Abstract A56: Targeting eIF4A dependent translation as therapeutics in pancreatic cancer

Pancreatic cancer is one of the most aggressive cancers with no targeted therapy available. RNA translation is activated in aggressive pancreatic cancer and at the same time is also refractory to mTor inhibition. We have used a translation inhibitor for eIF4A, RNA helicase that is downstream of mTOR signaling and can be functionally targeted in pancreatic cancer. We establish that Silvestrol and its analog CR-31B showed potent anti-tumor activity in pancreatic cancer cell lines in vitro and in vivo. Silvestrol/CR-31B reduced pancreatic cancer cells and organoids growth derived from mouse model of pancreatic cancer and human patient samples in vitro. Further we identify the genome wide translational targets of Silvestrol in pancreatic cancer cell line that lacks response to mTOR signaling through loss of EIF4EBP1. Silvestrol down regulate translation of many key oncogenes and others cellular factors involved in oncogenic signaling in pancreatic cancer. Silvestrol targets were also enriched for G-quadruplex structure in their 5’UTR. With this study we establish a new mechanism of targeting pancreatic cancer cells through translation inhibition and identify more proteins as therapeutic targets that are regulated independent of mTOR signaling.

Citation Format: Kamini Singh, Stefan G. Stark, Agnes Viale, Prathibha Mohan, Man Jiang, Gunnar Rätsch, Hans-Guido Wendel.{Authors}. Targeting eIF4A dependent translation as therapeutics in pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr A56.

Phase I Study of Epigenetic Priming with Azacitidine Prior to Standard Neoadjuvant Chemotherapy for Patients with Resectable Gastric and Esophageal Adenocarcinoma: Evidence of Tumor Hypomethylation as an Indicator of Major Histopathologic Response

Purpose: Epigenetic silencing of tumor suppressor genes (TSG) is an acquired abnormality observed in cancer and is prototypically linked to DNA methylation. We postulated that pretreatment (priming) with 5-azacitidine would increase the efficacy of chemotherapy by reactivating TSGs. This study was conducted to identify a tolerable dose of 5-azacitidine prior to EOX (epirubicin, oxaliplatin, capecitabine) neoadjuvant chemotherapy in patients with locally advanced esophageal/gastric adenocarcinoma (EGC).Experimental Design: Eligible patients had untreated, locally advanced, resectable EGC, ECOG 0-2, and adequate organ function. 5-Azacitidine (V, 75 mg/m²) was given subcutaneously for 3 (dose level, DL 1) or 5 (DL 2) days prior to each 21-day cycle of EOX (E, 50 mg/m²; O, 130 mg/m²; X, 625 mg/m² twice daily for 21 days). Standard 3+3 methodology guided V dose escalation. DNA methylation at control and biomarker regions was measured by digital droplet, bisulfite qPCR in tumor samples collected at baseline and at resection.Results: All subjects underwent complete resection of residual tumor (R0). Three of the 12 patients (25%) achieved a surgical complete response and 5 had partial responses. The overall response rate was 67%. The most common toxicities were gastrointestinal and hematologic. Hypomethylation of biomarker genes was observed at all dose levels and trended with therapeutic response.Conclusions: Neoadjuvant VEOX was well-tolerated with significant clinical and epigenetic responses, with preliminary evidence that priming with V prior to chemotherapy may augment chemotherapy efficacy. The recommended phase II trial schedule is 5-azacitidine 75 mg/m² for 5 days followed by EOX chemotherapy every 21 days. Clin Cancer Res; 23(11); 2673-80. ©2016 AACR.

Abstract PR09: Identifying the epigenetic code of tumor-specific CD8 T cell dysfunction and therapeutic reprogramming

Mutant neoantigens are commonly expressed in human solid tumors, and CD8 T cells specific for such antigens are detected in cancer patients. However, we know that these tumor-specific T cells are non-functional because despite their presence, tumors progress and often eventually cause death. Distinct T cell differentiation states are associated with specific epigenetic states that define the T cell's functional and phenotypic properties. It is currently not known what epigenetic changes establish and regulate tumor-specific CD8 T cell dysfunction and whether specific epigenetic modifications in dysfunctional T cells determine the ability to respond to therapeutic interventions such as checkpoint blockade (PD-1 and CTLA-4). Here, for the first time, we (1) characterize the progressive chromatin remodeling underlying T cell differentiation to the dysfunctional state in mouse and human tumors, and (2) provide insights into the epigenetic and transcriptional regulatory mechanisms determining T cell susceptibility to therapeutic reprogramming.

Using a genetic cancer mouse model in which tamoxifen treatment induces expression of an oncogenic driver neoantigen, SV40 large T antigen (Tag), we previously showed that tumor-specific CD8 T cells (TCRSV40-I) become unresponsive early during tumorigenesis, even before the emergence of a pathologically-defined malignant tumor (pre-malignant phase). While CD8 T cell dysfunction was initially reversible, it ultimately became a fixed state that could not be rescued by therapeutic interventions such as PD1 checkpoint blockade.

