BEST1 Positive Monocytes in Circulation: Visualize Intratumoral Crosstalk between Cancer Cells and Monocytes

Head and neck squamous cell carcinomas (HNSCCs) are characterized by an abundance of monocytes and macrophages recruited from the peripheral blood. However, it has not been determined whether these infiltrated cells can be released back into circulation with a tumor‐associated neobiosignature. This study reports that Bestrophin1 (BEST1), a component protein of Ca(2+)‐activated Cl(−) channels (CaCCs), is highly expressed on classical monocytes in the peripheral blood of HNSCC patients. This is due to monocyte education by tumor cells, in which tumoral VEGF‐A upregulates BEST1 expression on monocytes through the MEK‐ERK‐ELK1 pathway. This leads to improved secretion of IL‐6 and IL‐8, which promotes tumor cell proliferation. This work also finds that BEST1 facilitates the motility of monocytes, contributing to the migration of these cells back into circulation. These results suggest that the expression of BEST1 on peripheral monocytes may be a potential tool for monitoring tumor progression, and opens up the possibility of searching for cancer biomarkers on monocytes rather than on the tumor or its products.