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Supplementary Data from MYC Levels Regulate Metastatic Heterogeneity in Pancreatic Adenocarcinoma

The degree of metastatic disease varies widely among patients with cancer and affects clinical outcomes. However, the biological and functional differences that drive the extent of metastasis are poorly understood. We analyzed primary tumors and paired metastases using a multifluorescent lineage-labeled mouse model of pancreatic ductal adenocarcinoma (PDAC)—a tumor type in which most patients present with metastases. Genomic and transcriptomic analysis revealed an association between metastatic burden and gene amplification or transcriptional upregulation of MYC and its downstream targets. Functional experiments showed that MYC promotes metastasis by recruiting tumor-associated macrophages, leading to greater bloodstream intravasation. Consistent with these findings, metastatic progression in human PDAC was associated with activation of MYC signaling pathways and enrichment for MYC amplifications specifically in metastatic patients. Collectively, these results implicate MYC activity as a major determinant of metastatic burden in advanced PDAC.Significance:Here, we investigate metastatic variation seen clinically in patients with PDAC and murine PDAC tumors and identify MYC as a major driver of this heterogeneity.This article is highlighted in the In This Issue feature, p. 275

Supplementary Figure from MYC Levels Regulate Metastatic Heterogeneity in Pancreatic Adenocarcinoma

The degree of metastatic disease varies widely among patients with cancer and affects clinical outcomes. However, the biological and functional differences that drive the extent of metastasis are poorly understood. We analyzed primary tumors and paired metastases using a multifluorescent lineage-labeled mouse model of pancreatic ductal adenocarcinoma (PDAC)—a tumor type in which most patients present with metastases. Genomic and transcriptomic analysis revealed an association between metastatic burden and gene amplification or transcriptional upregulation of MYC and its downstream targets. Functional experiments showed that MYC promotes metastasis by recruiting tumor-associated macrophages, leading to greater bloodstream intravasation. Consistent with these findings, metastatic progression in human PDAC was associated with activation of MYC signaling pathways and enrichment for MYC amplifications specifically in metastatic patients. Collectively, these results implicate MYC activity as a major determinant of metastatic burden in advanced PDAC. Significance: Here, we investigate metastatic variation seen clinically in patients with PDAC and murine PDAC tumors and identify MYC as a major driver of this heterogeneity. This article is highlighted in the In This Issue feature, p. 275

SummaryThe initiation and progression of cancer are inextricably linked to the tumor microenvironment (TME). Understanding the function of specific cancer-TME interactions poses a major challenge due in part to the complexity of the in vivo microenvironment. Here we predict cancer-TME interactions from single cell transcriptomic maps of both human colorectal cancers (CRCs) and mouse CRC models, ask how these interactions are altered in established, long-term human tumor organoid (tumoroid) cultures, and functionally recapitulate human myeloid-carcinoma interactions in vitro. Tumoroid cultures suppress gene expression programs involved in promoting inflammation and immune cell migration through receptor-ligand interactions, providing a reductive platform for re-establishing carcinoma-immune cell interactions in vitro. Introduction of human monocyte-derived macrophages into tumoroid cultures instructs macrophages to acquire pro-tumorigenic gene expression programs similar to those observed in vivo. This includes hallmark induction of SPP1, encoding Osteopontin, an extracellular CD44 ligand with established oncogenic effects. Taken together, these findings offer a framework for understanding CRC-TME interactions and provide a reductionist tool for modeling specific aspects of these interactions.

Summary Tumor-associated macrophages (TAMs) play an important role in tumor immunity and comprise of subsets that have distinct phenotype, function, and ontology. Transcriptomic analyses of human medulloblastoma, the most common malignant pediatric brain cancer, showed that medulloblastomas (MBs) with activated sonic hedgehog signaling (SHH-MB) have significantly more TAMs than other MB subtypes. Therefore, we examined MB-associated TAMs by single-cell RNA sequencing of autochthonous murine SHH-MB at steady state and under two distinct treatment modalities: molecular-targeted inhibitor and radiation. Our analyses reveal significant TAM heterogeneity, identify markers of ontologically distinct TAM subsets, and show the impact of brain microenvironment on the differentiation of tumor-infiltrating monocytes. TAM composition undergoes dramatic changes with treatment and differs significantly between molecular-targeted and radiation therapy. We identify an immunosuppressive monocyte-derived TAM subset that emerges with radiation therapy and demonstrate its role in regulating T cell and neutrophil infiltration in MB.