To identify the hierarchical changes in chromatin states resulting in “dysfunction imprinting,” we used the “Assay for Transposase-Accessible Chromatin using Sequencing” (ATAC-Seq) to map the genome-wide changes in chromatin accessibility in TCRSV40-I cells over the course of tumor development. In parallel, we carried our RNA-Seq on all samples to determine the interplay between chromatin remodeling and transcriptional networks. Substantial chromatin remodeling occurred during early T cell activation in the pre-malignant lesion (day 5), followed by a second wave of chromatin accessibility changes between day 7 and 14. Strikingly, after the second wave, no further CD8 T cell chromatin remodeling occurred during tumorigenesis, even after progression to an advanced late-stage tumor with an immunosuppressive microenvironment. Interestingly, these 2 distinct chromatin accessibility patterns (states 1 and 2) in dysfunctional TCRSV40-I correlated temporally with the plastic and fixed dysfunctional states and susceptibility to therapeutic reprogramming in vivo. To understand the transition from plastic to imprinted dysfunction, we analyzed the differential expression of transcription factors (TF) in conjunction with changes in peak accessibility at TF-binding motifs genome-wide. We identified a network including CD8 T cell regulatory TF such as TCF1, LEF1, BLIMP1, and BACH2 as well as less-well-characterized TF (NR4A2, TOX) potentially controlling differentiation to the dysfunctional state. Moreover, ATAC-Seq analysis of human tumor-infiltrating CD8 T cells revealed similar tumor-associated changes in peak accessibility, and studies are ongoing to assess the associated TF networks.

In this study, we have defined discrete chromatin states and associated transcriptional networks underlying plastic and fixed dysfunction in tumor-specific T cells, thus providing new insights into the genomic control circuitry of T cell differentiation/dysfunction that may point to new strategies for cellular reprogramming of T cells for cancer immunotherapy.

Citation Format: Mary Philip, Lauren Fairchild, Liping Sun, Agnes Viale, Steven Camara, Ellen Horste, Taha Merghoub, Jedd D. Wolchok, Christina S. Leslie, Andrea Schietinger. Identifying the epigenetic code of tumor-specific CD8 T cell dysfunction and therapeutic reprogramming [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr PR09.

Targeted massively parallel sequencing of angiosarcomas reveals frequent activation of the mitogen activated protein kinase pathway

Angiosarcomas are rare malignant mesenchymal tumors of endothelial differentiation. The clinical behavior is usually aggressive and the prognosis for patients with advanced disease is poor with no effective therapies. The genetic bases of these tumors have been partially revealed in recent studies reporting genetic alterations such as amplifications of MYC (primarily in radiation-associated angiosarcomas), inactivating mutations in PTPRB and R707Q hotspot mutations of PLCG1. Here, we performed a comprehensive genomic analysis of 34 angiosarcomas using a clinically-approved, hybridization-based targeted next-generation sequencing assay for 341 well-established oncogenes and tumor suppressor genes. Over half of the angiosarcomas (n = 18, 53%) harbored genetic alterations affecting the MAPK pathway, involving mutations in KRAS, HRAS, NRAS, BRAF, MAPK1 and NF1, or amplifications in MAPK1/CRKL, CRAF or BRAF. The most frequently detected genetic aberrations were mutations in TP53 in 12 tumors(35%) and losses of CDKN2A in9 tumors (26%). MYC amplifications were generally mutually exclusive of TP53 alterations and CDKN2A loss and were identified in 8 tumors (24%), most of which (n = 7, 88%) arose post-irradiation. Previously reported mutations in PTPRB (n = 10, 29%) and one (3%) PLCG1 R707Q mutation were also identified. Our results demonstrate that angiosarcomas are a genetically heterogeneous group of tumors, harboring a wide range of genetic alterations. The high frequency of genetic events affecting the MAPK pathway suggests that targeted therapies inhibiting MAPK signaling may be promising therapeutic avenues in patients with advanced angiosarcomas.

Abstract LB-320: Obligate lesions and diverse evolutionary patterns drive small cell bladder cancer

Small cell bladder cancer (SCBC) is a rare and aggressive neuroendocrine tumor with a dismal prognosis and limited treatment options. As SCBC is histologically indistinguishable from small cell lung cancer, a shared pathogenesis and cell of origin has been proposed. To determine whether SCBCs arise from a pre-existent urothelial carcinoma or share a molecular pathogenesis in common with small cell lung cancer, we performed integrative analysis of 61 SCBC patients to identify histology- and organ-specific similarities and differences with urothelial carcinomas and small cell lung cancers. SCBC has a high somatic mutational burden driven predominantly by an APOBEC-mediated mutational process. Obligate mutations in TP53, RB1, or the TERT promoter were present in nearly all samples. While these events arose early in all affected tumors, reflecting an evolutionary branch point that drove small cell lineage differentiation, they were not the founding transforming event, as they were often preceded by diverse and less common driver mutations many of which are common in bladder urothelial cancers but not small cell lung tumors. The majority of patient tumors (72%) also underwent whole-genome duplication (WGD). While arising at different chronological points in the evolution of the disease, WGD was often preceded by biallelic mutations in TP53 with retention of two intact copies. Together, our findings indicate that small cell cancers of the bladder and lung have a convergent but distinct pathogenesis and SCBCs likely arise from a cell of original shared with urothelial bladder cancer.

