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

Abstract

Aim: A contralateral breast cancer (CBC) is today treated as an independent primary tumour, although recent data suggest risk and prognosis of CBC to be influenced by characteristics of and treatment given for the first tumour (BC1). We hereby investigate phenotypical and prognostic features of the second tumour (BC2) in relation to prior endocrine treatment and radiotherapy.

Methods: From a well-defined population-based cohort of CBC-patients, we have constructed a unique tissue-microarray including 600 pairs of primary tumours and CBCs. Breast cancer mortality was primary end-point for prognosis.

Results: Both oestrogen receptor (ER) status and stage was strongly correlated between BC1 and BC2 within CBC-pairs. Although BC2 had the highest prognostic impact, BC1 continued to influence prognosis after diagnosis of CBC. Patients diagnosed with two high stage tumours within a short time-interval had a particularly bad prognosis. Prior endocrine therapy and radiotherapy both correlated to ER-negativity of BC2. An ER-negative BC2 was associated with an inferior prognosis compared to an ER-positive BC2 regardless of ER-status of BC1 or prior endocrine therapy.

Conclusions: 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.

Keywords: Breast neoplasms; Hormonal antineoplastic agents; Humans; Neoplasm staging; Oestrogen receptor; Progesterone receptor; Prognosis; Radiotherapy; Tamoxifen; Tissue microarray analysis.