Introduction: Breast cancer is the most common cancer and the leading cause of cancer death among women in the world. Given the potential relationship between vitamin B12 deficiency and cancer progression, the present study investigated the possible relationship between vitamin B12 deficiency and some of the factors affecting the prognosis of breast cancer.

Materials and Methods: This cross-sectional and descriptive-analytical study was performed on 63 patients with breast cancer who met the inclusion criteria. Serum levels of vitamin B12 were requested for all patients and the required information was collected in the relevant forms. The relationship between serum vitamin levels and desired factors was investigated by relevant statistical tests.

Results: It was found that only 15.9% of breast cancer patients had normal serum levels of vitamin B12 and others had some degree of deficiency. There was also an inverse relationship between age and serum levels of vitamin B12, but this relationship was not statistically significant (P=0.855). It was also found that the serum level of vitamin B12 is significant with tumor status in terms of PR (P=0.03) and it is notablewith tumor status in terms of ER (P=0.09).

Conclusion: Considering the significant relationship between serum levels of vitamin B12 and PR in breast cancer, further studies with larger sample sizes are suggested to clarify the relationship between these two factors.

Keywords: Breast cancer, Cobalamin, Vitamin B12 deficiency, Estrogen receptor