SPDL1 and melanoma: Serum levels of sPD-L1 have been negatively associated with overall survival or response to immunotherapy in diverse cancer types, including renal cell carcinoma, diffuse large B-cell lymphoma, multiple myeloma, melanoma, and lung cancer (Frigola et al., 2012; Frigola et al., 2011; Koukourakis et al., 2018; Okuma et al., 2017; Rossille et al., 2014; Wang et al., 2015; Zhou et al., 2017), suggesting a possible inhibitory effect.