Vitamin D: An Ally in the Battle Against Breast Cancer

Breast cancer, with approximately 3,000 new diagnoses annually, represents the most frequently diagnosed malignancy and the third leading oncological cause of mortality among women. The majority of breast cancer cases are diagnosed in older women between the ages of 65 and 69 years. Notwithstanding the higher incidence in older women, breast cancer may also affect younger women; therefore, it is paramount to initiate regular breast self-examination and routine clinical surveillance at an early age. 

Histopathological Subtypes 

Breast cancer may be stratified into distinct molecular subtypes based on the immunohistochemical expression of the estrogen receptor (ER), progesterone receptor (PR), HER2 receptor, and the proliferation index Ki-67. According to this classification, breast carcinomas are grouped into four categories: Luminal A (LumA), Luminal B (LumB), HER2-positive, and Basal-like. The Basal-like subtype encompasses carcinomas that are negative for ER, PR, and HER2 receptors, designated as triple-negative breast cancer (TNBC). 

Treatment of Breast Carcinoma 

Therapeutic strategies for breast cancer encompass chemotherapy, surgical resection, hormonal therapy, and radiation therapy. Notably, one study demonstrated that patients with triple-negative breast cancer had significantly lower serum vitamin D levels compared to patients with ER-positive disease, with both groups exhibiting lower vitamin D concentrations than patients with benign breast conditions. 

Vitamin D₃ — An Ally in the Fight Against Tumors? 

Vitamin D₃ (cholecalciferol), the natural form of vitamin D, can be obtained from dietary sources and is also synthesized in human skin upon exposure to ultraviolet radiation from the precursor 7-dehydrocholesterol. Its biologically active metabolite, 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃), is primarily recognized as a critical regulator of calcium and phosphate homeostasis. Its biological effects are mediated through binding to the vitamin D receptor (VDR), a transcription factor that governs gene expression in target tissues such as the intestine, kidneys, and bone. VDR is also expressed in numerous other tissues, including neoplastic tissue, where it exerts antiproliferative, differentiation-inducing, and immunomodulatory effects. Preclinical in vitro and in vivo studies have demonstrated that 1,25(OH)₂D₃ modulates multiple signaling pathways involved in cellular proliferation, apoptosis, differentiation, inflammation, invasion, and angiogenesis. 

A Critical Appraisal of the Evidence 

Epidemiological studies suggest a lower risk of breast cancer among women with elevated serum 1,25(OH)₂D₃ concentrations compared to those with low levels. The association appears to be particularly strong when measurements are obtained during the summer months.   . However, aggregate analyses have not consistently demonstrated statistically significant correlations. Low vitamin D levels have been associated with adverse prognostic parameters in postmenopausal patients and with increased disease risk irrespective of menopausal status. Nevertheless, the findings of clinical trials have not fully corroborated the observations derived from epidemiological studies. Clinical trials have demonstrated that vitamin D supplementation (approximately 24 μg/day) does not reduce the risk of breast cancer by more than 30%. Furthermore, in a separate study, daily doses of 400 IU of vitamin D (10 μg) combined with 1,000 mg of calcium carbonate did not significantly reduce the risk of breast cancer or other invasive malignancies. 

Future Therapeutic Perspectives 

The majority of randomized controlled clinical trials do not demonstrate a clear reduction in breast cancer incidence with vitamin D₃ supplementation. Nevertheless, 1,25(OH)₂D₃ and its synthetic analogs may possess greater anticancer potential in breast cancer when administered in combination with established oncological therapies. Further research is warranted to establish the efficacy of vitamin D₃ analogs in combination regimens for the treatment of distinct breast cancer subtypes. Although in vitro and in vivo studies yield promising results regarding the use of 1,25(OH)₂D₃ or its analogs in attenuating tumor growth and progression, their clinical application in humans requires further investigation.