Citation Format: Alexander Penson, Matthew T. Chang, Neil Desai, Nicholas D. Socci, Ronglai Shen, Venkatraman E. Seshan, Ritika Kundra, Adam Abeshouse, Agnes Viale, Eugene K. Cha, Bernard H. Bochner, Jonathan E. Rosenberg, Dean F. Bajorin, Nikolaus Schultz, Michael F. Berger, Gopa Iyer, David B. Solit, Hikmat Al-Ahmadie, Barry S. Taylor. Obligate lesions and diverse evolutionary patterns drive small cell bladder cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-320.

KRAS AND THE REALITY OF PERSONALIZED MEDICINE IN NON-SMALL CELL LUNG CANCER

Lung cancer is the leading cause of mortality among all cancer types, worldwide. Latest available global statistics of World Health Organization report 1.59 million casualities in 2012 alone. Worldwide, 1 in 5 cancer deaths are caused by lung cancer. In 2016, in USA alone, estimated new cases of lung cancer are 224,390, of which 158,080 are expected to result in death as reported by National Cancer Institute. Non-small cell lung cancer (NSCLC), a histological subtype, comprises of about 85% of all cases, which is nearly 9 out of 10 lung cancer patients. Efforts are underway to develop and improve targeted therapy strategies. Certain mutations are being clinically targeted such as those in EGFR and ALK genes. However, one of the most frequently mutated genes in NSCLC is the KRAS oncogene, which is currently untargetable. Approximately 25% of all types of NSCLC tumors contain KRAS mutations, which remain as an undruggable challenge. These mutations are indicative of poor prognosis and confer negative response to standard chemotherapy. Furthermore, tumors harboring KRAS mutations are unlikely to respond to currently available targeted treatments such as Tyrosine Kinase Inhibitors. Therefore, there is a definitive, urgent need to generate new targeted therapy approaches for KRAS mutations. Current strategies have major limitations and evolve around targeting molecules upstream and downstream of KRAS. Direct targeting is not available in the clinic. Combination therapies of multiple agents are being sought. Concentrated efforts are needed to accelerate basic research and consecutive clinical trials to achieve effective targeting of KRAS.

Evaluating Cancer of the Central Nervous System Through Next-Generation Sequencing of Cerebrospinal Fluid

PURPOSE

Cancer spread to the central nervous system (CNS) often is diagnosed late and is unresponsive to therapy. Mechanisms of tumor dissemination and evolution within the CNS are largely unknown because of limited access to tumor tissue.

MATERIALS AND METHODS

We sequenced 341 cancer-associated genes in cell-free DNA from cerebrospinal fluid (CSF) obtained through routine lumbar puncture in 53 patients with suspected or known CNS involvement by cancer.

RESULTS

We detected high-confidence somatic alterations in 63% (20 of 32) of patients with CNS metastases of solid tumors, 50% (six of 12) of patients with primary brain tumors, and 0% (zero of nine) of patients without CNS involvement by cancer. Several patients with tumor progression in the CNS during therapy with inhibitors of oncogenic kinases harbored mutations in the kinase target or kinase bypass pathways. In patients with glioma, the most common malignant primary brain tumor in adults, examination of cell-free DNA uncovered patterns of tumor evolution, including temozolomide-associated mutations.

CONCLUSION

The study shows that CSF harbors clinically relevant genomic alterations in patients with CNS cancers and should be considered for liquid biopsies to monitor tumor evolution in the CNS.

Deciphering the epigenetic programming underlying CD8 T cell dysfunction in solid tumors

Tumor-specific CD8 T cells in progressive solid tumors express inhibitory receptors and fail to proliferate and produce effector cytokines. Using a mouse model (ASTxCre-ERT2) in which tamoxifen (TAM) treatment induces an oncogenic driver neoantigen, SV40 large T antigen (Tag) in hepatocytes, we previously showed that tumor-specific CD8 T cells (TCRSV40-I) become unresponsive quite early during the pre-/early malignant phase. While the dysfunctional state is initially plastic, TCRSV40-I cells soon enter a fixed dysfunctional state with the phenotypic, functional, and molecular hallmarks of T cells from late-stage human tumors. To define the epigenetic programs associated with plasticity and imprinting of tumor-specific T cell dysfunction, we used the “Assay for Transposase-Accessible Chromatin using Sequencing” (ATAC-Seq) to map chromatin accessibility in TCRSV40-I cells isolated from pre/early malignant lesions as well as in TCRSV40-I differentiating to the normal effector and memory states. Chromatin accessibility changes underlying TCRSV40-I activation and differentiation in pre-malignant lesions diverged from that in normal differentiation, and we observed 2 distinct chromatin accessibility patterns in dysfunctional TCRSV40-I correlating with the plastic and fixed dysfunctional states. Surprisingly, memory TCRSV40-I transferred into mice with late-stage established Tag-expressing hepatocellular carcinomas displayed these same 2 chromatin accessibility profiles, thus regardless of the initial CD8 T cell epigenetic state, epigenetic remodeling drives tumor-specific T cell differentiation to the dysfunctional state in both pre-malignant lesions and late established solid tumors.

