Li et al. [93] used multiplexing SERS to achieve ultrasensitive detection of multiple soluble cancer protein biomarkers—for example, soluble programmed death 1 (sPD-1), soluble programmed death-ligand 1 (sPD-L1), and soluble epithermal growth factor receptor (sEGFR)—which are linked to the progression of the tumour, as well as the efficacy of the cancer therapy. Here, SPDL1 is linked to cancer.