Effect of Vitamin D Supplementation on the Efficacy and Adverse Effects of Neoadjuvant Therapy in Patients with Breast Cancer

Inclusion Criteria: 1. Age between 18 and 80 years, with an Eastern Cooperative Oncology Group (ECOG) performance status of 0-2. 2. Primary diagnosis of breast cancer confirmed by preoperative pathological examination. 3. Serum 25(OH)D levels less than 20 ng/ml (50 nmol/L). 4. Patients who have not previously received chemotherapy and who plan to undergo at least 4 cycles of 5.neoadjuvant chemotherapy or combined targeted therapy. 6.Life expectancy of at least 6 months. 7.No other uncontrolled benign diseases at the time of recruitment. 8.All patients must have complete clinical medical records. 9.Willingness to voluntarily sign an informed consent form. Exclusion Criteria: 1. History of invasive breast cancer. 2. Prior systemic treatment for the treatment or prevention of breast cancer. 3. Known allergic reactions to vitamin D or calcium compounds. 4. Comorbidities that may affect vitamin D or calcium balance or bone health. 5. Vitamin D or calcium supplementation in the past 3 months. 6. Presence of other tumors. 7. Pregnant or lactating women. 8. Individuals who do not wish to participate in the study.