Abstract S4-04: Lobular carcinoma in situ displays intra-lesion genetic heterogeneity and its progression to invasive disease involves clonal selection and variations in mutational processes

Introduction: Lobular carcinoma in situ (LCIS) is considered both a risk factor and non-obligate precursor of invasive breast cancer. We sought to determine the genomic landscape of LCIS and the mutational processes involved in the clonal evolution and progression from LCIS to ductal carcinoma in situ (DCIS) and invasive lobular carcinoma (ILC).

Methods: Patients with a history of LCIS undergoing therapeutic or prophylactic mastectomy were prospectively enrolled in an IRB approved protocol. Frozen tissue blocks were collected, screened for lesions of interest (LCIS, DCIS, ILC, invasive ductal carcinomas (IDC)) and subjected to microdissection and DNA/RNA extraction. Matched germline DNA was available for all cases. Whole exome sequencing was performed on a HiSeq2000 and data were aligned to the reference human genome and processed using GATK. Single nucleotide variants (SNVs) and small insertions/deletions were identified using MuTect and Varscan, respectively. Purity and ploidy estimates were calculated using ABSOLUTE. Clonal frequencies were estimated using Pyclone and the clonal structure of each sample was reconstructed using SubcloneSeeker. Shannon index and Simpson index metrics were used to calculate heterogeneity levels. Mutational signatures were defined according to their mutational trinucleotide context, and the expression levels of APOBEC gene family members were assessed by quantitative reverse transcription (qRT)-PCR.

Results: 30 LCIS, 10 ILCs, 7 DCIS and 5 IDCs from 15 patients qualified for data analysis. CDH1 was the most frequently mutated gene and found to be targeted by mutations in 26 LCIS samples (23 somatic, 3 germline). The repertoire of somatic mutations in LCIS was similar to that of luminal A breast cancers, with the exception of the significantly higher frequency of CDH1 mutations and the lower prevalence of TP53 mutations. ILCs were clonally related to at least one LCIS in 10 patients, and in 3/7 patients, DCIS was clonally related to at least one LCIS. Clonal composition analysis revealed that the presence of a minor clone(s) in LCIS, and the levels of intra-tumor genetic heterogeneity were significantly higher in LCIS clonally related with DCIS/ILC than in LCIS unrelated to DCIS/ILC. In two cases, a minor LCIS subclone constituted the major clone in the associated DCIS/ILC. A comparative analysis of the mutational signatures in the truncal and branch mutations of these cases revealed that whilst the truncal mutations displayed an aging signature, branch mutations were enriched for the APOBEC signature. qRT-PCR analysis demonstrated that cases displaying the APOBEC signature also harbored significantly higher levels of APOBEC3B expression than samples with the aging signature.

Conclusions: LCIS displays intra-lesion genetic heterogeneity, and the progression from LCIS to DCIS or ILC may involve the selection of clones resulting from distinct mutational processes during clonal evolution. Our findings also suggest that cytodine deamination driven by the overexpression of APOBEC3B may drive the progression of LCIS to DCIS/ILC in a subset of cases.

Citation Format: Reis-Filho JS, Schizas M, Piscuoglio S, Sakr RA, Ng CKY, Lim RS, Carniello JVS, Towers R, Martelotto L, Giri DD, de Andrade VP, Viale A, Solit DB, Weigelt B, King TA. Lobular carcinoma in situ displays intra-lesion genetic heterogeneity and its progression to invasive disease involves clonal selection and variations in mutational processes. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr S4-04.

Abstract P2-01-02: Capturing intra-tumor genetic heterogeneity in cell-free plasma DNA from patients with oligometastatic breast cancer

Background: The analysis of cell-free tumor DNA (ctDNA) from plasma has been heralded as a non-invasive technique for disease monitoring and as a means to overcome the challenges posed by intra-tumor genetic heterogeneity. ctDNA levels have been shown to correlate with tumor burden in breast cancer patients. Hence, we sought to define whether massively parallel sequencing of cell-free plasma DNA would capture the entire repertoire of somatic mutations present in the primary tumors and/ or metastases from patients with oligometastatic breast cancer.

Methods: Frozen diagnostic biopsies from primary tumors and their distant metastases were obtained from five prospectively accrued treatment-naïve patients with stage IV breast cancer at presentation (1 estrogen receptor (ER)+/HER2+, 2 ER+/HER2-, 2 ER-/HER2+). A second, independent formalin-fixed paraffin-embedded (FFPE) diagnostic biopsy was obtained from the primary tumor and metastasis from 4 patients. Plasma samples were obtained from all patients. DNA samples from microdissected frozen tumors and peripheral blood, as well as plasma from one patient, were subjected to high-depth whole exome sequencing. DNA samples from all biopsies (frozen/FFPE), plasma and peripheral blood were subjected to targeted capture massively parallel sequencing, with baits for all somatic mutations detected by whole exome sequencing and all exons of the 100 genes most frequently mutated in breast cancer. Driver mutations were defined by state-of-the-art bioinformatic methods and literature search.

