Development of solid tumors, tumor progression, and spread depend on the complex interplay of tumor cells and cells of the tumor microenvironment. Intercellular signals such as cell-cell or cell-matrix contacts, growth factors, chemokines and cytokines stir and orchestrate tumor cell fate and the course of the disease. Within the tumor microenvironment fibroblasts represent a highly active cellular as well as heterogeneous cell population. These cancer-associated fibroblasts (CAFs) have been shown to play a central role, since they secrete an array of factors that affect tumor and tumor-associated cells. Although CAFs have mainly been regarded as tumor-promoting cells, several groups have shown that fibroblasts are not only phenotypically heterogeneous in different tumor types, but are also functionally distinct within one tumor entity or even within the same patient. In pancreatic ductal adenocarcinoma for example, a tumor-restraining CAF subpopulation has been described.

In order to broaden our understanding of the fibroblast heterogeneity and how fibroblasts can affect tumor growth and progression, in vitro assays represent valuable tools to further study these cells in detail. Thus, the aim of this collection is to provide examples of how to isolate fibroblasts from primary tissues, share optimized protocols for primary cultivation and introduce protocols for downstream assays such as co-cultivation, immunofluorescence or analysis of secreted factors.