Inclusion Criteria:

- Female;

- Histologically proven stage 0-III invasive carcinoma of the breast that is ER and/or
PR positive by immunohistochemical staining, who are receiving a standard dose of
aromatase inhibitor (AI) therapy (letrozole 2.5mg once daily or exemestane 25mg once
daily or anastrozole 1mg once daily). Women with oligometastatic disease may be
included at the discretion of the principal investigator. Surgical resection,
chemotherapy, and radiation therapy must have been completed at the time of study
enrollment, with the exception of trastuzumab;

- AI therapy has been ongoing for ≥ 2 weeks and treatment is expected to continue;

- AI-associated musculoskeletal symptoms, defined as:

- Grade 1 or higher musculoskeletal pain that developed or worsened (6 or 7 on
CGICS) during AI therapy or

- Grade 1 or higher sensory neuropathy that developed or worsened (6 or 7 on
CGICS) during AI therapy;

- Average pain of ≥4 on the 11-point Likert scale of question #5 of the Brief Pain
Inventory;

- ECOG performance status 0-2;

- Willing and able to sign an informed consent document.

Exclusion Criteria:

- Known hypersensitivity to duloxetine or any of the inactive ingredients;

- New musculoskeletal pain that is due specifically to fracture or traumatic injury;

- Treatment with monoamine oxidase inhibitors (MAO-I) within 14 days of enrollment;

- Concurrent treatment with phenothiazines (including thioridazine), propafenone,
flecainide, triptans, MAO-Is, SSRIs, SNRIs, or tricyclic antidepressants;

- Currently primary psychiatric diagnosis (schizophrenia, psychosis) or suicidal
ideation, history of bipolar disorder, or seizure disorder;

- Chronic liver disease, end stage renal disease, or creatinine clearance < 30 mL/min
as defined by the Cockroft-Gault equation;

- Uncontrolled narrow-angle glaucoma or clinically significant coagulation disorder;

- Pregnant or breast feeding;

- History of alcohol or other substance abuse or dependence within the year prior to
enrollment;

- Serious or unstable medical condition that could likely lead to hospitalization
during the course of the study or compromise study participation.