<qa>  What will be determined by PET-FDG?Patients will have histologic confirmation of invasive breast cancer and will have a FDG-PET scan prior to axillary node assessment. All patients will have a sentinel node biopsy if any sentinel nodes can be located. Patients with a positive sentinel node will have an axillary node dissection. The results of the PET will be compared to the reference standard of histologic examination of all excised sentinel and non-sentinel axillary lymph nodes which will be referred to as axillary node assessment. Sensitivity, specificity, positive and negative predictive values for PET-FDG will be determined. 