Epithelial plasticity, or epithelial-to-mesenchymal transition (EMT), is a well-recognized form of cellular plasticity, which endows tumor cells with invasive properties and alters their sensitivity to various agents, thus representing a major challenge to cancer therapy. It is increasingly accepted that carcinoma cells exist along a continuum of hybrid epithelial-mesenchymal (E-M) states and that cells exhibiting such partial EMT (P-EMT) states have greater metastatic competence than those characterized by either extreme (E or M). We described recently a P-EMT program operating in vivo by which carcinoma cells lose their epithelial state through post-translational programs. Here, we investigate the underlying mechanisms and report that prolonged calcium signaling induces a P-EMT characterized by the internalization of membrane-associated E-cadherin (ECAD) and other epithelial proteins as well as an increase in cellular migration and invasion. Signaling through Gαq-associated G-protein-coupled receptors (GPCRs) recapitulates these effects, which operate through the downstream activation of calmodulin-Camk2b signaling. These results implicate calcium signaling as a trigger for the acquisition of hybrid/partial epithelial-mesenchymal states in carcinoma cells.

Primary malignant bone tumors are rare, occur in all age groups, and include distinct entities such as osteosarcoma, Ewing sarcoma, and chondrosarcoma. Traditional treatment with some combination of chemotherapy, surgery, and radiation has reached the limit of efficacy, with substantial room for improvement in patient outcome. Furthermore, genomic characterization of these tumors reveals a paucity of actionable molecular targets. Against this backdrop, recent advances in cancer immunotherapy represent a silver lining in the treatment of primary bone cancer. Major strategies in cancer immunotherapy include stimulating naturally occurring anti-tumor T cells and adoptive transfer of tumor-specific cytotoxic T cells. Chimeric antigen receptor T cells (CAR-T cells) belong to the latter strategy and are an impressive application of both insights into T cell biology and advances in genetic engineering. In this review, we briefly describe the CAR-T approach and discuss its applications in primary bone tumors. © 2019 American Society for Bone and Mineral Research.

Malignant bowel obstruction (MBO) is a common problem for patients with advanced malignancy, especially colorectal and ovarian cancers. Symptoms include pain, bloating, nausea and vomiting, and inability to eat. Treatment options consist of a wide range of surgical and nonsurgical interventions (medications, endoscopic, or interventional radiology approaches). Outcomes are variable no matter the strategy, and the optimal approach is often not clear. Greater research is needed to assist decision-making for clinicians treating patients with MBO.

The degree of metastatic disease varies widely amongst cancer patients and impacts clinical outcomes. However, the biological and functional differences that drive the extent of metastasis are poorly understood. We analyzed primary tumors and paired metastases using a multi-fluorescent lineage-labeled mouse model of pancreatic ductal adenocarcinoma (PDAC) – a tumor type where most patients present with metastases. Genomic and transcriptomic analysis revealed an association between metastatic burden and gene amplification or transcriptional upregulation ofMYCand its downstream targets. Functional experiments showed that MYC promotes metastasis by recruiting tumor associated macrophages (TAMs), leading to greater bloodstream intravasation. Consistent with these findings, metastatic progression in human PDAC was associated with activation of MYC signaling pathways and enrichment for MYC amplifications specifically in metastatic patients. Collectively, these results implicate MYC activity as a major determinant of metastatic burden in advanced PDAC.

