SUMMARY Sonic hedgehog (Shh), a soluble ligand overexpres sed by neoplastic cells in pancreatic ductal adenocarcinoma (PDAC), drives formation of a fibroblast-rich desmoplastic stroma. To better understand its role in malignant progression, we deleted Shh in a well-defined mouse model of PDAC. As predicted, Shh-deficient tumors had reduced stromal content. Surprisingly, such tumors were more aggressive and exhibited undifferentiated histology, increased vascularity, and heightened proliferation – features that were fully recapitulated in control mice treated with a Smoothened inhibitor. Furthermore, administration of VEGFR blocking antibody selectively improved survival of Shh-deficient tumors, indicating that Hedgehog-driven stroma suppresses tumor growth in part by restraining tumor angiogenesis. Together, these data demonstrate that some components of the tumor stroma can act to restrain tumor growth.

Poorly differentiated neuroendocrine carcinomas (NEC) of the pancreas are rare malignant neoplasms with a poor prognosis. The aim of this study was to determine the clinicopathologic and genetic features of poorly differentiated NECs and compare them to other types of pancreatic neoplasms. We investigated alterations of KRAS, CDKN2A/p16, TP53, SMAD4/DPC4, DAXX, ATRX, PTEN, Bcl2 and RB1 by immunohistochemistry and/or targeted exomic sequencing in surgically resected specimens of nine small cell NEC, 10 large cell NECs and 11 well-differentiated neuroendocrine tumors (PanNETs) of the pancreas. Abnormal immunolabeling patterns of p53 and Rb were frequent (p53, 18 of 19, 95%; Rb, 14 of 19, 74%) in both small cell and large cell NEC, whereas Smad4/Dpc4, DAXX and ATRX labeling were intact in virtually all of these same carcinomas. Abnormal immunolabeling of p53 and Rb proteins correlated with intragenic mutations in the TP53 and RB1 genes. By contrast, DAXX and ATRX was lost in 45% of PanNETs whereas p53 and Rb immunolabeling was intact in these same cases. Overexpression of Bcl-2 protein was observed in all nine small cell NECs (100%) and in five of 10 (50%) large cell NECs compared to only two of 11 (18%) PanNETs. Bcl-2 overexpression was significantly correlated with higher mitotic rate and Ki-67 labeling index in neoplasms in which it was present. Small cell NECs are genetically similar to large cell NECs, and these genetic changes are distinct from those reported in PanNETs. The finding of Bcl-2 overexpression in poorly differentiated NECs, particularly small cell NEC, suggests that Bcl-2 antagonists/inhibitors may be a viable treatment option for these patients.

During the evolutionary progression of pancreatic ductal adenocarcinoma (PDAC), heterogeneous subclonal populations emerge that drive primary tumor growth, regional spread, distant metastasis, and patient death1–3. However, the genetics of metastases largely reflects that of the primary tumor in untreated patients, and PDAC driver mutations are shared by all subclones1. This raises the possibility than an epigenetic process might operate during metastasis. Here we detected striking epigenetic reprogramming of global chromatin modifications during the natural evolutionary history of distant metastasis. Genome-wide mapping revealed that global changes were targeted to thousands of large chromatin domains across the genome that collectively specified malignant traits, including euchromatin and large organized chromatin K9-modified (LOCK) heterochromatin. Remarkably, distant metastases co-evolved a dependence on the oxidative branch of the pentose phosphate pathway (oxPPP), and oxPPP inhibition selectively reversed malignant chromatin and expression states and blocked tumorigenicity. This suggests a model whereby linked metabolic-epigenetic programs are selected for enhanced tumorigenic fitness during the evolution of distant metastasis.

Purpose Genetic alterations of KRAS, CDKN2A, TP53 and SMAD4 are the most frequent events in pancreatic cancer. We determined the extent to which these four alterations are coexistent in the same carcinoma, and their impact on patient outcome. Experimental Design Pancreatic cancer patients who underwent an autopsy were studied (n=79). Matched primary and metastasis tissues were evaluated for intragenic mutations in KRAS, CDKN2A and TP53 and immunolabeled for CDKN2A, TP53 and SMAD4 protein products. The number of altered driver genes in each carcinoma was correlated to clinicopathologic features. Kaplan-Meier estimates were used to determine median disease free and overall survival, and a Cox proportional hazards model used to compare risk factors. Results The number of genetically altered driver genes in a carcinoma was variable, with only 29 patients (37%) having an alteration in all four genes analyzed. The number of altered driver genes was significantly correlated with disease free survival (p=0.008), overall survival (p=0.041) and metastatic burden at autopsy (p=0.002). On multivariate analysis, the number of driver gene alterations in a pancreatic carcinoma remained independently associated with overall survival (p=0.046). Carcinomas with only one to two driver alterations were enriched for those patients with the longest survival (median 23 months, range 1–53). Conclusions Determinations of the status of the four major driver genes in pancreatic cancer, and specifically the extent to which they are coexistent in an individual patients cancer, provides distinct information regarding disease progression and survival that is independent of clinical stage and treatment status.

Objective We assessed circulating tumor cells (CTCs) with epithelial and mesenchymal phenotypes as a potential prognostic biomarker for patients with pancreatic adenocarcinoma (PDAC). Background PDAC is the fourth leading cause of cancer death in the United States. There is an urgent need to develop biomarkers that predict patient prognosis and allow for better treatment stratification. Methods Peripheral and portal blood samples were obtained from 50 patients with PDAC before surgical resection and filtered using the Isolation by Size of Epithelial Tumor cells method. CTCs were identified by immunofluorescence using commercially available antibodies to cytokeratin, vimentin, and CD45. Results Thirty-nine patients (78%) had epithelial CTCs that expressed cytokeratin but not CD45. Twenty-six (67%) of the 39 patients had CTCs which also expressed vimentin, a mesenchymal marker. No patients had cytokeratin-negative and vimentin-positive CTCs. The presence of cytokeratin-positive CTCs (P < 0.01), but not mesenchymal-like CTCs (P = 0.39), was associated with poorer survival. The presence of cytokeratin-positive CTCs remained a significant independent predictor of survival by multi-variable analysis after accounting for other prognostic factors (P < 0.01). The detection of CTCs expressing both vimentin and cytokeratin was predictive of recurrence (P = 0.01). Among patients with cancer recurrence, those with vimentin-positive and cytokeratin-expressing CTCs had decreased median time to recurrence compared with patients without CTCs (P = 0.02). Conclusions CTCs are an exciting potential strategy for understanding the biology of metastases, and provide prognostic utility for PDAC patients. CTCs exist as heterogeneous populations, and assessment should include phenotypic identification tailored to characterize cells based on epithelial and mesenchymal markers.