Breast cancer is the most common cancer in North American women. It is estimated that one in 8 American women will develop breast cancer during her lifetime. Surgical treatment has evolved from radical mastectomy to breast conservation, and systemic treatment has become increasingly important. The presence or absence of lymph node metastases is the most important prognostic factor used to determine type of systemic treatment necessary. Axillary dissection however, carries with it the risk of nerve injury, lymphedema, decreased arm motion and seroma formation. Clinical examination, ultrasound, CT scanning and MRI of the axilla are not sensitive or specific enough to eliminate the need for axillary dissection. Sentinel node biopsy (SNB) can predict the pathologic status of the axilla and theoretically could differentiate patients into those with positive node biopsies who require full dissection versus those who are negative and do not. Frozen section of the sentinel node is inaccurate and therefore SNB positive patients would require two surgical procedures. Positron Emission Tomography (PET) scanning of the axilla has been reported to have a high sensitivity and specificity and if used prior to surgery may guide the surgeon in determining the need for full axillary dissection versus SNB alone. PET scanning has also been reported to identify unsuspected distant metastases not found on standard staging examinations. This study will investigate the use of PET scanning in conjunction with SNB and results of both modalities will be correlated with histologic results of axillary dissection.