ESR1 and breast neoplasm: However, the specific effect of BRCA2 deficiency on ER signaling remains poorly understood.<h4>Aims</h4>This study aimed to elucidate the relationship between BRCA2 deficiency and ER signaling using integrated clinical and in vitro analyses.<h4>Methods and results</h4>Immunohistochemical analyses were performed on ER-positive/HER2-negative breast tumors from BRCA2 PV carriers (n = 8) and BRCA2 wild-type patients (n = 59).