Background and purpose: Vitamin D (VitD) is a steroid hormone. This study aimed to detect the level of 25-hydroxy VitD ［25 (OH) D］ which is a serum biomarker of VitD status in peripheral blood of patients with breast cancer

and to explore the correlation b

etween VitD and clinicopathologic characteristics of breast cancer patients. Methods: We measured the level of 25 (OH) D in 109 breast cancer patients

50 patients with benign breast tumors and 2 000 healthy subjects in our hospital from January 2015 to July 2018 by a chemiluminescent immunoassay method. Flow cytometry was used to detect the immune function of T cells and the level of NK cells in the peripheral blood of breast cancer patients. Furthermore，the expression of VitD receptor (VDR) in breast cancer tissues was detected by immunohistochemistry. Results: The level of 25 (OH) D in peripheral blood of patients with breast cancer was significantly lower compared with patients with benign breast tumors or healthy subjects (P0.05). There was no significant difference in peripheral blood 25 (OH) D levels between patients with benign breast tumors and healthy subjects (P0.05). The level of 25 (OH) D in breast cancer patients was significantly associated with the immune function of T cells (CD4

+

/CD8

+

ratio)

clinical stage

lymph node metastasis

bone metastasis and progesterone receptor (PR) positivity

whereas serum 25 (OH) D level had no relation to the tumor size

the quantity of NK cells and the level of estrogen receptor (ER) (P0.05). There was a statistically significant correlation between the expression of VDR in breast cancer tissues and the level of hormone receptor (ER and PR) (P0.05)

while positive expression of VDR was not associated with the immune function of T cells

clinical stage

tumor size

bone metastasis and lymph node metastasis (P0.05). Conclusion: Low levels of VitD in peripheral blood may be associated with high risk of breast cancer

poor T cell immune function and poor prognosis.