Soft tissue sarcomas (STS) comprise a heterogeneous group of solid tumors arising from mesodermal tissues. With few effective systemic therapies, advanced-stage STS is frequently fatal. Immune checkpoint blockade (ICB) is currently under investigation for the treatment of STS. However, STS harbor a highly immunosuppressive tumor microenvironment (TME) that inhibits effective antitumor T cell responses, with only a subset of patients responding to ICB. While the major focus of immunotherapy to date has been on the role of T cells, targeting innate immune cells such as tumor associated macrophages (TAMs) within the TME holds great promise. TAMs are the most abundant leukocytes in STS, and contribute to the establishment of an immunosuppressive TME through multiple mechanisms. We identified the endothelin B receptor (EDNRB) as a potential novel therapeutic target on TAMs based on an analysis of TCGA data. EDNRB is highly expressed in “immunologically quiet” tumors with high macrophage to T cell ratios and M2-like gene expression. EDNRB encodes a G-protein-coupled receptor that binds the vasoactive peptides endothelin (EDN) 1, 2, or 3. EDNRB is upregulated during macrophage differentiation, and is highly expressed by certain macrophages subsets, including TAMs. However, the role of the EDN-EDNRB axis in regulating macrophage function and antitumor immunity is unknown. Using a murine syngeneic transplant model with cell lines derived from methylcholanthrene-induced fibrosarcomas, we first genetically deleted or overexpressed the ligand Edn1 in sarcoma cells prior to transplant. Genetic deletion of Edn1 using CRISPR-Cas9 resulted in significantly increased major histocompatibility complex class II (MHCII) expression in TAMs, indicative of a more immunostimulatory phenotype. RNA-seq of sorted TAMs from Edn1 CRISPR tumors revealed enrichment for gene sets involved in antitumor immunity, including interferon gamma and NF-kB. Conversely, overexpression of Edn1 dramatically reduced TAM MHCII expression. Furthermore, knockout of Edn1 or pharmacologic blockade of EDNRB significantly enhanced responses to anti-PD1. To confirm these effects were mediated by macrophage EDNRB, we proceeded to generate a conditional deletion of Ednrb in TAMs by crossing Ednrbflox/flox and LysM-Cre mice. Consistent with our hypothesis, TAMs from sarcomas in LysM-Cre:Ednrbflox/flox mice also took on an immunostimulatory phenotype, with increased MHCII expression and reduced M2 markers. Taken together, these findings support the existence of a novel regulatory axis, whereby tumor-derived endothelins promote a suppressive TAM phenotype through macrophage EDNRB. Combining endothelin receptor antagonists with immune checkpoint blockade has the potential to enhance antitumor immune responses in STS and other solid tumors by targeting both innate and adaptive immune cells within the TME. Citation Format: Ian Wesley Folkert, Tsun Ki Jerrick To, Samir Devalaraja, Robert J. Norgard, Malay Haldar. Tumor-derived endothelins regulate antitumor immune responses through macrophage endothelin B receptor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1776.

Summary The immunosuppressive tumor microenvironment (TME) is a major barrier to immunotherapy. Within solid tumors, why monocytes preferentially differentiate into immunosuppressive tumor-associated macrophages (TAMs) rather than immunostimulatory dendritic cells (DCs) remains unclear. Using multiple murine sarcoma models, we find that the TME induces tumor cells to produce retinoic acid (RA), which polarizes intratumoral monocyte differentiation toward TAMs and away from DCs via suppression of DC-promoting transcription factor Irf4. Genetic inhibition of RA production in tumor cells or pharmacologic inhibition of RA signaling within TME increases stimulatory monocyte-derived cells, enhances T cell-dependent anti-tumor immunity, and synergizes with immune checkpoint blockade. Furthermore, an RA-responsive gene signature in human monocytes correlates with an immunosuppressive TME in multiple human tumors. RA has been considered as an anti-cancer agent, whereas our work demonstrates its tumorigenic capability via myeloid-mediated immune suppression and provides proof of concept for targeting this pathway for tumor immunotherapy.

