The formation of vascular stroma (angiogenesis) is essential for tumor growth and may also influence invasion and metastasis. Quantitation of angiogenesis may serve as a prognostic marker in certain malignancies and novel therapies targeted at inhibiting angiogenesis may prove to play an important role in control of tumor growth.

In situ hybridization (ISH) studies have helped to define some of the molecular and cellular events responsible for the formation of vascular stroma in malignancy.

Vascular permeability factor (VPF), also known as vascular endothelial growth factor (VEGF), is a multifunctional cytokine associated with tumor angiogenesis. Vascular endothelial cells express at least two tyrosine kinase receptors for VPF, flt-1 and KDR. VPF acts as an angiogenic factor in several ways. It is an endothelial cell growth factor, alters endothelial cell gene expression, induces endothelial cell migration, and it is also a potent inducer of microvascular hyperpermeability (50,000 times as strong as histamine).