ESR1 and breast cancer: In a retrospective study by Zelba et al., a prophylactic peptide vaccine was administered intradermally in four BC patients (1 case of TNBC, 2 case of ER positive BC, and 1 case of HER2 positive BC) who had achieved complete remission after chemotherapy, followed by subcutaneous and adjacent adjuvant administration (Zelba et al., 2022).