Intratumoral cycling hypoxia inhibits expression level of estrogen receptor to promote the formation of heterogeneous sub-clones in luminal A breast cancer

Background The expression level of estrogen receptor (ER) is positively correlated with chemoresistance in patients with Luminal A tumor (LAT). ER expression level alters frequently after neoadjuvant chemotherapy which may be related with hypoxia. The spatial and temporal heterogeneity of tumor sub-clones is one of the major contributors to treatment failure. It is essential to investigate how the intratumoral heterogeneous sub-clones survive hypoxic microenvironment in LAT. Material and Methods LAT with largest cross section was divided into micro-sections, the expressions of hypoxia inducible factor-1 (HIF-1) and ER were then detected by immunohistochemistry. The intratumoral distribution of micro-vessels was assessed by 3D reconstruction and stained CD34; the cycling hypoxia model of MCF-7 was established in a step fashion to investigate the changes in HIF-1 and ER expressions. All statistical analyses were performed using SPSS software (version 17.0 for Windows). Results There was a negative correlation between the expressions of ER-alpha and HIF-1alpha (c=-2.40; p=0.044) as assessed by mean optical density values in the maximal cross section of tumor. As shown by 3D ultrasound image, the center of tumor had less functional micro-vessels compared with the periphery (P<0.05). From the periphery to the center of tumors in the large sections from 8 patients with LAT, the expressions of ER, progesterone receptor and CD34 were gradually decreased with HIF-1alpha expression showing an opposite direction. There was a negative correlation between expressions of ER-alpha and HIF-1alpha, and between expressions of CD34 and HIF-1alpha. No significant difference was noted in the outcomes of cytometry between the hypoxia and control groups. ER-alpha expression gradually decreased with the time course of cycling hypoxia with HIF-1alpha showing an opposite direction. Conclusion LAT is composed of heterogeneous sub-clone cells which can be distinguished by ER-alpha and HIF-1alpha. The distribution of heterogeneous sub-clone cells was closely related with heterogeneous microenvironment of hypoxia / reoxygenation. Keywords: Luminal A breast cancer, cycling hypoxia, estrogen receptor, heterogeneous sub-clones.