Results: We identified and confirmed a median of 54 (range 25-75) and 53 (range 26-85) non-synonymous mutations in the primary tumors and metastases from the 5 cases analyzed, respectively. By sequencing the plasma DNA to a median depth of 248x (range 92-431x), state-of-the-art mutation callers revealed 0-4 mutations (0%-8% of mutations) per patient, and direct interrogation of the sequencing data, based on prior knowledge of the mutations present in the lesions, resulted in the identification of 2-18 mutations (3%-38% of mutations) per patient. Of the bona fide driver mutations, 2/3 TP53 mutations, 0/1 PIK3CA hotspot mutation, 0/1 BRCA2 frameshift mutation, 0/1 GATA3 frameshift mutation and 0/1 ERBB3 activating mutation were captured in the plasma DNA. A SMAD4 pathogenic mutation and a TCF7L2 truncating mutation were found in two diagnostic biopsies of metastatic lesions but not in two biopsies of the primary tumors in one patient each. Whilst the SMAD4 mutation was detected in the plasma DNA from the respective patient, the TCF7L2 mutation was not. Of the 62 mutations restricted to the primary tumors (0-42 per patient) and 74 restricted to the metastatic tumors (1-41 per patient), 4 and 7, respectively, were captured in the plasma DNA.

Conclusions: Massively parallel sequencing assessment of plasma DNA allows for the identification of mutations found in primary tumors and/ or their metastases, however, only a subset of these could be detected at up to 431x depth. These observations suggest that current approaches for whole exome or targeted massively parallel sequencing may not be sufficient to capture the genetic heterogeneity of breast cancers in patients with oligometastatic disease.

Citation Format: Ng CKY, Bidard F-C, Piscuoglio S, Lim RS, Pierga J-Y, Cottu P, Vincent-Salomon A, Viale A, Norton L, Sigal B, Weigelt B, Reis-Filho JS. Capturing intra-tumor genetic heterogeneity in cell-free plasma DNA from patients with oligometastatic breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-01-02.

Intestinal microbiome analyses identify melanoma patients at risk for checkpoint-blockade-induced colitis

The composition of the intestinal microbiota influences the development of inflammatory disorders. However, associating inflammatory diseases with specific microbial members of the microbiota is challenging, because clinically detectable inflammation and its treatment can alter the microbiota's composition. Immunologic checkpoint blockade with ipilimumab, a monoclonal antibody that blocks cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) signalling, is associated with new-onset, immune-mediated colitis. Here we conduct a prospective study of patients with metastatic melanoma undergoing ipilimumab treatment and correlate the pre-inflammation faecal microbiota and microbiome composition with subsequent colitis development. We demonstrate that increased representation of bacteria belonging to the Bacteroidetes phylum is correlated with resistance to the development of checkpoint-blockade-induced colitis. Furthermore, a paucity of genetic pathways involved in polyamine transport and B vitamin biosynthesis is associated with an increased risk of colitis. Identification of these biomarkers may enable interventions to reduce the risk of inflammatory complications following cancer immunotherapy.

A subset of cancer patients treated with immune checkpoint blockade develops colitis. Here the authors show that lower abundance of Bacteroidetes and vitamin B biosynthetic modules in fecal samples of melanoma patients can predict their susceptibility to colitis following anti-CTLA-4 treatment.

Massively Parallel Sequencing-Based Clonality Analysis of Synchronous Endometrioid Endometrial and Ovarian Carcinomas

Synchronous early-stage endometrioid endometrial carcinomas (EECs) and endometrioid ovarian carcinomas (EOCs) are associated with a favorable prognosis and have been suggested to represent independent primary tumors rather than metastatic disease. We subjected sporadic synchronous EECs/EOCs from five patients to whole-exome massively parallel sequencing, which revealed that the EEC and EOC of each case displayed strikingly similar repertoires of somatic mutations and gene copy number alterations. Despite the presence of mutations restricted to the EEC or EOC in each case, we observed that the mutational processes that shaped their respective genomes were consistent. High-depth targeted massively parallel sequencing of sporadic synchronous EECs/EOCs from 17 additional patients confirmed that these lesions are clonally related. In an additional Lynch Syndrome case, however, the EEC and EOC were found to constitute independent cancers lacking somatic mutations in common. Taken together, sporadic synchronous EECs/EOCs are clonally related and likely constitute dissemination from one site to the other.

Abstract B14: Molecular characterization of mucinous ovarian carcinoma

Mucinous ovarian carcinoma (MOC) is a rare, chemoresistant tumor known to share pathologic features with tumors of the gastrointestinal and pancreaticobiliary tracts. To better understand the genomic and proteomic landscapes of invasive MOCs, we identified somatic mutations and proteins expression in a single institution cohort and compared these results with data from TCGA tumor projects.

