Objective  To investigate the clinical, pathological, and prognostic characteristics of luminal B breast cancer patients with diabetes.

  Methods  Atotal of 479 luminal B breast cancer patients with diabetes and 3 392 luminal B breast cancer patients without diabetes who were treated between January 2002 and December 2006 were enrolled in this study. The luminal B breast cancer patients were further divided into the luminal B (high ki67) and luminal B (Her-2/neu+) subgroups. Each subgroup was further grouped into metformin-treated, non-metformin-treated, and non-diabetic groups. The indicators included cancer-specific mortality, clinical, pathological stage, lymph node status, chemotherapy, and endocrine therapy. The survival analysis of each group was performed using the Kaplan-Meier method, and the significance was determined using the logrank test. Cox proportional hazard model was used to examine the correlation between each factor and the prognosis.

  Results  The Kaplan-Meier analysis results revealed that the breast cancer mortality rates in the metformin-treated, non-metformin-treated, and non-diabetic groups were significantly different in both luminal B (high ki67) and luminal B (Her-2/neu+) subgroups (logrank test: P < 0.001, P=0.035), and the respective five-year survival rates were 93.5%, 81%, and 89% for the luminal B (high ki67) subgroup and 84%, 77%, and 83% for the luminal B (Her-2/neu+) subgroup. The Cox multifactorial regression analysis results showed that compared with the metformin-treated group, the non-metformin-treated group was associated with a significantly increased risk of mortality (P < 0.001, P=0.044) in the two subgroups. Meanwhile, the non-diabetic group was associated with an increased risk of mortality (P=0.038) in the luminal B (high ki67) subgroup only. The percentage of elderly (P < 0.001), menopausal (P < 0.001), obese (P < 0.001), and patients with cardio-cerebrovascular complications (P < 0.001) tended to be higher in the metformin-treated and non-metformin-treated groups than in the diabetic group. Moreover, the metformin- and non-metformin-treated groups in the luminal B (high ki67) subgroup were associated with high percentages of T3/4 pathological stage (P < 0.001), lymph node metastasis (P=0.001). The non-metformin-treated group was associated with a lower percentage of invasive ductal carcinoma (P=0.001) compared with the other two groups.

  Conclusion  The non-metformin-treated group resulted in worse clinical outcomes in both subgroups compared with the metformin-treated group. Meanwhile, the non-diabetic group resulted in the worst prognosis among the three groups in the luminal B (high ki67) subgroup. These findings suggest that the choice of different anti-diabetic drugs may influence the prognosis of luminal B breast cancer patients with diabetes.