Prognosis, stage and oestrogen receptor status of contralateral breast cancer in relation to characteristics of the first tumour, prior endocrine treatment and radiotherapy

Our results suggest that both the residual prognostic impact of BC1, the possibility of contralateral metastasis, as well as prior treatment given, need to be considered when determining appropriate diagnostic work-up and treatment of CBC. In addition, radiation to the contralateral breast and risk of inducing CBC with an aggressive ER-negative phenotype should be considered when establishing new radiation treatment techniques. This study indicates loss of ER-expression as an important 'endocrine treatment escape mechanism', although further studies are warranted.