This study aims to explore the potential of ESR1 as a biomarker in breast cancer (BRCA) using bioinformatics analysis tools. The up-regulation of ESR1 expression in BRCA was investigated using UALCAN and GEPIA2, illustrating its role in BRCA progression. Furthermore, analyses based on various variables such as gender, age, race, and pathological stages of BRCA patients revealed a consistent up-regulation of ESR1, emphasizing its role in the development and progression of BRCA. Additionally, an analysis of ESR1 promoter methylation levels across various parameters revealed hypomethylation, affirming the inverse correlation between methylation and ESR1 expression. Prognostic analysis further indicated that overexpression of ESR1 is associated with poor overall survival, highlighting its potential as a prognostic biomarker in BRCA. Moreover, genetic mutation analysis using cBioPortal disclosed a minor role of ESR1 genetic mutations in BRCA, with only 2.5% of genetic alterations observed. The STRING and DAVID tools were utilized to conduct pathway enrichment analysis, revealing diverse biological functions of ESR1 and its 10 interconnected genes. Altogether, these results underscore the significance of understanding ESR1 up-regulation in BRCA and demonstrate its potential as a therapeutic, diagnostic, and prognostic biomarker.