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Emergency operations are associated with increased morbidity, mortality, and cost compared to elective operations. Palliative and emergent surgery for patients with advanced malignancies is associated with additional risk and remains controversial. Emergent or palliative interventions can be broadly categorized according to indication. Tumor related complications (bleeding, obstruction, or perforation) merit specific consideration, as do specific presentations such as pneumoperitoneum, pneumatosis intestinalis, or peritonitis from other causes that may arise during active therapy for malignancies. Although nonoperative, endoscopic, and interventional treatment modalities are frequently available, surgery remains the only effective therapy in selected situations such as small intestinal obstruction and tumor perforation. Selection of patients for surgery requires consideration of factors including overall prognosis, performance status, and patients' priorities. Selection and risk assessment tools underscore the limited capacity of patients' with higher risk features for durable recovery but do not supplant nuanced clinical judgment. J. Surg. Oncol. 2016;114:311-315. © 2016 Wiley Periodicals, Inc.

Tumor heterogeneity - resulting from genetic and epigenetic alterations acquired during tumor progression - is a critical driver of phenotypic diversity in most cancers. A lethal consequence of tumor heterogeneity is the acquisition of metastatic traits by tumor cells, leading to poor clinical outcomes. This remains a major problem in pancreatic ductal adenocarcinoma (PDAC), which continues to have the worst prognosis of any major cancer type. While most cases of PDAC present with metastatic disease at the time of diagnosis, the patterns and burden of metastasis can vary widely, with some patients exhibiting a limited metastatic burden while others have more extensive spread, which impacts clinical outcomes. However, the biological and functional differences that drive metastatic heterogeneity are poorly understood. One barrier to understanding metastatic heterogeneity has been a paucity of model systems that capture this natural variation and allow for direct assessment of paired primary tumors and metastases. We previously developed an autochthonous model of PDAC – the KPCX model – that employs multiplexed fluorescence-based labeling to track the contribution of multiple distinct tumor populations to metastasis. Importantly, this technique allows for ascertainment of primary-metastatic lineage relationships in vivo, so that primary tumor clones with substantial metastatic potential can be distinguished with those having poor metastatic potential. To understand the factors underlying differences in metastatic potential, we analyzed paired primary tumors and metastases in the KPCX model and from a cohort of 398 PDAC patients. Genomic and transcriptomic analysis of murine and human metastatic PDAC revealed an association between the highly metastatic state and gene amplification or transcriptional upregulation of MYC and its transcriptional targets. Functional assessments showed that MYC promotes metastasis by recruiting tumor associated macrophages (TAMs), leading to greater bloodstream intravasation. Consistent with these findings, metastatic progression in human PDAC was also associated of MYC signaling pathways and enrichment for MYC amplification in metastasis. Collectively, these results implicate MYC activity as a major determinant of metastatic burden and heterogeneity in advanced PDA. Citation Format: Ravikanth Maddipati, Robert J. Norgard, Timour Baslan, Komal S. Rathi, Amy Zhang, Pichai Raman, Max D. Wengyn, Taiji Yamazoe, Jinyang Li, David Balli, Michael J. LaRiviere, Ian W. Folkert, Ian D. Millstein, Jonathan Bermeo, Erica L. Carpenter, Scott Lowe, Christine Iacobuzio-Donahue, Faiyaz Notta, Ben Z. Stanger. MYC Influences metastatic heterogeneity in pancreatic cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2020 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2020;80(22 Suppl):Abstract nr PO-053.

