Introduction

Next to accidental causes, cancer accounts for the most frequent cause of childhood deaths with brain tumors being the most common cause of cancer related deaths in children. It is estimated that there are approximately 40,000 children living with the diagnosis of a tumor of the brain or spinal cord in the U.S. Surgical removal of brain tumors, irrespective of the tumor being benign or malignant, plays a very prominent role in successful therapy. However, some tumors, because of their infiltrative growth pattern or their location, are not amenable to surgical removal.

The treatment of these tumors has thus relied on the use of systemically delivered chemotherapy, either into the venous blood or orally. Both of these routes of administration are limited because of dose limiting toxicity, commonly causing injury to the bone marrow, liver and kidneys. Further, many chemotherapeutic agents are unable to be delivered to the site of the tumor growth because of the isolation of the brain from circulation, a phenomenon called the blood brain barrier (BBB). The inability to cross the BBB is particularly vexing with some newer and promising therapeutic agents due to their size or composition. Lastly, most cancer drugs are not specific for tumor cells and can affect any cell in the body, thus again resulting in toxicity to other organs.

The inability to surgically remove some infiltrative brain tumors
A natural barrier prohibiting some therapeutic agents from getting to the site of the brain tumor
The side effects or toxicity of systemic treatment
The lack of specificity of drugs used against tumor cells