SPDL1 and breast carcinoma: The median sPD-L1 level in plasma collected from all recurrent/metastatic breast cancer cases before first-line rescue therapy was 7.964 ng/ml (range: 1.442–21.618), apparently higher than that of control cohorts of 30 early breast cancer patients at diagnosis (median: 4.891 ng/ml, range: 1.249–10.718, p < 0.001, Fig. 1a).