Background: Obesity, with increasing worldwide prevalence, is associated with increased breast cancer burden. The association is attributed to multiple metabolic disturbances including chronic inflammation due to dysfunctional adipose tissue. Features of local breast adipose tissue inflammation such as macrophage infiltration and an enriched pro-inflammatory gene signature were recently reported in mouse models of obesity and in women with high adiposity or metabolic disorders. Strategies that can reduce obesity-induced chronic inflammation may lead to reduction of breast cancer risk. Metformin, a widely used anti-diabetic drug, exerts favorable effects on multiple metabolic disturbances. This study aims to evaluate the clinical effects of metformin on breast tissue inflammation. Methods: Macrophage infiltration and polarization were determined in breast core needle biopsies collected at baseline and 6 months after agent intervention from a Phase II randomized, double-blind, placebo-controlled trial of metformin in premenopausal women with components of metabolic syndrome. Macrophage infiltration was assessed using a pan macrophage marker (CD68) by immunohistochemistry (IHC). M1 and M2 macrophages were assessed using CD40 and CD206 surface markers, respectively, by IHC. The primary endpoint is the change in macrophage density in breast adipose tissue. Secondary endpoints include the change in macrophage density in breast stroma and epithelium tissues, the proportion of M1 (pro-inflammatory) and M2 (anti-inflammatory) macrophages in breast adipose, stroma, and epithelium tissues. Results: Baseline biopsies from 76 participants (40 in the metformin arm and 36 in the placebo arm) were available for CD68 analysis. The baseline CD68 density was 22.48 ± 3.25, 67.26 ± 9.68, 418.81± 71.02 (mean±SE) per mm2 in breast adipose, stroma, and epithelium tissues, respectively. Biopsies from 71 participants (34 in the metformin arm and 37 in the placebo arm) were available for CD68 analysis at 6 months. Comparing to placebo, metformin intervention led to a significant reduction in CD68 density in breast adipose tissue (p = 0.01) but did not change the CD68 density in breast epithelium and stroma tissues. Conclusion: Metformin intervention resulted in favorable changes in macrophage infiltration in breast adipose tissue in premenopausal women with component of metabolic syndrome. Studies are ongoing to evaluate the effects of metformin on macrophage polarization. Citation Format: Liane E. Pinto, Sara Centuori, Jose Guillen-Rodriguez, Denise J. Roe, Edgar Tapia, Pavani Chalasani, H-H. Sherry Chow. Effects of metformin on breast tissue inflammation in premenopausal women with components of metabolic syndrome. [abstract]. In: Proceedings of the AACR Special Conference: Precision Prevention, Early Detection, and Interception of Cancer; 2022 Nov 17-19; Austin, TX. Philadelphia (PA): AACR; Can Prev Res 2023;16(1 Suppl): Abstract nr P065.

Background: The increasing rate of obesity in the United States is accompanied by serious health concerns. Obesity increases breast cancer burden and is associated with increased risk of triple-negative breast cancer in premenopausal women and overall poor prognosis in breast cancer patients. There is a need for intervention strategies aiming to reduce obesity-associated dysregulation to attenuate breast cancer risk.Methods: We conducted a Phase II, double-blind, randomized, placebo-controlled clinical trial in overweight/obese premenopausal women with elements of metabolic syndrome to assess the potential of metformin to reduce obesity-associated breast cancer risk. Study participants received metformin (850 mg BID, n = 76) or placebo (n = 75) for 12 months. Fasting blood samples were collected at baseline, 6-months and 12-months from each participant. We analyzed the effects of metformin on circulating levels of insulin/IGF axis, adipokines, and neutrophil-to-lymphocyte ratio in samples collected from this trial. Serum concentrations of insulin, IGF-1, IGFBP-3, leptin and high-molecular weight adiponectin were measured using ELISA immunoassays. Results: The study population included 151 women and had a mean age of 39.5 years, mean body mass index (BMI) was 37.8 and study participants had a large waist and at least one other component of metabolic syndrome. Metformin treatment did not result in significant changes in members of the insulin/IGF axis compared to the placebo group, however, limiting the analysis to participants with detectable metformin in the blood serum resulted in favorable changes in insulin (p=0.0215), HOMA-IR (p<0.001) and a significant increase in IGFBP-3 (p=0.0176) in the metformin group after the intervention. We observed significant decreases in leptin (p=0.0018) and the leptin-to-adiponectin ratio (p=0.0036) in the metformin arm longitudinally. Additionally, we observed a significant reduction in the neutrophil-to-lymphocyte ratio (NLR), a systemic inflammation marker, in the metformin group compared to the placebo group (p=0.0170). Conclusions: We conclude that metformin led to favorable changes in metabolic markers associated with breast cancer risk in the metformin treated participants, however, the changes were not significantly different from the placebo group. The NLR was significantly reduced after metformin intervention compared to the placebo group. More research is needed to understand the effects of metformin on the insulin/IGF axis and adipokines in overweight/obese premenopausal women. Citation Format: Edgar Tapia, Diana Villa-Guilen, Pavani Chalasani, Sara Centuori, Denise J. Roe, Jose Guillen, Catherine Cordova, Liane Pinto, Sherry Chow. Effect of metformin on metabolic markers associated with breast cancer risk in a phase II clinical trial in overweight/obese premenopausal women [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-10-02.

Obesity is a known risk factor for post-menopausal breast cancer and may increase risk for triple negative breast cancer in premenopausal women. Intervention strategies are clearly needed to reduce obesity-associated breast cancer risk. We conducted a Phase II double-blind, randomized, placebo-controlled trial of metformin in overweight/obese premenopausal women with components of metabolic syndrome to assess the potential of metformin for primary breast cancer prevention. Eligible participants were randomized to receive metformin (850 mg BID, n = 76) or placebo (n = 75) for 12 months. Outcomes included breast density, assessed by fat/water MRI with change in percent breast density as the primary endpoint, anthropometric measures, and intervention feasibility. Seventy-six percent in the metformin arm and 83% in the placebo arm (p = 0.182) completed the 12-month intervention. Adherence to study agent was high with more than 80% of participants taking ≥ 80% assigned pills. The most common adverse events reported in the metformin arm were gastrointestinal in nature and subsided over time. Compared to placebo, metformin intervention led to a significant reduction in waist circumference (p < 0.001) and waist-to-hip ratio (p = 0.019). Compared to placebo, metformin did not change percent breast density and dense breast volume but led to a numerical but not significant decrease in non-dense breast volume (p = 0.070). We conclude that metformin intervention resulted in favorable changes in anthropometric measures of adiposity and a borderline decrease in non-dense breast volume in women with metabolic dysregulation. More research is needed to understand the impact of metformin on breast cancer risk reduction. ClinicalTrials.gov NCT02028221. Registered January 7, 2014, https://clinicaltrials.gov/ct2/show/NCT02028221