Recently, several molecules and inflammatory markers, such as retinol-binding protein 4 (RBP4), angiopoietin-2 (Ang-2), neutrophil-lymphocyte ratio (NLR), and pan-immune-inflammation value (PIV), were identified as biomarkers of disease severity in patients with HS [5,6,7,8]. Here, RBP4 is linked to histiocytic sarcoma.