Tumor heterogeneity - resulting from genetic and epigenetic alterations acquired during tumor progression - is a critical driver of phenotypic diversity in most cancers. A lethal consequence of tumor heterogeneity is the acquisition of metastatic traits by tumor cells, leading to poor clinical outcomes. This remains a major problem in pancreatic ductal adenocarcinoma (PDAC), which continues to have the worst prognosis of any major cancer type. While most cases of PDAC present with metastatic disease at the time of diagnosis, the patterns and burden of metastasis can vary widely, with some patients exhibiting a limited metastatic burden while others have more extensive spread, which impacts clinical outcomes. However, the biological and functional differences that drive metastatic heterogeneity are poorly understood. Citation Format: Ravikanth Maddipati, Robert J. Norgard, Timour Baslan, Komal S. Rathi, Amy Zhang, Pichai Raman, Max D. Wengyn, Taiji Yamazoe, Jinyang Li, David Balli, Michael LaRiviere, Ian W. Folkert, Ian D. Millstein, Jonathan Bermeo, Erica L. Carpenter, Scott Lowe, Christine Iacobuzio-Donahue, Faiyaz Notta, Ben Z. Stanger. MYC influences metastatic heterogeneity in pancreatic cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference on Tumor Heterogeneity: From Single Cells to Clinical Impact; 2020 Sep 17-18. Philadelphia (PA): AACR; Cancer Res 2020;80(21 Suppl):Abstract nr PO-071.

Summary: Activated macrophages must carefully calibrate their inflammatory responses to balance efficient pathogen control with inflammation-mediated tissue damage, but the molecular underpinnings of this “balancing act” remain unclear. Using genetically engineered mouse models and primary macrophage cultures, we show that Toll-like receptor (TLR) signaling induces the expression of the transcription factor Spic selectively in patrolling monocytes and tissue macrophages by a nuclear factor κB (NF-κB)-dependent mechanism. Functionally, Spic downregulates pro-inflammatory cytokines and promotes iron efflux by regulating ferroportin expression in activated macrophages. Notably, interferon-gamma blocks Spic expression in a STAT1-dependent manner. High levels of interferon-gamma are indicative of ongoing infection, and in its absence, activated macrophages appear to engage a “default” Spic-dependent anti-inflammatory pathway. We also provide evidence for the engagement of this pathway in sterile inflammation. Taken together, our findings uncover a pathway wherein counter-regulation of Spic by NF-κB and STATs attune inflammatory responses and iron metabolism in macrophages.

Rectal neuroendocrine tumors are often found incidentally. Local excision alone has been advocated for lesions ≤2 cm; however, the evidence base for this approach is limited.Associations among tumor size, degree of differentiation, and presence of distant metastatic disease were examined.This was a retrospective cohort study.This study was conducted using a nationwide cohort.A total of 4893 patients with rectal neuroendocrine tumors were identified in the National Cancer Database (2006-2015).Logistic regression analyses were used to evaluate associations among tumor size, degree of differentiation, and presence of regional and distant metastatic disease. Cut point analysis was performed to identify an optimal size threshold predictive of distant metastatic disease.Of patients included for analysis, 3880 (79.3%) had well-differentiated tumors, 540 (11.0%) had moderately differentiated tumors, and 473 (9.7%) had poorly differentiated tumors. On logistic regression, increasing size was associated with a higher likelihood of pathologically confirmed lymph node involvement (among patients undergoing proctectomy), and both size and degree of differentiation were independently associated with a higher likelihood of distant metastatic disease. The association between tumor size and distant metastatic disease was stronger for well-differentiated and moderately differentiated tumors (OR = 1.4; p0.001 for both) than for poorly differentiated tumors (OR = 1.1; p = 0.010). For well-differentiated tumors, the optimal cut point for the presence of distant metastatic disease was 1.15 cm (area under the curve = 0.88; 88% sensitive and 88% specific). Tumors ≥1.15 cm in diameter were associated with a substantially increased incidence of distant metastatic disease (72/449 (13.8%)). For moderately differentiated tumors, the optimal cut point was also 1.15 cm (area under the curve = 0.87, 100% sensitive and 75% specific).This study was limited by its retrospective design.Tumor size and degree of differentiation are predictive of regional and distant metastatic disease in rectal neuroendocrine tumors. Patients with tumors1.15 cm are at substantial risk of distant metastasis and should be staged and managed accordingly. See Video Abstract at http://links.lww.com/DCR/A778.

