Strength of ER-positivity in relation to survival in ER-positive breast cancer treated by adjuvant tamoxifen as sole systemic therapy.

AIMS: Oestrogen receptor (ER) positivity has been shown to be a predictive factor for response to endocrine treatment in breast cancer patients. Following breast surgery, adjuvant treatment is allocated according to various parameters (including Nottingham Prognostic Index (NPI), menopausal status and ER status). Patients whose cancer falls in the same NPI range may receive different adjuvant treatment according to ER status. The aim of our study is to assess whether the degree of ER-positivity, as measured immuno-histochemically by H-score (see definition in "Introduction" section) and percentage of ER-stained cells) has an influence on overall survival (OS) and disease-free survival (DFS) and whether this could be used to help determine adjuvant treatment.
MATERIALS AND METHODS: A review was undertaken of 563 post-menopausal patients receiving adjuvant tamoxifen and no chemotherapy following surgical resection of histologically proven ER-positive breast cancer. The impact of both H-score and percentage of cells staining for ER was assessed using OS and DFS over a 10-year period.
RESULTS: Patients were stratified into 4 groups according to ER H-score, namely those scoring ≤50, 51-100, 100-200, and >200. Ten-year survival was 84% for H-score above 200, 67% for H-score 100-200, 71% for H-score 50-100 and 41% for H-score less than 50 (p<0.001). Ten-year disease-free survival figures were similar, being 84% for H-score above 200, 73% for H-score 100-200, 83% for H-score 51-100 and 28% for H-score less than 50 (p<0.0001).
CONCLUSIONS: The data suggests that patients whose tumours only weakly manifest ER (H-score ≤50) fare less well in the long-term than patients whose tumours show more vigorous ER-staining when treated by endocrine therapy as sole systemic adjuvant treatment. This finding is relevant to decisions about adjuvant systemic therapy.