Tumour-stroma interactions in pancreatic ductal adenocarcinoma: rationale and current evidence for new therapeutic strategies.

Most patients with pancreatic cancer present with advanced/metastatic disease and have a dismal prognosis. Despite the proven albeit modest benefits of gemcitabine demonstrated over a decade ago, subsequent advances have been slow, suggesting it may be time to take a different approach. It is thought that some key characteristics of pancreatic cancer, such as the desmoplasia, restricted vasculature and hypoxic environment, may prevent the delivery of chemotherapy to the tumour thereby explaining the limited benefits observed to-date. Moreover, there is evidence to suggest that the stroma is not only a mechanical barrier but also constitutes a dynamic compartment of pancreatic tumours that is critically involved in tumour formation, progression and metastasis. Thus, targeting the stroma and the tumour represents a promising therapeutic strategy. Currently, several stroma-targeting agents are entering clinical development. Among these, nab-paclitaxel appears promising since it combines cytotoxic therapy with targeted delivery via its proposed ability to bind SPARC on tumour and stromal cells. Preclinical data indicate that co-treatment with nab-paclitaxel and gemcitabine results in stromal depletion, increased tumour vascularization and intratumoural gemcitabine concentration, and increased tumour regression compared with either agent alone. Phase I/II study data also suggest that a high level of antitumor activity can be achieved with this combination in pancreatic cancer. This was recently confirmed in a Phase III study which showed that nab-paclitaxel plus gemcitabine significantly improved overall survival (HR 0.72) and progression-free survival (HR 0.69) versus gemcitabine alone for the first-line treatment of patients with metastatic pancreatic cancer.