Vitamin D Deficiency and Breast Cancer Recurrence in Indonesian Women with Breast Cancer: A Prospective Cohort Study

Introduction: Breast cancer remains the most common malignancy and a leading cause of cancer-related mortality among women worldwide, including in Indonesia. Vitamin D deficiency is frequently observed among breast cancer patients. Recent evidence has revealed the potential role of vitamin D in regulating tumor cell proliferation, differentiation, and apoptosis. Moreover, vitamin D deficiency has been associated with increased cancer risk and poorer clinical outcomes in breast cancer. This study aims to determine the frequency and prognostic significance of vitamin D deficiency in Indonesian women with breast cancer. Methods: A prospective study was conducted involving 123 women diagnosed with primary, nonmetastatic invasive breast cancer. Serum 25(OH)D levels were measured at diagnosis, prior to any treatment, using the Chemiluminescent Microparticle Immunoassay (CMIA) method. Vitamin D deficiency was defined as serum levels below 20 ng/mL. Results: The median serum vitamin D level was 19.9 ng/mL (range: 5.7–35.1). Vitamin D deficiency was identified in 65 patients (52.8%). It was significantly associated with higher tumor grade (p = 0.037), lymph node involvement (p = 0.012), larger tumor size (p = 0.041), more advanced clinical stage (p = 0.049), and positive expression of estrogen receptor (ER) (p = 0.034) and HER2 (p = 0.014). Kaplan–Meier analysis demonstrated that patients with vitamin D deficiency had a significantly shorter time to breast cancer recurrence (20.11 ± 0.91 months; p = 0.048). Multivariate Cox regression confirmed vitamin D deficiency as an independent predictor of shorter time to breast cancer recurrence (HR: 3.19; 95% CI: 1.178–8.660; p = 0.023). Discussion: These findings suggest that vitamin D deficiency may serve as a modifiable prognostic biomarker in breast cancer. Its association with aggressive tumor characteristics and shorter time to breast cancer recurrence highlight the potential value of assessing and correcting vitamin D status as part of breast cancer management, especially in Indonesian population. conclusion: Vitamin D deficiency may negatively impact time to tumor recurrence and is associated with multiple poor prognostic indicators in breast cancer, including grade, lymph node status, tumor size, clinical stage, and hormone receptor expression. Conclusion: Vitamin D deficiency is common among Indonesian women with breast cancer and independently associated with multiple poor prognostic indicators and shorter time to reccurence.