Twenty-six tumors consistent with primary invasive MOC after expert pathology review and with available paired tumor and normal tissue were identified from institutional databases between July 2001 and July 2012. DNA extracted from FFPE or fresh frozen samples underwent next generation sequencing with a combination of a candidate gene assay (37 genes), the MSK-IMPACT assay (341 genes), transcriptome sequencing, and whole exome sequencing. Copy number alterations were identified using data from the MSK-IMPACT assay, whole exome sequencing or Affymetrix SNP 6.0 arrays. Immunohistochemistry (IHC) was performed using optimized antibodies for six proteins to confirm the diagnosis of MOC (ER, PR, CK7, CK20, CDX-2, PAX8) and seven proteins to correlate with mutation status and copy number alterations (p53, ARID1A[Baf250a], PTEN, PMS2, MSH6, HER2, p16). Mutation data for other TCGA tumor types was obtained from the cBio Cancer Genomics Portal (cbioportal.org).

The median age of the cohort was 58 years (range 20-86 years). Most (19/26, 73%) of the tumors were stage I. Somatic TP53 and KRAS mutations were the most common seen and were identified in 18 (69%) cases each, with a co-mutation rate of 50% (13/26). Other commonly mutated genes include ARID1A, PTEN, and PIK3CA. Homozygous deletions of CDKN2A were found in 27% (7/26). ERBB2 alterations were identified in 19% (5/26) and consisted of three amplifications and two mutations. Mutations in at least one potentially targetable gene were identified in 42% (11/26) of tumors. IHC was concordant with sequencing results in 154/182 (85%) of stained cases. Pancreatic, colorectal, lung adenocarcinoma, endometrial, and stomach cancers have the highest frequency of KRAS mutations. Co-mutations of KRAS and TP53 occur most commonly in pancreatic (59%) and colorectal (21%) carcinomas. CDKN2A homozygous deletions are also found at a similar frequency in pancreatic adenocarcinomas (28%). When evaluating the mutation rates of the five most commonly mutated genes in our MOC cohort with colorectal, pancreatic, gastric and high-grade serous ovarian carcinomas (HGSOC) in the TCGA datasets, pancreatic adenocarcinoma showed the most similarity. HGSOC showed little similarity to the MOCs.

KRAS and TP53 co-mutation are common in invasive MOCs. Other commonly mutated genes include ARID1A, PTEN, and PIK3CA. Potentially targetable ERBB2 alterations were identified in several cases. Despite anatomic distinctions, the mutational landscape of MOC shares similarities with that of pancreatic adenocarcinoma including frequent CDKN2A deletions and KRAS/TP53 co-mutation. The suggested shared molecular pattern with pancreatic adenocarcinoma offers potential to guide future developmental therapeutics.

Citation Format: Brooke Schlappe, Jennifer J. Mueller, Narciso Olvera, Fanny Dao, Cyriac Kandoth, Faina Bogomolniy, Agnes Viale, Kety Huberman, Gouri Nanjangud, Yaser Hussein, Barry Taylor, Robert Soslow, Douglas A. Levine. Molecular characterization of mucinous ovarian carcinoma. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: Exploiting Vulnerabilities; Oct 17-20, 2015; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(2 Suppl):Abstract nr B14.

A Validated Prognostic Multigene Expression Assay for Overall Survival in Resected Colorectal Cancer Liver Metastases

PURPOSE

Risk stratification after surgery for colorectal cancer liver metastases (CRLM) is achieved using clinicopathologic variables, however, is of limited accuracy. We sought to derive and externally validate a multigene expression assay prognostic of overall survival (OS) that is superior to clinicopathologic variables in patients with surgically resected CRLM.

EXPERIMENTAL DESIGN

We measured mRNA expression in prospectively collected frozen tumor from 96 patients with surgically resected CRLM at Memorial Sloan Kettering Cancer Center (MSKCC, New York, NY). We retrospectively generated a 20-gene molecular risk score (MRS) and compared its prognostic utility for OS and recurrence-free survival (RFS) with three common clinical risk scores (CRS). We then tested the prognostic ability of the MRS in an external validation cohort (European) of 119 patients with surgically resected CRLM at the University Medical Center Utrecht (Utrecht, the Netherlands) and Paul Brousse Hospital (Villejuif, France).

RESULTS

For OS in the MSKCC cohort, MRS was the strongest independent prognosticator (HR, 3.7-4.9; P < 0.001) followed by adjuvant chemotherapy (HR, 0.3; P ≤ 0.001). For OS in the European cohort, MRS was the only independent prognosticator (HR, 3.5; P = 0.007). For RFS, MRS was also independently prognostic in the MSKCC cohort (HR, 2.4-2.6; P ≤ 0.001) and the European cohort (HR, 1.6-2.5; P ≤ 0.05).

CONCLUSIONS

Compared with CRSs, the MRS is more accurate, broadly applicable, and an independent prognostic biomarker of OS in resected CRLM. This MRS is the first externally validated prognostic multigene expression assay after metastasectomy for CRLM and warrants prospective validation. Clin Cancer Res; 22(10); 2575-82. ©2016 AACR.

