C5AR1 and breast cancer: C5aR (also known as CD88) is a G‐protein–coupled receptor encoded by a gene on chromosome 19q13.3‐19q13.4.16 C5aR was originally reported to be expressed only in myeloid cells with no expression in lymphocytes and red blood cells, but a recent study found that many non‐myeloid–derived tumor cells also express C5aR, including lung cancer17, liver cancer,18 gastric cancer,19 renal cancer,20 breast cancer,21 and colon cancer22, and that the expression of C5aR is significantly higher in tumor cells compared with non‐tumorous tissues.