Mechanistic Study of Duloxetine in Breast Cancer Patients With Chronic Pain

Early stage breast cancer is typically treated with surgery, chemotherapy, radiation therapy, and/or endocrine therapy. Following treatment, 25-60% of breast cancer survivors have reported chronic pain, which can be difficult to manage. Duloxetine is a serotonin norepinephrine reuptake inhibitor that is FDA approved for treatment of depression, anxiety, fibromyalgia, diabetic neuropathic pain, knee arthritis, and low back pain. Data from a randomized, placebo-controlled clinical trial of duloxetine demonstrated that it is effective in management of both aromatase inhibitor-associated musculoskeletal pain and chemotherapy-induced neuropathic pain. In this mechanistic study, we investigated 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. The original protocol was designed as a randomized, placebo-controlled cross-over trial, with planned enrollment of 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. However because of challenges with logistics of the protocol and pain testing, the trial was redesigned after only 7 patients with pain were enrolled. The new design was a single arm trial, and all patients with pain were treated with duloxetine (no placebo); there was still a non-treatment comparator arm of patients without pain. Patients were enrolled first at the University of Michigan and then the University of Utah. A total of 39 patients with pain and 43 controls without pain were enrolled before the trial closed to enrollment. All subjects underwent assessment of pain sensitivity and completed questionnaires. Subjects with pain were treated with duloxetine for a total of 7 weeks, with pain sensitivity assessments before treatment and after 4 weeks of full-dose treatment. The data from the control patients (who did not receive any study medication) are being compared to those from the patients with pain to understand more about the differences between patients who do and do not experience treatment-related pain, and to interpret the post-intervention patient-reported and pain assessment results.