SPDL1 and plasma cell myeloma: Since soluble PD-L1 (sPD-L1) has been detected in the peripheral blood of many cancer patients including advanced non-small cell lung cancer, multiple myeloma, diffuse large B-cell lymphoma, and renal cell carcinoma, and high levels of sPD-L1 are associated with poor prognosis, sPD-L1 can serve as a surrogate marker for PD-L1 on TNBC.