Urgent palliative surgery in the setting of advanced malignancy is associated with significant morbidity, mortality, and cost. Malignant bowel obstruction is the most frequent indication for such intervention. Traditional surgical dogma is often invoked to justify associated risks and cost, but little evidence exists to support surgical over nonsurgical approaches. Evolving evidence may provide more meaningful guidance for treatment selection.

Endoscopic full-thickness resection of gastrointestinal (GI) tumors has been applied to the management of premalignant, early malignant, and indolent tumors of the GI tract to spare morbidity associated with traditional surgical approaches. Increasingly, a combined laparoscopic-endoscopic approach is being used to treat lesions that are not amenable to endoscopic resection alone. Case reports and small case series have demonstrated utility for lesions such as gastric GI stromal tumors, early gastric carcinomas, small duodenal masses, and colonic polyps or masses. Although promising, further research is necessary to determine the best indications for such an approach, and to compare long-term outcomes to those achieved with more traditional approaches.

Emergency operations are associated with increased morbidity, mortality, and cost compared to elective operations. Palliative and emergent surgery for patients with advanced malignancies is associated with additional risk and remains controversial. Emergent or palliative interventions can be broadly categorized according to indication. Tumor related complications (bleeding, obstruction, or perforation) merit specific consideration, as do specific presentations such as pneumoperitoneum, pneumatosis intestinalis, or peritonitis from other causes that may arise during active therapy for malignancies. Although nonoperative, endoscopic, and interventional treatment modalities are frequently available, surgery remains the only effective therapy in selected situations such as small intestinal obstruction and tumor perforation. Selection of patients for surgery requires consideration of factors including overall prognosis, performance status, and patients' priorities. Selection and risk assessment tools underscore the limited capacity of patients' with higher risk features for durable recovery but do not supplant nuanced clinical judgment. J. Surg. Oncol. 2016;114:311-315. © 2016 Wiley Periodicals, Inc.

Objective Acute limb ischemia (ALI) is the cause of significant morbidity and mortality. Although ALI after cardiac surgery is associated with high rates of morbidity and mortality, there are no robust, controlled analyses of the risk factors and outcomes of ALI in this setting. We aimed to identify risk factors for and to delineate outcomes after ALI in patients undergoing cardiac surgery. Methods We performed a retrospective review of prospectively collected data on patients undergoing cardiac surgery at our institution between 2002 and 2012. Results Between 2002 and 2012, there were 11,343 patients who underwent major open cardiac surgery, with 156 cases of ALI for an incidence of 1.4%. In a multivariable model, significant risk factors for ALI included body surface area (odds ratio [OR], 0.41; 95% confidence interval [CI], 0.18-0.92), current smoking status (OR, 2.2; 95% CI, 1.3-3.7), peripheral arterial disease (OR, 2.5; 95% CI, 1.6-3.7), nonelective operative status (OR, 1.9-5.0; 95% CI, 1.2-19.7), use of extracorporeal membrane oxygenation (OR, 5.6; 95% CI, 2.5-11.6) or intra-aortic balloon pump (OR, 4.7; 95% CI, 2.9-7.5), and valve operation (OR, 2.1; 95% CI, 1.1-4.0). There were 105 (67%) patients who developed ALI who required an operation, and 27 (17%) required an amputation on the index admission. ALI was associated with a significant reduction in long-term survival (hazard ratio, 3.72; 95% CI, 2.97-4.65; P Conclusions ALI is associated with significant morbidity and mortality, and it is also associated with reduced long-term survival. Those patients with the risk factors described require extra vigilance to limit the risk of ALI and should be managed in accordance with the patient's overall clinical condition and goals of care.

