Role of angiogenesis in drug resistance.

Tumor angiogenesis seems to be an important factor in determining therapeutic effectiveness and patient prognosis. An abundance of data on tumor angiogenesis is available and it clearly shows that most human solid tumors are heterogeneously vascularized and oxygenated and contain hypoxic regions. Such regions and areas of reduced vascularization can affect the response to a variety of drugs. Direct measurements of angiogenesis in various types of tumors have, upon correlation of the data with therapeutic outcome, shown that a high vascular density is associated with a decreased response to therapy and short overall survival time. Therefore, the extent of tumor angiogenesis may well be an important factor contributing to the difficulty of successful therapy in certain tumor types.