Clinical impact of skin lesions in mastocytosis: a multicenter study of the European Competence Network on Mastocytosis (ECNM)

Mastocytosis is a rare neoplasm characterized by expansion and accumulation of mast cells in various organ systems. Systemic mastocytosis (SM) may or may not presents with cutaneous lesions. To examine the frequency and clinical impact of cutaneous involvement, 1510 mastocytosis patients collected in the registry of the European Competence Network on Mastocytosis were analyzed. Cutaneous involvement was found in 1195/1510 (79.1%) patients. Of these, 286 had cutaneous mastocytosis (CM) and 721 had SM with skin involvement (SM+). Adult patients with skin involvement who did not have a bone marrow examination (n=188) were defined as mastocytosis in the skin (MIS). In 315 patients with SM, no skin involvement was found (SM-). The percentage of cases with cutaneous involvement was higher in indolent SM (100%) and smoldering SM (87.9%) compared to aggressive SM (46.8%) or mast cell leukemia (38.5%). After a median follow-up of 5.6 years no patient with CM had died, but 2.6% of the patients with MIS, 5.7% with SM+ and 28.95% with SM- had died. Overall survival was longer in patients with skin involvement (CM/MIS/SM+) compared to SM- patients (p<0.0001). These data argue for a thorough examination of both the skin and bone marrow in adult patients with mastocytosis.