In addition to its major membrane-bound form, a soluble form of PD-L1 (sPD-L1) has long been documented in healthy human serum and found elevated in autoimmune disease and in cancer (Chen et al., 2011; Frigola et al., 2011; Koukourakis et al., 2018; Okuma et al., 2017; Rossille et al., 2014; Wan et al., 2006; Wang et al., 2015; Zhou et al., 2017; Zhu and Lang, 2017). Here, SPDL1 is linked to cancer.