NF2 Loss Promotes Oncogenic RAS-Induced Thyroid Cancers via YAP-Dependent Transactivation of RAS Proteins and Sensitizes Them to MEK Inhibition

Ch22q LOH is preferentially associated with RAS mutations in papillary and in poorly differentiated thyroid cancer (PDTC). The 22q tumor suppressor NF2, encoding merlin, is implicated in this interaction because of its frequent loss of function in human thyroid cancer cell lines. Nf2 deletion or Hras mutation is insufficient for transformation, whereas their combined disruption leads to murine PDTC with increased MAPK signaling. Merlin loss induces RAS signaling in part through inactivation of Hippo, which activates a YAP-TEAD transcriptional program. We find that the three RAS genes are themselves YAP-TEAD1 transcriptional targets, providing a novel mechanism of promotion of RAS-induced tumorigenesis. Moreover, pharmacologic disruption of YAP-TEAD with verteporfin blocks RAS transcription and signaling and inhibits cell growth. The increased MAPK output generated by NF2 loss in RAS-mutant cancers may inform therapeutic strategies, as it generates greater dependency on the MAPK pathway for viability.

SIGNIFICANCE

Intensification of mutant RAS signaling through copy-number imbalances is commonly associated with transformation. We show that NF2/merlin inactivation augments mutant RAS signaling by promoting YAP/TEAD-driven transcription of oncogenic and wild-type RAS, resulting in greater MAPK output and increased sensitivity to MEK inhibitors.

Interrogation of a context-specific transcription factor network identifies novel regulators of pluripotency

The predominant view of pluripotency regulation proposes a stable ground state with coordinated expression of key transcription factors (TFs) that prohibit differentiation. Another perspective suggests a more complexly regulated state involving competition between multiple lineage-specifying TFs that define pluripotency. These contrasting views were developed from extensive analyses of TFs in pluripotent cells in vitro. An experimentally validated, genome-wide repertoire of the regulatory interactions that control pluripotency within the in vivo cellular contexts is yet to be developed. To address this limitation, we assembled a TF interactome of adult human male germ cell tumors (GCTs) using the Algorithm for the Accurate Reconstruction of Cellular Pathways (ARACNe) to analyze gene expression profiles of 141 tumors comprising pluripotent and differentiated subsets. The network (GCT(Net)) comprised 1,305 TFs, and its ingenuity pathway analysis identified pluripotency and embryonal development as the top functional pathways. We experimentally validated GCT(Net) by functional (silencing) and biochemical (ChIP-seq) analysis of the core pluripotency regulatory TFs POU5F1, NANOG, and SOX2 in relation to their targets predicted by ARACNe. To define the extent of the in vivo pluripotency network in this system, we ranked all TFs in the GCT(Net) according to sharing of ARACNe-predicted targets with those of POU5F1 and NANOG using an odds-ratio analysis method. To validate this network, we silenced the top 10 TFs in the network in H9 embryonic stem cells. Silencing of each led to downregulation of pluripotency and induction of lineage; 7 of the 10 TFs were identified as pluripotency regulators for the first time.

Extreme Outlier Analysis Identifies Occult Mitogen-Activated Protein Kinase Pathway Mutations in Patients With Low-Grade Serous Ovarian Cancer

PURPOSE

No effective systemic therapy exists for patients with metastatic low-grade serous (LGS) ovarian cancers. BRAF and KRAS mutations are common in serous borderline (SB) and LGS ovarian cancers, and MEK inhibition has been shown to induce tumor regression in a minority of patients; however, no correlation has been observed between mutation status and clinical response. With the goal of identifying biomarkers of sensitivity to MEK inhibitor treatment, we performed an outlier analysis of a patient who experienced a complete, durable, and ongoing (> 5 years) response to selumetinib, a non-ATP competitive MEK inhibitor.

PATIENTS AND METHODS

Next-generation sequencing was used to analyze this patient's tumor as well as an additional 28 SB/LGS tumors. Functional characterization of an identified novel alteration of interest was performed.

RESULTS

Analysis of the extraordinary responder's tumor identified a 15-nucleotide deletion in the negative regulatory helix of the MAP2K1 gene encoding for MEK1. Functional characterization demonstrated that this mutant induced extracellular signal-regulated kinase pathway activation, promoted anchorage-independent growth and tumor formation in mice, and retained sensitivity to selumetinib. Analysis of additional LGS/SB tumors identified mutations predicted to induce extracellular signal-regulated kinase pathway activation in 82% (23 of 28), including two patients with BRAF fusions, one of whom achieved an ongoing complete response to MEK inhibitor-based combination therapy.

CONCLUSION

Alterations affecting the mitogen-activated protein kinase pathway are present in the majority of patients with LGS ovarian cancer. Next-generation sequencing analysis revealed deletions and fusions that are not detected by older sequencing approaches. These findings, coupled with the observation that a subset of patients with recurrent LGS ovarian cancer experienced dramatic and durable responses to MEK inhibitor therapy, support additional clinical studies of MEK inhibitors in this disease.

