Background: An immunohistochemical (IHC) method is commonly used for determining estrogen receptor (ER) and progesterone receptor (PR) status in breast cancer. However, the proper cut-off points of IHC have not been established. Cut-off points for ER and PR status as predictive factors for endocrine therapy are needed.
Methods: A total of 249 cases of female breast cancer were enrolled. ER and PR status by IHC were analyzed using the proportion of stained cells and staining intensity by Allred's score.
Results: Proportion score (PS) and intensity score (IS) were related to enzyme immunoassay (EIA) titers, for both in ER and PR (p < 0.0001, all). PS correlated with IS in both ER and PR (R = 0.47 and 0.41, respectively). ER status by IHC was related to tumor size and lymph node status, while PR was related to tumor size and menopausal status. In 152 patients who received endocrine therapy with a median follow-up term of 38 months, differences in disease-free survival were most significant using a cut-off point of PS 3 which indicated more than 10 % of cells stained positively for both ER and PR (p = 0.0007 and 0.0087, respectively). In addition, combination analysis of ER and PR using this cut-off point revealed a notable prognostic difference.
Conclusion: A 10 % staining proportion may be an acceptable cut-off point for both ER and PR status by IHC, in terms of predicting response to endocrine therapy in breast cancer.