Expression of Erythropoietin and Erythropoietin Receptor in Squamous Cell Carcinomas of the Head and Neck: Levels of Erythropoietin Expression Correlate with Tumor Hypoxia.

Erythropoietin (EPO), an oxygen-regulated glycoprotein hormone, is a hematopoietic cytokine that stimulates erythropoiesis by binding to its cellular receptor EPOR. The recombinant form of human EPO is widely used in clinical practice for the prevention or treatment of anemia associated with cancer and chemo-radiation therapy. However, in a recent randomized, placebo-controlled trial involving patients receiving curative radiotherapy for squamous cell carcinoma of the head and neck, EPO treatment was associated with poorer loco-regional progression-free survival. The purpose of this study was to determine whether EPOR and its ligand EPO are expressed in primary squamous cell carcinomas of the head and neck. We also investigated the hypothesis that EPO expression in malignant cells may be associated with the presence of tumor hypoxia, an important factor involved in resistance to radiation treatment, tumor aggressiveness and poor prognosis. Twenty-one patients with squamous cell carcinoma of the head and neck were enrolled in a tumor hypoxia study under a research protocol approved by the Institutional Review Board at the University of North Carolina Hospitals. All patients provided signed informed consent. The patients received an intravenous infusion of the hypoxia marker pimonidazole hydrochloride (Hypoxyprobe-1™) prior to multiple tumor biopsies. Two or more biopsies were available from all except one primary tumor. The tissue specimen from one patient with laryngeal carcinoma was excluded because of availability of only a single, small and fragmented biopsy. Contiguous sections from 74 biopsies were analyzed by immunohistochemistry for expression of EPOR and EPO as well as pimonidazole binding. We found EPOR expression in tumor cells in 97% of the biopsies. The pattern of EPOR immunoreactivity was predominantly cytoplasmic but was found to be localized to the membrane in some sections. Co-expression of EPO was observed in 90% of biopsies. Qualitative and semi-quantitative analyes for EPO staining and tumor hypoxia on a section-by-section basis revealed that EPO and pimonidazole adduct staining did not always co-localize within tumors but there was a significant positive correlation between levels of micro-regional EPO expression and pimonidazole binding (r = 0.736, P < 0.001, n=20 by two-tailed Spearman’s rank correlation analysis). These data demonstrate the co-expression of EPOR and its ligand EPO in squamous carcinoma cells suggesting that EPO may play a novel role as a potential autocrine or paracrine growth factor in head and neck cancer. Furthermore, EPO expression in tumor cells may be modulated, at least in part, by tumor hypoxia. The expression of EPOR needs to be taken into consideration in the design of future clinical trials investigating the role of recombinant human EPO in head and neck cancer.