One of the deadly properties of GBM is its capacity to diffusely infiltrate the surrounding normal brain tissue. Unlikely many malignancies, in GBM local disease progression, rather than metastatic disease, is the leading cause of death. Extent of resection plays a key role in the treatment of these patients with complete surgical resection improving outcome. In a prospective, non- interventional, multi-institutional study of over 140 patients with GBM and minimal or no residual tumor on post-operative MRI, Stummer et al.have shown that extent of resection is indeed associated with improved survival. However, despite evidence of complete resection on post-operative imaging studies, surgery is rarely truly complete. GBMs are invasive tumors and, at time of surgery, a clear boundary is not clearly identifiable, either on pre- or intra- operative imaging. Even when sophisticated imaging'techniques are used, they are unable to detect invasive brain cancer cell for proper pre-operative surgical planning to optimally delineate the tumor boundaries for a truly complete resection. Even if they were, brain eloquence would preclude a complete resection of most GBMs.

Despite extensive and complete surgical tumor removal coupled with radiation and chemotherapy, even in high doses, 90% of patients still fail at the border or within a few centimeters from the surgical cavity. Glioma cell migration outside the original tumor site may be responsible for this recurrence pattern. Cell migration is a complex, dynamic process and is well-documented in GBM. It involves, at least, 3 independent but coordinated biologic processes: 1) cell adhesion to components of the extracellular matrix, 2) cell's own motility and 3) invasion. Giese et al.) reported that cell migration is established by several independent mechanisms, facilitating the spread of tumor astrocytes, but with cell motility being the possible common denominator for this biologic behavior.

Invasion of tumor glioma cells is a multi-factorial process. To migrate, the cell needs a change in morphology and to interact with the extracellular matrix. It is possible that the surgical insult at the time of tumor removal may facilitate such an environment. Also, Wild-Bode et al.(6) have shown, in animal models, that sub-lethal doses of irradiation promote the migration and invasiveness of glioma cells. It is conceivable that the use of conventionally fractionated radiation therapy (2 Gy per day), even in doses above 60 Gy, leads to only sub-lethal damage potentially promoting cell migration.

In a recently completed Phase 2 study for patients with newly diagnosed GBM, our group has shown that the use of concurrent temozolomide and hypofractionated radiation therapy to a dose of 60 Gy given in 20 fractions (daily dose of 3 Gy) preceded by 2 weeks of temozolomide given in the post-operative setting was associated with 2-year survival rates of 63% and 29% for MGMT methylated and unmethylated tumors, respectively (Dr. G. Shenouda, personal information. Manuscript submitted for publication). These promising results may be possibly due to a dual effect of the use of neoadjuvant temozolomide (prior to radiation therapy) and the use of a hypofractionated radiotherapy regimen. The upfront use of temozolomide may have affected tumor control by interfering with the upstream signaling event triggered by the RT preventing cell migration and also by promoting inhibition of glioma cell invasion.

GBMs are one of the most rapidly growing tumors. Primary GBMs typically develop and grow to be greater than 3 cm in less than 4 months. Under the current standard treatment approach, patients undergo surgery and, rather than starting adjuvant therapy immediately at a moment when there is the least amount of residual tumor burden, they wait 3-4 weeks, for practical reasons, to start adjuvant treatment with RT and TMZ. In addition, the combined treatment takes an additional 6 weeks to complete. Thus it takes 9-10 weeks for patients to complete maximum local treatment. In other words, one of the most aggressive tumors has been given another 9-10 weeks to proliferate, repopulate and invade. It is conceivable that this delay in adjuvant treatment gives the residual brain cancer cells the opportunity to regrow and invade prior to completion of RT and TMZ thus contributing to 85% of all failures occurring at or within 2 cm of the original resection cavity margin.

The use of pre-operative RT, either alone or in combination with chemotherapy, has been successfully used in other pathologies. In patients with soft tissue sarcoma, localized . rectal cancer, locally advanced breast cancer, and esophageal cancer the use of pre-operative RT has been associated with improved local control (8-11). Recently, the use of neoadjuvant radiosurgery has been explored in patients harboring resectable metastatic brain lesions (12). A total of 47 patients underwent radiosurgery prior to the surgical procedure (total of 51 lesions) and the authors report high rates of local control with limited toxicity. The use of pre-operative RT has several theoretical advantages in patients with GBM. Neoadjuvant RT is delivered prior to the surgical procedure minimizing, theoretically, the risk of local cell migration at the time of the surgical intervention. It has also the advantage of treating a target that has an intact blood supply and, most importantly, RT will be delivered to a better defined target. It also allows a definitive portion of the treatment paradigm to be delivered in a timely manner with no prolonged delay.