Inhibition of vascular endothelial growth factor (VEGF) signaling increases red blood cell (RBC) counts, and erythropoiesis markers have been proposed to guide antiangiogenic therapy in humans. We analyzed RBC measurements in patients enrolled in three studies: a phase II trial of axitinib in thyroid cancer; a study of sorafenib in advanced solid tumors; and a randomized trial of fluorouracil, hydroxyurea, and radiation with and without bevacizumab for head and neck cancer. In the sorafenib trial, plasma erythropoietin concentrations were measured at baseline, day 8, and day 35. Over the first 84 days of treatment, RBC counts increased for each day on sorafenib (2.7 M/μL [95% confidence interval (CI), 1.5-3.9]) and axitinib (4.3 M/μL [95% CI, 2.2-6.5]). RBCs declined over the first 68 days of cytotoxic chemoradiotherapy alone (-12.8 M/μL per day [95% CI, -15.7 to -9.8]) but less so with added bevacizumab (-7.2 M/μL per day [95% CI, -9.5 to -4.9]). Erythropoietin levels increased, on average, by 9.5 mIU/mL between day 8 and day 35 of sorafenib exposure. No significant relationships between elevations in RBCs and changes in volume status or blood pressure or between elevations in erythropoietin and smoking status were found. VEGF signaling inhibition is associated with increased RBC and erythropoietin production in humans. The effects of these changes are subtle at physiologic doses and are unlikely to be clinically useful biomarkers for guiding the administration of or predicting treatment responses to VEGF pathway inhibitors.
Keywords: Axitinib; Bevacizumab; Biological markers; Erythrocyte count; Erythropoietin; Sorafenib; Vascular endothelial growth factor A.