Vitamin B12 for Aromatase Inhibitors Associated Musculoskeletal Symptoms in Breast Cancer

Treatment of hormone receptor (HR)-positive breast cancer with Aromatase Inhibitors (AIs) can lead to associated musculoskeletal pain and may cause patients to discontinue important treatment. This is a randomized controlled trial assessing the affect of Vitamin B12 on AI-associated joint pain and other outcomes. Participants will be randomly assigned 1:1 to treatment or control arm. The primary objective of this study is: -To assess whether daily oral Vitamin B12 decreases average joint pain in women with AI-Associated Musculoskeletal Symptoms Secondary objectives include: * To investigate whether daily vitamin B12 improves functional quality of life * To explore the impact of treatment on serum inflammatory cytokine levels (C- reactive protein) between baseline and various points in treatment.