Stromal responses to carcinomas of the pancreas: Juxtatumoral gene expression conforms to the infiltrating pattern and not the biologic subtype

Abstract

If there is a “science” of tumor-stromal interactions, there must be a set of biologic rules that are organ-site dependent. One way to explore this hypothesis would be to compare the patterns of gene expression of two biologically distinct neoplasms that arise within the same organ site. Using non-radioactive in situ hybridization, we evaluated the gene expression patterns of three genes previously shown to be robust markers of the juxtatumoral stroma within eight infiltrating ductal adenocarcinoma of the pancreas (ApoC1, ApoD and MMP11), and compared these patterns to those associated with seven infiltrating colloid and tubular carcinomas arising in association with intraductal papillary mucinous neoplasms (IPMNs), a histologically distinct form of primary carcinoma of the pancreas, two surgically resected samples of chronic pancreatitis and two surgically resected pancreatic cancer liver metastases. Robust juxtatumoral stromal expression was noted for all three markers within all eight conventional infiltrating ductal adenocarcinoma tissues, but not in samples of chronic pancreatitis. Among the carcinomas arising within an IPMN, expression for all three markers was also noted for five of seven infiltrating carcinomas analyzed. However, when labeling for these three markers was analyzed with respect to infiltrative growth pattern, positive labeling was only seen in areas of tubular (ductal-type) growth and not in areas of colloid carcinoma. This observation was further supported by two infiltrating carcinomas arising in an IPMN that showed both tubular and colloid growth patterns within the same neoplasm indicating the host stromal response observed may relate to infiltrative growth pattern rather than the biology of the primary tumor type. Moreover, these robust patterns within conventional infiltrating ductal adenocarcinomas were not retained within matched metastases to the liver, indicating the importance of the tumor microenvironment in the host stromal response. Juxtatumoral stroma was found to be composed of a least two cell types, tumor-infiltrating macrophages and fibroblasts, highlighting the complexity of tumor-stromal interactions within an infiltrating carcinoma. Since the juxtatumoral gene expression response is the strongest indication of direct communication between stroma and cancer cells, we provide evidence of a stereotypical response to infiltrative growth that might predominate in tumor-stromal interactions independent of cancer type, a finding with clinical implications for therapeutic modalities that target this response in human tumors.