymphoma subsets that depend on survival signals from a functional (pre-) BCR. These findings suggest that interactions between SYK and ZAP70 may function to fine-tune strength of oncogenic BCR-signaling.To test this hypothesis, we have used a combination of molecular and proteomic approaches. We studied mechanisms by which ZAP70 integrates into BCR-mediated signals, and how the function of ZAP70 in B-cells differs from its native role downstream of the TCR. We demonstrate that ectopically expressed SYK and ZAP70 proteins are constitutively phosphorylated in BCR-ABL1+ B-ALL cells, but these induce distinctive signaling thresholds. CRISPR-mediated deletion of SYK or ZAP70 in leukemic cells further revealed that SYK and ZAP70 regulate unique signaling pathways in B-cells.We also demonstrate that ZAP70 is activated following BCR stimulation of lymphoma cells, and SYK/ZAP70 co-expressing cells display enhanced BCR signaling. Interestingly, enhanced BCR signaling was also observed in cells engineered to express an alternative splice variant of SYK (SYK-S). This shorter isoform of SYK, lacks a 23 amino-acid insert in the interdomain-B linker region, which is also absent in ZAP70, and may define unique protein-interactions that modulate signaling outcome. To elucidate the differential interactome of SYK, SYK-S, and ZAP70 we performed proximity-dependent biotin identification (BioID) experiments in B-cells following BCR-activation to capture the core signalling networks of these kinases in leukemic cells. In addition to expected BCR components including BLNK, PTPN6 and CBL we identified novel SYK and ZAP70 associated molecules including IKZF3, LAT2 and WAS which may play important roles in the survival of BCR-dependent malignancies. Importantly our findings highlight a role for ZAP70 in oncogenic BCR-signaling and suggest that ZAP70 promotes oncogenic BCR-signaling by limiting the ability of the BCR to induce negative B-cell selection and cell death. DisclosuresNo relevant conflicts of interest to declare.

Integration of Nanostring Profiling and Functional Characterization of Oxidative and Replicative Stress Biomarkers Identifies Poor Prognosis MYC/BCL-2 Positive Diffuse Large B-Cell Lymphoma Subsets, Providing Opportunities for Precision Therapies

Integration of Nanostring Profiling and Functional Characterization of Oxidative and Replicative Stress Biomarkers Identifies Poor Prognosis MYC/BCL-2 Positive Diffuse Large B-Cell Lymphoma Subsets, Providing Opportunities for Precision Therapies

Papillary thyroid carcinoma expressing CD20.

We identified a case of lymphadenopathy of metastatic papillary thyroid carcinoma (PTC) with CD20 expression, which was also expressed by the primary tumor. CD20 expression was identified using immunohistochemistry (IHC) in metastatic PTC biopsy samples from a 58-year-old woman. CD20 expression was initially determined using a CD20-recognizing L26 clone. To validate this phenomenon, we performed IHC with another antibody that recognizes the N-terminus of CD20 and fluorescent double staining using anti-TTF-1 and anti-CD20 antibodies. Taken together, we concluded metastatic PTC expressed CD20. We also examined 21 additional PTC cases and found four more cases that were CD20 positive. Therefore, five of the 22 (23%) cases were positive for CD20. In the positive cases, four cases were classical papillary thyroid carcinoma and one case was a follicular variant of papillary thyroid carcinoma. CD20 is an important target for molecularly targeted therapy for a subset of B-cell lymphomas. Complement-dependent and antibody-dependent cellular cytotoxicities are important effector mechanisms of anti-CD20 therapy. Here, for the first time, we report PTC with expression of CD20. Our findings provide a rationale for treating CD20-positive PTC patients with anti-CD20 therapy.