Estrogen receptor analyses in the Danish Breast Cancer Cooperative Group. History, methods, prognosis and clinical implications

Introduction. Estrogen receptor (ER) is a prognostic and predictive biomarker, which has been known for 40 years. The detection method has developed over the years from different biochemical assays (BCA) to immunohistochemistry (IHC) on paraffin embedded tissue. The aim of the present study is to describe the development in ER analysis in the Danish Breast Cancer cooperative Group (DBCG), in the period of 1977 to 2006, regarding quantity and method of analyses. To compare BCA with IHC, and to report the prognosis for low-risk breast cancer patients. Patients and methods. In the period of 1991-1993, BCA and IHC were both performed on 2 364 tumours from breast cancer patients in Denmark. Three central laboratories in Copenhagen, Aarhus and Aalborg, respectively, performed BCA, while IHC was done in each of the pathology departments participating in the study. Data on ER status, clinical variables and prognostic factors were obtained from the DBCG database. Prognosis is calculated from the DBCG protocol 89a, regarding recurrence free survival (RFS) and overall survival (OS). Results. We find an increasing frequency of ER positive tumours over time, with correlation to patient age. There is a better RFS and OS for tumours positive in both ER determinations. However, BCA is more sensitive than IHC. We find a significant correlation between positive ER status and other low risk factors, except lymph node status. Discussion. Immunohistochemistry has several advantages compared with BCA; it is decentralised, only requiring small amounts of tumour tissue, with direct light microscopic interpretation of invasive tumour cells. It is less expensive and more rapid than BCA. Results in this study show the same RFS in both ER determinations. We conclude that IHC in analysing ER is a rapid, reliable and easy method, and we recommend the use of external quality control programme.