Study to Evaluate a Preop Dose of Brivoligide Injection for Pain After Mastectomy in Patients With High PCS Scores

Inclusion Criteria: * Score of 16 or greater on the PCS scale * Scheduled to undergo unilateral or bilateral mastectomy with immediate tissue expander or implant placement * American Society of Anesthesiologists Physical Status Classification System ≤ 3 * Medically stable for this surgery with general anesthesia and intrathecal administration of study drug as determined by the Investigator * Body mass index of 18-45 kg/m2 * Have a stable medical regimen (for prescribed medications) for ≥ 7 days before randomization * Able to read and understand study instructions in English or Spanish, and willing and able to comply with all study procedures Exclusion Criteria: * Prior breast surgery in the index breast (either breast for bilateral surgery) in the last two years, other than biopsies and small/moderate volume lumpectomies * Induction chemotherapy or plans for adjunctive chemotherapy or any radiotherapy within 21 days of surgery * Known spinal deformities or cutaneous infection in the lumbar area that would preclude intrathecal administration of study drug * Planned use of liposomal formulated or long-acting local anesthetics, extended release opioid formulations (e.g., Oxycontin), long half-life opioids (e.g., methadone), or drugs with potential for adverse cognitive or memory effects (e.g., ketamine, scopolamine, or propranolol) preoperatively and/or at any time through the duration of the study * Use of more than 40 mg per day (on average) of oral morphine or its equivalent within 1 month prior to randomization * Current neurologic disorder, which could confound the assessment of pain * Unstable mental condition which would prevent the patient from understanding the nature and scope of the study and/or evidence of an uncooperative attitude in the opinion of the Investigator * Women who are pregnant or nursing * Participation in a clinical trial with the last dose or intervention within 1 month of randomization, or planned treatment in a clinical trial during this study * Previous participation in any study involving brivoligide injection