The objectives of this assessment were to evaluate the diagnostic accuracy, cost-effectiveness and effect on patient outcomes of positron emission tomography (PET), with or without computed tomography (CT), and magnetic resonance imaging (MRI) in the evaluation of axillary lymph node metastases in patients with newly diagnosed early-stage breast cancer. PET and MRI are assessed firstly as a replacement for SLNB or 4-NS, and secondly as an additional test prior to SLNB or 4-NS.