Association of the Estrogen Receptors Beta Expression with the Ki-67 Proliferative Index in Breast Cancer

Background. Estrogen receptors beta (ERβ) are an important biological regulator and target of antiestrogens, however, unlike estrogen receptors alpha (ERɑ), their significance in the prognosis and treatment of breast cancer remains unclear. Purpose. Evaluation of the ERβ prognostic value in the comparative assessment of frequency and level of the marker expression in groups with good and poor prognosis by Ki-67 proliferative index score in breast cancer. Methods. ERβ expression level (% of cells expressing the marker) in 68 breast tissue samples was quantified by immunofluorescence and flow cytometry. Primary antibodies to ERβ (clone 14C8, ab288) and secondary antibodies conjugated with DyLight650 (ab98729) were used. In the same samples, the Ki-67 expression level was assessed by the immunohistochemical method. Results. The ERβ and Ki-67 were detected in 100% breast tissue samples with high heterogeneity of the markers’ expression in different patients. Statistical analysis of good and poor prognosis in accordance with the Ki-67 proliferative index score (Ki-67≤20% and Ki-67>20%) showed the prognostic value of the ERβ expression level of 50%. There was no association between the Ki-67 and ERβ expression levels in the same tumor sample (Spearman's rank correlation coefficient R=–0,16; P>0,05). At the same time, high expression of ERβ≥50% was 2,3 times more frequently detected in the good vs poor prognostic group by Ki-67 — 41% vs 18%, P=0,02. Conclusion. The ERβ expression level ≥50% in the tumor can be considered as a factor of good prognosis of breast cancer.