• (systemic mastocytosis) A rare disease in which too many mast cells (a type of immune system cell) are found in the skin, bones, joints, lymph nodes, liver, spleen, and gastrointestinal tract. Mast cells give off chemicals such as histamine that can cause flushing (a hot, red face), itching, abdominal cramps, muscle pain, nausea, vomiting, diarrhea, low blood pressure, and shock.
  NCI Dictionary of Cancer Terms
  U.S. National Cancer Institute, 2021
• (systemic mastocytosis) Systemic infiltration of extracutaneous sites by clonal mast cells, with or without evidence of skin involvement.
  NCI
  U.S. National Cancer Institute, 2021
• A group of disorders caused by the abnormal proliferation of MAST CELLS in a variety of extracutaneous tissues including bone marrow, liver, spleen, lymph nodes, and gastrointestinal tract. Systemic mastocytosis is commonly seen in adults. These diseases are categorized on the basis of clinical features, pathologic findings, and prognosis.
  NLM Medical Subject Headings
  U.S. National Library of Medicine, 2025
• Systemic mastocytosis, often termed systemic mast cell disease (SMCD), is a heterogeneous clonal disorder of the mast cell and its precursor cells. It is now classified as a myeloproliferative neoplasm (MPN) as per the 2008 revision of the WHO classification of myeloid neoplasms.
  Medscape
  WebMD, 2025
• Systemic mastocytosis (mas-to-sy-TOE-sis) is a disorder that results in an excessive number of mast cells in your body. Mast cells normally help protect you from disease and aid in wound healing by releasing substances such as histamine and leukotrienes.
  Mayo Clinic
  Mayo Foundation for Medical Education and Research, 2025
• Systemic mastocytosis (SM) is a form of mastocytosis in which mast cells accumulate in internal tissues and organs such as the liver, spleen, bone marrow, and small intestines. It is typically diagnosed in adults. Signs and symptoms vary based on which parts of the body are affected. The disorder is usually caused by somatic changes...
  NIH Genetic and Rare Diseases
  National Center for Advancing Translational Sciences