ESR1 and breast cancer: A subset of the gut microbiota, referred to as the estrobolome, has been linked to a high level of circulating estrogens in postmenopausal estrogen receptor (ER)-positive BC patients, while a diet, which is one of the strongest modulators of the gut microbiota, enriched with mono- and polyunsaturated fatty acids, fruits, vegetables, and legumes may reduce BC risk and mortality (14, 41).