Chronic pain occurs in 35-68% of patients after breast cancer surgery (mastectomy), is associated with psychological distress, physical and psychosocial disability, and long-term use of opioid medications. We will examine genetic expression (RNA-sequencing) of nerves from the breast of patients undergoing mastectomy to identify molecular mechanisms associated with the development of chronic pain after surgery. Based entirely on human research, the proposed investigation can fundamentally advance our understanding of why patients develop neuropathic pain after breast surgery and identify molecular targets of future, effective therapeutics.