Abstract 3889: Genetic heterogeneity and distinct driver mutations in synchronous primary and metastatic breast cancers from therapy-naïve patients

Background: The metastatic process may constitute a biological bottleneck and may select for clones with genetic alterations that are distinct from those found in the dominant clone of the primary tumor. Here we sought to define whether the repertoires of somatic mutations found in biopsies of primary tumors would differ from those of their respective metastatic lesions in patients who did not receive any form of systemic therapy.

Methods: Flash frozen diagnostic biopsies from primary tumors and their distant metastases were obtained from 9 prospectively accrued treatment-naïve patients with stage IV breast cancer at presentation (3 estrogen receptor (ER)+/HER2+, 2 ER+/HER2-, 2 ER-/HER2+ and 2 ER-/HER2-). Metastatic lesions from the liver (5), bone (2), skin (1) or contra-lateral axillary lymph node (1) were biopsied. An additional formalin-fixed paraffin embedded (FFPE) biopsy of each primary tumor and metastasis, as well as plasma from 5 patients, were obtained. DNA from microdissected frozen samples and peripheral blood, as well as plasma from one patient, was subjected to high-depth whole exome sequencing and gene copy number profiling. DNA from all biopsies (frozen/FFPE) and plasma was subjected to targeted capture massively parallel sequencing for all single nucleotide variants (SNVs) and insertions and deletions (indels) found by exome sequencing and all exons of the 100 most frequently mutated genes in breast cancer. Driver mutations were defined by state-of-the-art bioinformatic methods and literature curation.

Results: In all cases, we detected founder genetic events in the modal population of primary tumors and their respective metastatic lesions (12-146 non-synonymous SNVs and 1-16 indels). Substantial genetic differences were observed between primary and their metastasis from these therapy-naïve patients, with a median of 9 non-synonymous mutations (range 0-42, median 9.6% of mutations) restricted to the primary tumor and not found in either biopsies of the metastases, and a median of 19 (range 1-73, median 20.2%) non-synonymous mutations restricted to the metastasis and not found in either biopsies of the primary tumors. The repertoire of mutations restricted to the metastatic lesions was unique to each case; however, we observed an enrichment of genes involved in the epithelial-to-mesenchymal transition (e.g. TCF7L2, SMAD4, KRIT1 and L1CAM). Plasma DNA analysis revealed that only 3.2%-38.3% of the mutations found in the primary tumor or its metastatic deposit could be detected in plasma.

Conclusions: Therapy-naïve primary breast cancers and their metastatic deposits differ in their repertoire of genetic alterations, even when two biopsies of each primary tumor and metastatic lesions are analyzed. The assessment of targetable genetic alterations in single biopsies from primary tumors may not be sufficient for the optimal selection of precision medicine-based therapies.

Citation Format: Charlotte K. Y. Ng, Francois-Clement Bidard, Salvatore Piscuoglio, Raymond S. Lim, Jean-Yves Pierga, Paul Cottu, Anne Vincent-Salomon, Agnes Viale, Larry Norton, Brigitte Sigal, Britta Weigelt, Jorge S. Reis-Filho. Genetic heterogeneity and distinct driver mutations in synchronous primary and metastatic breast cancers from therapy-naïve patients. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3889. doi:10.1158/1538-7445.AM2015-3889

Metastatic Competence Can Emerge with Selection of Preexisting Oncogenic Alleles without a Need of New Mutations

Several experimental models faithfully recapitulate many important facets of human metastatic disease. Here, we have performed whole-exome sequencing in five widely used experimental metastasis models that were independently derived through in vivo selection from heterogeneous human cancer cell lines. In addition to providing an important characterization of these model systems, our study examines the genetic evolution of metastatic phenotypes. We found that in vivo selected highly metastatic cell populations showed little genetic divergence from the corresponding parental population. However, selection of genetic variations that preexisted in parental populations, including the well-established oncogenic mutations KRAS(G13D) and BRAF(G464V), was associated with increased metastatic capability. Conversely, expression of the wild-type BRAF allele in metastatic cells inhibited metastatic outgrowth as well as tumor initiation in mice. Our findings establish that metastatic competence can arise from heterogeneous cancer cell populations without the need for acquisition of additional mutations and that such competence can benefit from further selection of tumor-initiating mutations that seed primary tumorigenesis.

CHZ868, a Type II JAK2 Inhibitor, Reverses Type I JAK Inhibitor Persistence and Demonstrates Efficacy in Myeloproliferative Neoplasms

Although clinically tested JAK inhibitors reduce splenomegaly and systemic symptoms, molecular responses are not observed in most myeloproliferative neoplasm (MPN) patients. We previously demonstrated that MPN cells become persistent to type I JAK inhibitors that bind the active conformation of JAK2. We investigated whether CHZ868, a type II JAK inhibitor, would demonstrate activity in JAK inhibitor persistent cells, murine MPN models, and MPN patient samples. JAK2 and MPL mutant cell lines were sensitive to CHZ868, including type I JAK inhibitor persistent cells. CHZ868 showed significant activity in murine MPN models and induced reductions in mutant allele burden not observed with type I JAK inhibitors. These data demonstrate that type II JAK inhibition is a viable therapeutic approach for MPN patients.