IntroductionMetformin use has recently been observed to decrease both the rate and mortality of breast cancer. Our study was aim to determine whether metformin use is associated with survival in diabetic breast cancer patients by breast cancer subtype and systemic treatment.MethodsData from the Asan Medical Center Breast Cancer Database from 1997 to 2007 were analyzed. The study cohort comprised 6,967 nondiabetic patients, 202 diabetic patients treated with metformin, and 184 diabetic patients that did not receive metformin. Patients who were divided into three groups by diabetes status and metformin use were also divided into four subgroups by hormone receptor and HER2-neu status.ResultsIn Kaplan-Meier analysis, the metformin group had a significantly better overall and cancer specific survival outcome compared with non metformin diabetic group (P <0.005 for both). There was no difference in survival between the nondiabetic and metformin groups. In multivariate analysis, Compared with metformin group, patients who did not receive metformin tended to have a higher risk of metastasis with HR 5.37 (95 % CI, 1.88 to 15.28) and breast cancer death with HR 6.51 (95 % CI, 1.88 to 15.28) on the hormone receptor-positive and HER2-negative breast cancer. The significant survival benefit of metformin observed in diabetic patients who received chemotherapy and endocrine therapy (HR for disease free survival 2.14; 95 % CI 1.14 to 4.04) was not seen in diabetic patients who did not receive these treatments.ConclusionPatients receiving metformin treatment when breast cancer diagnosis show a better prognosis only if they have hormone receptor-positive, HER2-positive tumors. Metformin treatment might provide a survival benefit when added to systemic therapy in diabetic patients.

Young breast cancer patients are more likely than old patients to experience ipsilateral breast tumor recurrence (IBTR) after breast conserving surgery (BCS). However, the pathological processes underlying this relationship have not been elucidated. We investigated the effect of young age on IBTR in a Korean cohort of women with different molecular subtypes of breast cancer. We analyzed data of 2,102 consecutive breast cancer patients who underwent BCS and post-surgical radiation therapy (RT) at two Korean institutions between 2000 and 2005. Patients were classified as young (≤ 40 years; N = 513) or old (> 40 years; N = 1,589). Breast cancer subtype was determined by estrogen receptor (ER), progesterone receptor (PR), and HER2. Median follow-up duration was 61 months. The 5-year IBTR rate was 3.4% in young patients and 1.1% in old patients (P < 0.001). Univariate analysis indicated that IBTR rate in young patients with luminal A and HER2 subtypes was significantly greater than in old patients with these subtypes (P = 0.015 and P < 0.001, respectively). Multivariate analysis, which used luminal A subtype in old patients as reference, indicated that HER2 subtype in young patients was associated with increased risk of IBTR (hazard ratio, HR = 12.24; 95% CI: 2.54-57.96). Among old patients, HER2 subtype was not associated with increased IBTR. In conclusion, young women had a higher rate of IBTR after BCS and RT than old women. This difference is mainly among women with HER2 subtype. Aggressive local control and adjuvant therapy should be considered for young women with HER2 subtype breast cancer.

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