Background: Accurate assessment of estrogen (ER) and progesterone (PR) receptors is critical in predicting the response to endocrine therapies in breast cancer.
Material and methods: From a series of 360 patients with breast invasive carcinoma assessed for hormone receptors by immunohistochemistry (IHC) in the 90's, we re-analysed, on the same tumour material, the cases considered negative (n = 164), i.e., ER-/PR- (n = 95), ER+/PR- (n = 63) and ER-/PR+ (n=6), and 16 of 196 ER+/PR+ tumours with unfavourable outcome. Concordance between the previous IHC (Streptavidin-Biotin-Peroxidase) method and the current one (Peroxidase-Indirect-Polymer) was determined by the McNemar's test. Relapse-free (RFS) and overall survival (OS) were estimated by the Kaplan-Meier method.
Results: From 101 ER- and 158 PR- cases, 38 (37.6%) and 58 (36.7%) became positive, increasing ER and PR expression from 71.9% and 56.1% to 82.5% and 72.2%, respectively (P<0.001). All 16 ER+/PR+ cases maintained their co-positivity, while all ER-/PR+ tumours changed to ER positive. Kaplan-Meier survival curves showed significant differences related to RFS and OS for PR, either in the whole series or in the subset (n = 151) submitted to hormonal treatment. The patients' subgroup with ER+/PR- tumours exhibited the worst prognosis.
Conclusion: The current IHC method improves the clinical usefulness of ER/PR assessment by decreasing the rate of false negative results.
Keywords: Breast cancer; Estrogen receptors; Immunohistochemistry; Progesterone receptors; Prognosis.