Gut microbiota and breast cancer: systematic review and meta-analysis.

Abstract

The gastrointestinal microbiota can modulate systemic estrogens, potentially influencing estrogen-induced breast neoplasia development. This study aimed to assess alterations in the gut microbiota in breast cancer patients. A search strategy was developed using the terms: "Microbiota," "Gastrointestinal Microbiome," "Breast Cancer," and synonyms. Ten observational studies were included. The total sample was 1730 women (929 cases and 801 controls). The meta-analysis of alpha diversity, assessed by the Shannon index, displayed that in the breast cancer group, the diversity of the gut microbiota was reduced compared to controls, with a standardized mean difference (SMD) of -0.34 (95% CI -0.59, -0.10, I2 = 68%, p = 0.007). Regarding the premenopausal population, there was a significant reduction in the breast cancer group (SMD -0.67, 95% CI -1.06, -0.28, I2 = 77%, p = 0.0009). In women with a body mass index (BMI) between overweight or obesity, no statistically significant difference was observed (SMD -0.20; 95% CI -0.51, 0.11; I2 52%, p = 0.20). However, in women with a BMI greater than or equal to 18.5 and less than 25.0, there was lower diversity in women with breast cancer compared to controls (SMD -0.49, 95% CI -0.94, -0.04; I2 78%, p = 0.03). The study found a significant difference in gut microbiota diversity between women with breast cancer and controls, supporting the growing evidence that the gut microbiota may play a role in mammary carcinogenesis.