The clinical data of breast cancer chemotherapy patients （case group，n=62） and healthy subjects （control group，n=48） were retrospectively analyzed.According to the serum levels of vitamin B12（VitB12），vitamin B9（VitB9） and vitamin B6（VitB6）， the breast cancer patients were divided into six subgroups：VitB12<0.025 μg·L^－1 group and VitB12≥0.025 μg·L^－1group，VitB9<3.93 μg·L^－1group and VitB9≥3.93 μg·L^－1 group， VitB6<1.955 μg·L^－1 group and VitB6≥1.955 μg·L^－1 group.The baseline characteristics and chemotherapy regimens of breast cancer patients in different subgroups were analyzed.The patients in case group were divided into AC-T group（n=21），EC-T group（n=22），TC group（n=11），and the other chemotherapy regimen group （n=8） according to the chemotherapy regimen. In the first chemotherapy cycle， in the early morning of the second day after infusion of all chemotherapeutics， the fasting serum was collected from the patients， and the serum B vitamin levels of the subjects in two groups were detected by liquid chromatography-tandem mass spectrometry.The levels of serum vitamin B in breast cancer patients with different chemotherapy regimens and the chemotherapy regimens of breast cancer patients with different serum B vitamins levels were compared and analyzed.

The level of serum VitB9 in the subjets in control group was significantly higher than that in case group （t=－3.343，P<0.05）.The serum levels of VitB12 and VitB6 in the patients in case group had no significant differences compared with control group（P>0.05）. There was a statistically significant difference in menopause or not between VitB12<0.025 μg·L^－1 group and VitB12≥0.025 μg·L^－1 group（t=7.127，P=0.008）.There were no statistically significant differences in age， body mass index（BMI）， TNM stage， tumor size， lymph node metastasis， estrogen receptor （ER）， progesterone receptor （PR），human epidermal growth factor receptor-2（Her-2），Ki-67， and pathological classification between VitB12<0.025 μg·L ^－1group and VitB12≥0.025 μg·L ^－1 group（P>0.05）；there was a statistically significant difference in lymphnode metastasis between VitB6<1.955 μg·L^－1 group and VitB6≥1.955 μg·L ^－1 group（t=6.057，P=0.014）；there were no statistically significant differences in age， BMI， menopause or not ， TNM stage， tumor size， ER， PR， Her-2， Ki-67， and pathological types between VitB6<1.955 μg·L^－1 group and VitB6≥1.955 μg·L^－1 group （P>0.05）.There were no significant differences in age， menopause or not， BMI， TNM stage， tumor size，lymphnode metastasis， ER，PR，Her-2，Ki-67， and pathological classification between VitB9<3.93 μg·L^－1 group and VitB9≥3.93 μg·L^－1 group（P>0.05）. Among the 62 breast cancer patients included， 11 cases were treated with TC chemotherapy regimen， 21 cases were treated with AC-T chemotherapy regimen，22 cases were treated with EC-T chemotherapy regimen， and 8 cases were treated with other chemotherapy regimens；there were no significant differences in the serum levels of VitB12， VitB9 and VitB6 among the breast cancer patients received different chemotherapy regimens（P>0.05）.

There are no significant differences in the serum vitamin B levels in the breast cancer patients received different chemotherapy regimens， but there is a significant difference in the serum VitB9 level in the breast cancer chemotherapy patients compared with normal controls.