In the 1960s, American medical scientist Judah Folkman (1933–2008) realized that malignant tumors could not grow without nourishment, which is delivered by the blood. Rapidly growing tumors actually cause the formation of new blood vessels in a process known as angiogenesis. Folkman’s hypothesis was that by identifying the substances used to cause angiogenesis, drugs could be formulated to prevent new vessel formation, thus starving the tumors. This work has led to the identification of at least two substances that inhibit angiogenesis: endostatin and angiostatin. These drugs are still being studied as of this writing and hold promise as new therapies to combat aggressive tumors.