CCL2 is a prognostic biomarker in mastocytosis. (A-B) CCL2 serum levels of mastocytosis patients compared with (A) an age- and sex-matched control cohort and (B) between subgroups of mastocytosis (cutaneous mastocytosis [CM], mastocytosis in the skin [MIS], ISM, advanced SM). (C-D) Serial sections prepared from paraffin-embedded BM of a patient with SM were stained by immunohistochemistry using (C) an anti-tryptase antibody (pink staining) or (D) an anti-CCL2 antibody (brown staining). Neoplastic MC infiltrates were found to stain positive for CCL2. Lower subpanels show a higher magnification (original magnification ×400) of the upper subpanels (original magnification ×100). (E-F) Kaplan-Meier plot for overall survival of mastocytosis patients stratified according to the upper reference range of CCL2 serum level of 468 pg/mL. The difference in the probability of survival was significant for (E) all mastocytosis patients and (F) the subgroup of patients with ISM. *P < .05, **P < .01