Genetic analyses of isolated high-grade pancreatic intraepithelial neoplasia (HG-PanIN) reveal paucity of alterations in TP53 and SMAD4

New Developments in the Molecular Mechanisms of Pancreatic Tumorigenesis

Pancreatic cancer is an aggressive disease with a dismal prognosis in dire need of novel diagnostic and therapeutic approaches. The past decade has witnessed an explosion of data on the genetic alterations that occur in pancreatic cancer, as comprehensive next-generation sequencing analyses have been performed on samples from large cohorts of patients. These studies have defined the genomic landscape of this disease and identified novel candidates whose mutations contribute to pancreatic tumorigenesis. They have also clarified the genetic alterations that underlie multistep tumorigenesis in precursor lesions and provided insights into clonal evolution in pancreatic neoplasia. In addition to these important insights into pancreatic cancer biology, these large scale genomic studies have also provided a foundation for the development of novel early detection strategies and targeted therapies. In this review, we discuss the results of these comprehensive sequencing studies of pancreatic neoplasms, with a particular focus on how their results will impact the clinical care of patients with pancreatic cancer.

Mutant p53R270H drives altered metabolism and increased invasion in pancreatic ductal adenocarcinoma

Pancreatic cancer is characterized by nearly universal activating mutations in KRAS. Among other somatic mutations, TP53 is mutated in more than 75% of human pancreatic tumors. Genetically engineered mice have proven instrumental in studies of the contribution of individual genes to carcinogenesis. Oncogenic Kras mutations occur early during pancreatic carcinogenesis and are considered an initiating event. In contrast, mutations in p53 occur later during tumor progression. In our model, we recapitulated the order of mutations of the human disease, with p53 mutation following expression of oncogenic Kras. Further, using an inducible and reversible expression allele for mutant p53, we inactivated its expression at different stages of carcinogenesis. Notably, the function of mutant p53 changes at different stages of carcinogenesis. Our work establishes a requirement for mutant p53 for the formation and maintenance of pancreatic cancer precursor lesions. In tumors, mutant p53 becomes dispensable for growth. However, it maintains the altered metabolism that characterizes pancreatic cancer and mediates its malignant potential. Further, mutant p53 promotes epithelial-mesenchymal transition (EMT) and cancer cell invasion. This work generates new mouse models that mimic human pancreatic cancer and expands our understanding of the role of p53 mutation, common in the majority of human malignancies.

Pancreatic Juice Mutation Concentrations Can Help Predict the Grade of Dysplasia in Patients Undergoing Pancreatic Surveillance

Purpose: The measurement of mutations in pancreatic juice samples collected from the duodenum during endoscopic ultrasound (EUS) may improve the diagnostic evaluation of patients undergoing pancreatic surveillance. Our aim was to evaluate the accuracy of using pancreatic juice mutation concentrations to predict the presence and histologic grade of neoplasia in the pancreas.Experimental Design: Digital next-generation sequencing (NGS) of pancreatic juice DNA using a targeted 12-gene panel was performed on 67 patients undergoing pancreatic evaluation during EUS, including patients with pancreatic ductal adenocarcinoma, patients who subsequently underwent pancreatic resection for precursor lesions, patients undergoing surveillance for their familial/inherited susceptibility to pancreatic cancer, and normal pancreas disease controls.Results: Patients with pancreatic cancer or high-grade dysplasia as their highest grade lesion had significantly higher pancreatic juice mutation concentrations than all other subjects (mean/SD digital NGS score; 46.6 ± 69.7 vs. 6.2 ± 11.6, P = 0.02). Pancreatic juice mutation concentrations distinguished patients with pancreatic cancer or high-grade dysplasia in their resection specimen from all other subjects with 72.2% sensitivity and 89.4% specificity [area under the curve (AUC) = 0.872]. Mutant TP53/SMAD4 concentrations could distinguish patients with pancreatic cancer or high-grade dysplasia in their resection specimen from all other subjects with 61.1% sensitivity and 95.7% specificity (AUC = 0.819). Among 31 high-risk individuals under surveillance, 2 of the 3 individuals with most abnormal pancreatic juice mutation profiles also had the most abnormalities on pancreatic imaging.Conclusions: Pancreatic juice mutation analysis using digital NGS has potential diagnostic utility in the evaluation of patients undergoing pancreatic surveillance. Clin Cancer Res; 24(12); 2963-74. ©2018 AACRSee related commentary by Lipner and Yeh, p. 2713.

A genetic roadmap of pancreatic cancer: still evolving

A diagnosis of pancreatic ductal adenocarcinoma (PDA) is often fatal. PDA is widely recognised as one of the 'incurable cancers' because therapies against this tumour type are generally ineffective. The fatal nature of this tumour is due to its aggressive clinical course. Pancreatic cancer commonly presents at the metastatic stage; even in cases where tumours are localised to the pancreas at diagnosis, metastatic seeds have often been invariably been spawned off, frustrating surgical attempts to cure the cancer. The key principles of pancreatic cancer mutational development were outlined nearly two decades ago using the genetics of precursor lesions to position the various stages of tumour progression. Since then, there has been a cavalcade of new data. How these recent studies impact the classical perceptions of pancreatic cancer development is a work in progress. Given that significant improvements in patient outcomes are not in sight for this disease, it is likely that broadening the current perspectives and acquiring deeper biological insights into the morphogenetic route of tumour development will be needed to foster new strategies for more effective cancer control.