Sarcomas are rare and heterogeneous cancer of mesenchymal origin. Treatment options have largely remained unchanged over decades and metastatic sarcoma is essentially incurable. There are more than 60 distinct diagnostic subtypes of sarcoma, many of which do not harbor consistent mutations. These factors make the development of targeted therapy particularly challenging in sarcomas. Therefore, a new therapeutic approach broadly targeting sarcomas of various subtypes is highly desirable. Immunotherapy offers a viable approach in cancer treatment, which has not been adequately explored in sarcomas. The immune system can distinguish malignant from normal cells and mount an antitumor T-cell response. However, tumors create a highly immunosuppressive microenvironment, which counteracts both endogenous as well as therapy-induced antitumor immune responses. Therefore, understanding the cellular and molecular basis of immunosuppression in sarcoma microenvironment is important for the development and success of any immunotherapeutic approach. Macrophages (MACs) and dendritic cells (DC) are antigen-presenting cells (APC) of the innate immune system that play key role in shaping immune responses. Studies in carcinomas have shown that immunosuppressive MACs greatly outnumber immunostimulatory DCs in the tumor microenvironment. Currently, it is unclear whether sarcomas also harbor such polarized distribution of APC in their microenvironment. Tumor-associated MACs can develop from circulating monocytes or from preexisting tissue macrophages. Likewise, DCs can develop from circulating monocytes or bone marrow-derived precursors. However, the origin of sarcoma-infiltrating MACs and DCs is unclear. Insights into the distribution and origin of tumor-infiltrating APCs is critical for devising therapeutic approaches targeting these cells to counteract immunosuppression in tumor microenvironment. We have addressed this issue by using several distinct murine models of sarcomas. Based on genetic background sarcomas can be divided into (1) translocation-associated sarcomas, (2) sarcomas harboring mutations in oncogenes and tumor suppressors, and (3) sarcomas with complex karyotypes displaying significant genomic instability. We selected one murine model to represent each of the three subtypes. An SYT-SSX fusion oncogene-driven mouse model of synovial sarcoma represented group 1, loss of P53 coupled with activation of oncogenic KRAS-driven mouse model of undifferentiated pleomorphic sarcoma represented group 2, and syngeneic transplant of sarcoma cell lines derived from methylcholanthrene-induced fibrosarcomas represented group 3. In all three murine models, APCs were found to comprise the majority of leukocyte infiltrates in tumors. Using multiparametric flow cytometry, gene-expression profiling, and lineage labeling we found that the vast majority of APCs in sarcoma were MACs with DCs comprising a very small subset. Next, using a combination of in vivo lineage tracing and lineage ablation we uncovered that the majority of MACs and DCs were derived from circulating monocytes. These results suggest that monocytes preferentially differentiate into macrophages but not DCs in sarcoma microenvironment. These findings lay the groundwork for future efforts in our laboratory aimed at understanding the molecular basis for such polarized macrophage differentiation in the tumor microenvironment. The overarching goal is to translate our findings into therapeutic approaches aimed at increasing the frequency of immunostimulatory DCs while reducing immunosuppressive MACs in sarcoma microenvironment. The clinical benefits of such an approach will be two-fold: (1) reduced immunosuppression in the tumor microenvironment increasing the efficacy of therapeutically generated T cells, and (2) increased probability of generating endogenous antitumor immune responses via the activity of DCs in the tumor microenvironment. Citation Format: Samir Devalaraja, Ian Folkert, Minghong Li, Yuma Tada, Kanika Jain, Malay Haldar. Sarcoma microenvironment blocks DC but promotes macrophage differentiation from tumor-infiltrating monocytes [abstract]. In: Proceedings of the AACR Conference on Advances in Sarcomas: From Basic Science to Clinical Translation; May 16-19, 2017; Philadelphia, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(2_Suppl):Abstract nr B26.

Pancreatic neuroendocrine tumors (PNETs) are a rare and diverse group of tumors; nonfunctional (NF) PNETs account for the majority of cases. Most patients with NF-PNETs have metastatic disease at the time of presentation. A variety of treatment modalities exist, including medical, liver directed, and surgical treatments. Aggressive surgical management is associated with prolonged survival, however available data are limited by selection bias and the frequent combination of PNETs with carcinoid tumors. Although few patients with metastatic disease will be cured, application of currently available therapies in a multidisciplinary setting can lead to excellent outcomes with prolonged patient survival.