The main function of fibroblasts is to maintain the structural integrity of connective tissues by continuously secreting precursors of the extracellular matrix. Like other cells of connective tissue, fibroblasts are derived from primitive mesenchyme. Thus they express the intermediate filament protein vimentin, a feature used as a marker to distinguish their mesodermal origin. In addition forming and maintaining extracellular matrices, they also regulate interstitial fluid volume and pressure, and wound healing. Many diseases are associated with dysregulation of the injury repair response and fibroblast function, leading to increased or decreased deposition of extracellular matrix proteins, altered tissue architecture, impaired function and in some cases significant morbidity and mortality. This includes association with cancer cells at all stages of cancer progression.