Vitamin B12 for the Treatment of Aromatase Inhibitors Associated Musculoskeletal Symptoms in Patients with Stage I-III Breast Cancer

Inclusion Criteria

• Must have histologically or cytologically confirmed estrogen receptor (ER) and/or progesterone receptor (PgR) positive invasive carcinoma of the breast (stage I-III) with no evidence of metastatic disease (M0).
• Must have completed mastectomy or breast sparing surgery, and must have recovered from all side effects of the surgery. Patients should have recovered from all grade 2 or higher side effects of chemotherapy and/or radiation therapy with the exception of alopecia and peripheral neuropathy. Concurrent bisphosphonate and trastuzumab therapies are allowed.
• Age > 18 years.
• Must have aromatase inhibitor (AI) associated musculoskeletal symptoms that began or increased after starting AI therapy and average pain of at least 2 (out of 10) on the BPI-SF. New musculoskeletal pain must not be due specifically to fracture or traumatic injury.
• Must currently be taking one of the following aromatase inhibitor (AI) doses for at least 14 days prior to registration and plan to continue for at least an additional 180 days after registration: * Anastrozole (Arimidex) 1 mg daily OR * Letrozole (Femara) 2.5 mg daily OR * Exemestane (Aromasin) 25 mg daily
• Must be postmenopausal, as defined by at least one of the following: * >= 12 months since their last menstrual period OR * Prior bilateral oophorectomy OR * Previous hysterectomy with one or both ovaries left in place (or previous hysterectomy in which documentation of bilateral oophorectomy is unavailable) AND (unless >= 60 years of age) follicle-stimulating hormone (FSH) values consistent with the institutional normal values for the post-menopausal state. OR * Receiving ovarian suppression such as via LHRH agonists.
• Performance status: Participants must have an ECOG performance status scale performance of 0-2 as assessed by medical doctor (MD) or registered nurse (RN).
• Participants must have no known allergy or hypersensitivity to vitamin B12.
• Must have completed the Brief Pain Inventory Short Form (BPI-SF) within 7 days prior to enrollment and have an “average pain” score of at least 2.
• Participants who are receiving treatment with narcotics, tramadol, gabapentin, and/or pregabalin must have been taking a stable dose for at least 30 days prior to registration.
• Participants must be able to complete study questionnaires in English or Spanish.
• Participants who are currently taking vitamin B12 or a multivitamin containing vitamin B12 will be able to participate in the study after having stopped taking the vitamin B12 or the multivitamin containing the B12 for at least two weeks.
• Participants must be willing to submit blood samples for laboratory testing [to test for serum vitamin B12, C-reactive protein (CRP), homocysteine level, phosphate, and methyl methacrylate (MMA)]. Baseline samples must be obtained prior to beginning protocol treatment.
• All participants or their legally authorized representative must be informed of the investigational nature of this study and must sign and give written informed consent in accordance with institutional and federal guidelines.
• Participants must have the ability to understand and the willingness to sign a written informed consent document.

Exclusion Criteria

• Participants receiving any other investigational agents.
• History of allergic reactions attributed to compounds of similar chemical or biologic composition to vitamin B12 or other agents used in this study.
• Participants with uncontrolled intercurrent illness including, but not limited to chronic liver disease, renal insufficiency (eGFR [estimated Glomerular Filtration Rate] or CrCl [creatinine clearance] 0.5), ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements.
• Participants reporting blurred vision will be excluded and referred to appropriate care.
• Participants with a history or family history of Leber optic neuropathy, or any other type of optic neuropathy.