patients will undergo an pre-treatment and on-treatment tumor biopsy, to measure VEGF expression, and identify the time point of induction of VEGF expression.

These patients will receive bevacizumab once a week during their chemoradiation, starting at the identified time point of enhanced VEGF expression. These patients will also undergo and pre-treatment tumor biopsy and 1 tumor biopsy 1 week after the start of bevacizumab treatment.

patients will receive bevacizumab (3mg/kg/wk) starting from the identified induction time point of VEGF expression

To compare the VEGF mRNA expression in the pre-treatment and on-treatment tumor biopsies, to measure the change in VEGF expression from baseline.

To determine the level of pVEGFR2 expression in tumor biopsies of patients that received bevacizumab, and to compare that to their pre-treatment expression levels, to identify the changes in expression from baseline.

To identify the expression of other pro-angiogenic factors in the tumor, and to measure the changes from baseline expression (pre-treatment vs on-treatment biopsies).