Mastocytosis is a rare neoplasm characterized by the expansion and accumulation of mast cells in various organ systems. Systemic mastocytosis (SM) may or may not present with cutaneous lesions. To examine the frequency and clinical impact of cutaneous involvement, data on 1,510 patients with mastocytosis collected in the registry of the European Competence Network on Mastocytosis were analyzed. Cutaneous involvement was found in 1,195 of 1,510 patients (79.1%). Of these, 286 had cutaneous mastocytosis, and 721 had SM with skin involvement. Adult patients with skin involvement who did not have a bone marrow examination (n = 188) were defined as having mastocytosis in the skin. In 315 patients, SM without skin involvement was found. 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 cutaneous mastocytosis had died, but 2.6% of the patients with mastocytosis in the skin, 5.7% of the patients with SM with skin involvement, and 28.95% of the patients with SM without skin involvement had died. Overall survival was longer in patients with skin involvement (cutaneous mastocytosis and/or mastocytosis in the skin and/or SM with skin involvement) than in patients with SM without skin involvement (P < 0.0001). These data argue for a thorough examination of both the skin and bone marrow in adult patients with mastocytosis.

Allergy Unit Verona University Hospital Verona Italy

CEITEC and University Hospital Brno Czech Republic

Department of Allergology Medical University of Gdańsk Gdańsk Poland

Department of Allergology University Medical Center Groningen University of Groningen Groningen The Netherlands

Department of Dermatology and Allergology Biederstein School of Medicine Technical University of Munich Munich Germany

Department of Dermatology and Venereology Medical University of Graz Graz Austria

Department of Dermatology University of Cologne Cologne Germany

Department of Dermatology Venereology and Allergology Medical University of Gdańsk Gdańsk Poland

Department of Hematology and Oncology University Hospital Mannheim Heidelberg University Mannheim Germany

Department of Hematology Hemostaseology Oncology and Stem Cell Transplantation University Hospital RWTH Aachen Aachen Germany

Department of Hematology Oncology and Stem Cell Transplantation Medical Center Faculty of Medicine University of Freiburg Freiburg Germany; Department of Hematology and Oncology Medical Center University of Schleswig Holstein Campus Lübeck Lübeck Germany

Department of Hematology University Medical Center Groningen University of Groningen Groningen The Netherlands

Department of Hematology University Medical Center Groningen University of Groningen Groningen The Netherlands; Department of Allergology University Medical Center Groningen University of Groningen Groningen The Netherlands

Department of Immunology Allergology Rheumatology Faculty of Medicine and Health Sciences Antwerp University Hospital University of Antwerp and University Hospital Antwerp Belgium

Department of Internal Medicine 1 Division of Hematology and Hemostaseology Medical University of Vienna Vienna Austria; Ludwig Boltzmann Institute for Hematology and Oncology Medical University of Vienna Vienna Austria

Department of Internal Medicine 1 Division of Hematology and Hemostaseology Medical University of Vienna Vienna Austria; Ludwig Boltzmann Institute for Hematology and Oncology Medical University of Vienna Vienna Austria; Department Hospital for Companion Animals and Horses University Clinic for Small Animals Internal Medicine Small Animals University of Veterinary Medicine Vienna Austria

Department of Internal Medicine 3 Hematology and Oncology University Hospital Johannes Kepler University Linz Austria

Department of Internal Medicine 4 Oncology Hematology Hemostaseology University Halle Germany

Department of Molecular Medicine University of Pavia Pavia Italy; Department of Hematology and Oncology University of Pavia Pavia Italy

Department of Molecular Medicine University of Pavia Pavia Italy; Department of Hematology and Oncology University of Pavia Pavia Italy; Fondazione IRCCS Policlinico San Matteo Pavia Italy

Division of Allergy and Clinical Immunology Department of Medicine University of Salerno Salerno Italy

Division of Allergy Department of Dermatology University of Basel Basel Switzerland; Department of Dermatology University of Cologne Cologne Germany

Division of Hematology Department of Medicine Stanford University School of Medicine Stanford California USA

Hematology Unit Verona University Hospital Verona Italy

Institute for Medical Informatics Statistics and Documentation Medical University of Graz Graz Austria

Pediatric Dermatology Unit Department of Medicine University of Padova Padova Italy

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