Abstract and Introduction
Pancreatic ductal adenocarcinoma continues to be one of the most difficult diseases to manage with one of the highest cancer mortality rates. This is due to several factors including nonspecific symptomatology and subsequent diagnosis at an advanced stage, aggressive metastatic behavior that is incompletely understood, and limited response to current therapeutic regimens. As in other cancers, there is great interest in studying the role of the tumor microenvironment in pancreatic ductal adenocarcinoma and whether components of this environment could serve as research and therapeutic targets. In particular, attention has turned toward the desmoplastic collagen-rich pancreatic ductal adenocarcinoma stroma for both biological and clinical insight. In this study, we used quantitative second harmonic generation microscopy to investigate stromal collagen organization and structure in human pancreatic ductal adenocarcinoma pathology tissues compared with non-neoplastic tissues. Collagen topology was characterized in whole-tissue microarray cores and at specific pathology-annotated epithelial–stroma interfaces representing 241 and 117 patients, respectively. We quantitatively demonstrate that a unique collagen topology exists in the periductal pancreatic ductal adenocarcinoma stroma. Specifically, collagen around malignant ducts shows increased alignment, length, and width compared with normal ducts and benign ducts in a chronic pancreatitis background. These findings indicate that second harmonic generation imaging can provide quantitative information about fibrosis that complements traditional histopathologic insights and can serve as a rich field for investigation into pathogenic and clinical implications of reorganized collagen as a pancreatic ductal adenocarcinoma disease marker.
Pancreatic ductal adenocarcinoma is one of the most devastating human malignancies. It is currently the fourth leading cause of cancer death and projects to become the second leading cause by 2030. The 5-year relative survival rate has remained in the single digits for decades. Pancreatic ductal adenocarcinoma is notoriously difficult to detect before an advanced, inoperable stage is reached due to nonspecific symptomatology and the retroperitoneal location of the pancreas, which makes palpation or routine biopsy of suspicious masses difficult. Recent advances in the sensitivity and specificity of preoperative imaging modalities such as computer tomography, magnetic resonance imaging, positron emission tomography, endoscopic ultrasonography, and endoscopic retrograde cholangiopancreatography have played an important role in enhancing pancreatic ductal adenocarcinoma diagnosis, detailing the relationship of lesions to nearby anatomical structures, and determining the course of management. Despite these advances, only 10–15% of patients are diagnosed at a localized disease stage when surgical resection is possible as a potential curative therapy. However, postsurgical recurrence rates are high with 5-year survival rate of only 10%, and the disease has a notable resistance to adjuvant therapeutic strategies.
New insights into pancreatic ductal adenocarcinoma pathogenesis are critically needed to enhance clinical management and inform novel therapeutic targets. Pancreatic ductal adenocarcinoma tumors are characterized by an extensively desmoplastic stroma when examined histologically. This dense fibrosis can account for up to 90% of the overall tumor volume. In a number of different cancer types, stromal properties have demonstrated importance in disease identification, progression, and patient prognosis.[5–12] Given the pronounced desmoplastic reaction in pancreatic ductal adenocarcinoma, a large number of recent research efforts have focused on elucidating stroma–cancer interactions for both nuanced insight into disease progression and for potential diagnostic, prognostic, or therapeutic targets.
The dominant extracellular matrix component of most tumor stromas, including that of pancreatic ductal adenocarcinoma, is fibrillar collagen. Recent technological advances in nonlinear microscopy modalities such as second harmonic generation imaging have enabled visualization of collagen-based changes at cellular resolution and provided unprecedented insight into tumor growth and metastasis. Fibrillar collagens possess a unique non-centrosymmetric structure allowing them to act as a frequency doubler when interacting with multiphoton laser light. This coherent, nonabsorptive light interaction process can be exploited to obtain high-resolution, quantifiable images of discrete collagen fibers in a number of sources including two-dimensional histopathology specimens, three-dimensional intact tissues, and live animal models without the need for exogenous staining. Using second harmonic generation imaging, a number of groups have shown that changes in collagen fiber structure and organization during tumor initiation and progression have biological consequences and correlate with clinical outcomes in a number of other solid tumor types.[19–21]
Although increased stromal collagen content has long been clinically documented in pancreatic ductal adenocarcinoma cases, its specific topology in relationship to the malignant glands has yet to be investigated in human tissue specimens. In this study, we utilized second harmonic generation imaging to interrogate and quantify collagen changes in relation to histologic features within pancreatic carcinomas. We demonstrate that a characteristic collagen topology exists in the stroma at the interface with malignant epithelium, and that specific collagen attributes provide quantitative parameters for distinguishing pancreatic ductal adenocarcinoma tissue from benign tissue, including both normal ducts and ducts in chronic pancreatitis. These findings validate a methodology and establish an important foundation to further decipher the biological and clinical implications of collagen topology as a pancreatic ductal adenocarcinoma disease marker.
Mod Pathol. 2015;28(11):1470-1480. © 2015 Nature Publishing Group