Pilot data suggest that duloxetine is effective in management of endocrine therapy-associated musculoskeletal pain, and a randomized placebo controlled trial of duloxetine has demonstrated efficacy for treatment of chemotherapy-induced neuropathic pain. In this mechanistic study of duloxetine versus placebo, we will investigate the change in pain sensitivity with treatment in order to evaluate both why duloxetine is effective for management of pain for some patients, as well as predictors of who is likely to benefit from duloxetine. A total of 84 women with early stage breast cancer who have chronic pain following treatment, as well as 48 women who are pain free, will be enrolled. All subjects will undergo assessment of pain sensitivity and complete questionnaires. Subjects with pain will be treated with duloxetine for a total of 7 weeks, with pain sensitivity assessments before treatment and after 4 weeks of full-dose treatment.