HOXD13 and metastatic melanoma: In a recent study of 41 patients with metastatic melanoma, the plasma levels of soluble PD-1 (sPD-1), soluble programmed cell death ligand 1 (sPD-L1), butyrophilins (BTNs) 2A1, 3A1, and body mass index (BMI) were evaluated as predictors of the efficacy of anti-PD1 therapy.