Pancreatic Cancer: Molecular Characterization, Clonal Evolution and Cancer Stem Cells

Pancreatic Ductal Adenocarcinoma (PDAC) is the fourth most common cause of cancer-related death and is the most lethal of common malignancies with a five-year survival rate of <10%. PDAC arises from different types of non-invasive precursor lesions: intraductal papillary mucinous neoplasms, mucinous cystic neoplasms and pancreatic intraepithelial neoplasia. The genetic landscape of PDAC is characterized by the presence of four frequently-mutated genes: KRAS, CDKN2A, TP53 and SMAD4. The development of mouse models of PDAC has greatly contributed to the understanding of the molecular and cellular mechanisms through which driver genes contribute to pancreatic cancer development. Particularly, oncogenic KRAS-driven genetically-engineered mouse models that phenotypically and genetically recapitulate human pancreatic cancer have clarified the mechanisms through which various mutated genes act in neoplasia induction and progression and have led to identifying the possible cellular origin of these neoplasias. Patient-derived xenografts are increasingly used for preclinical studies and for the development of personalized medicine strategies. The studies of the purification and characterization of pancreatic cancer stem cells have suggested that a minority cell population is responsible for initiation and maintenance of pancreatic adenocarcinomas. The study of these cells could contribute to the identification and clinical development of more efficacious drug treatments.

Pancreatic undifferentiated carcinoma with osteoclast-like giant cells is genetically similar to, but clinically distinct from, conventional ductal adenocarcinoma

Undifferentiated carcinoma of the pancreas with osteoclast-like giant cells (UCOGC) is currently considered a morphologically and clinically distinct variant of pancreatic ductal adenocarcinoma (PDAC). In this study, we report clinical and pathological features of a series of 22 UCOGCs, including the whole exome sequencing of eight UCOGCs. We observed that 60% of the UCOGCs contained a well-defined epithelial component and that patients with pure UCOGC had a significantly better prognosis than did those with an UCOGC with an associated epithelial neoplasm. The genetic alterations in UCOGC are strikingly similar to those known to drive conventional PDAC, including activating mutations in the oncogene KRAS and inactivating mutations in the tumor suppressor genes CDKN2A, TP53, and SMAD4. These results further support the classification of UCOGC as a PDAC variant and suggest that somatic mutations are not the determinants of the unique phenotype of UCOGC. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

IL2RG, identified as overexpressed by RNA-seq profiling of pancreatic intraepithelial neoplasia, mediates pancreatic cancer growth

Pancreatic ductal adenocarcinoma evolves from precursor lesions, the most common of which is pancreatic intraepithelial neoplasia (PanIN). We performed RNA-sequencing analysis of laser capture microdissected PanINs and normal pancreatic duct cells to identify differentially expressed genes between PanINs and normal pancreatic duct, and between low-grade and high-grade PanINs. One of the most highly overexpressed transcripts identified in PanIN is interleukin-2 receptor subunit gamma (IL2RG) encoding the common gamma chain, IL2Rγ. CRISPR-mediated knockout of IL2RG in orthotopically implanted pancreatic cancer cells resulted in attenuated tumor growth in mice and reduced JAK3 expression in orthotopic tumors. These results indicate that IL2Rγ/JAK3 signaling contributes to pancreatic cancer cell growth in vivo.

Precancer Atlas to Drive Precision Prevention Trials

Cancer development is a complex process driven by inherited and acquired molecular and cellular alterations. Prevention is the holy grail of cancer elimination, but making this a reality will take a fundamental rethinking and deep understanding of premalignant biology. In this Perspective, we propose a national concerted effort to create a Precancer Atlas (PCA), integrating multi-omics and immunity - basic tenets of the neoplastic process. The biology of neoplasia caused by germline mutations has led to paradigm-changing precision prevention efforts, including: tumor testing for mismatch repair (MMR) deficiency in Lynch syndrome establishing a new paradigm, combinatorial chemoprevention efficacy in familial adenomatous polyposis (FAP), signal of benefit from imaging-based early detection research in high-germline risk for pancreatic neoplasia, elucidating early ontogeny in BRCA1-mutation carriers leading to an international breast cancer prevention trial, and insights into the intricate germline-somatic-immunity interaction landscape. Emerging genetic and pharmacologic (metformin) disruption of mitochondrial (mt) respiration increased autophagy to prevent cancer in a Li-Fraumeni mouse model (biology reproduced in clinical pilot) and revealed profound influences of subtle changes in mt DNA background variation on obesity, aging, and cancer risk. The elaborate communication between the immune system and neoplasia includes an increasingly complex cellular microenvironment and dynamic interactions between host genetics, environmental factors, and microbes in shaping the immune response. Cancer vaccines are in early murine and clinical precancer studies, building on the recent successes of immunotherapy and HPV vaccine immune prevention. Molecular monitoring in Barrett's esophagus to avoid overdiagnosis/treatment highlights an important PCA theme. Next generation sequencing (NGS) discovered age-related clonal hematopoiesis of indeterminate potential (CHIP). Ultra-deep NGS reports over the past year have redefined the premalignant landscape remarkably identifying tiny clones in the blood of up to 95% of women in their 50s, suggesting that potentially premalignant clones are ubiquitous. Similar data from eyelid skin and peritoneal and uterine lavage fluid provide unprecedented opportunities to dissect the earliest phases of stem/progenitor clonal (and microenvironment) evolution/diversity with new single-cell and liquid biopsy technologies. Cancer mutational signatures reflect exogenous or endogenous processes imprinted over time in precursors. Accelerating the prevention of cancer will require a large-scale, longitudinal effort, leveraging diverse disciplines (from genetics, biochemistry, and immunology to mathematics, computational biology, and engineering), initiatives, technologies, and models in developing an integrated multi-omics and immunity PCA - an immense national resource to interrogate, target, and intercept events that drive oncogenesis. Cancer Res; 77(7); 1510-41. ©2017 AACR.