Overview

Mastocytosis is a term that describes a group of disorders that are caused by the presence of too many mast cells in the body. A mast cell is a type of blood cell made in the bone marrow that is involved in allergic reactions and fighting parasitic infections. Mast cells produce histamine, a chemical that can cause itching, sneezing, congestion, swelling, and wheezing. Mast cells can be increased in association with some non-cancerous (benign) conditions. Sometimes, certain types of cancers may result from the growth of abnormal mast cells.

There are two general forms of mastocytosis: cutaneous and systemic.

Cutaneous mastocytosis

Cutaneous mastocytosis is an increase of mast cells in the skin and accounts for about 90% of mastocytosis cases. Subtypes of cutaneous mastocytosis include:

• Urticaria pigmentosa. The most common form of cutaneous mastocytosis is urticaria pigmentosa. It is characterized by tan or red-brown spots (lesions) on the skin. These spots generally appear first on the midsection of the body, and then can spread throughout the body. Symptoms such as nausea, vomiting, and diarrhea may also be present with urticaria pigmentosa.
  
  
• Solitary mastocytoma. More common in infants and children than in adults, this type usually forms a large nodule (3 centimeters (cm) to 4 cm in diameter) on the arm or leg.
  
  
• Diffuse erythrodermic mastocytosis. Found most commonly in children younger than three years old, diffuse erythrodermic mastocytosis may not be apparent at birth, but can later appear as rapid thickening of the skin. Symptoms of systemic mastocytosis (see below) and blisters are common.
  
  
• Telangiectasia macularis eruptiva perstans. This type of cutaneous mastocytosis is found mostly in adults. It is characterized by lesions that do not itch and are smaller than those of urticaria pigmentosa (see above).

Systemic mastocytosis

Systemic mastocytosis involves internal organs throughout the body, including the gastrointestinal tract, bone marrow, liver, spleen, and lymph nodes. In 85% of people with systemic mastocytosis, the cutaneous mastocytosis subtype of urticaria pigmentosa developed first. The risk of developing systemic mastocytosis increases with age. Depending on the number of mast cells in the different organ parts, it is classified as either indolent (slow-growing) or aggressive mastocytosis. As the number of mast cells build up in an organ, symptoms of the disease worsen.

Systemic mastocytosis can turn malignant (cancerous). The risk of systemic mastocytosis becoming cancerous is 7% when the disease begins in childhood and as much as 30% in adults. Mast cell leukemia involves the blood, while mast cell sarcoma involves the soft tissues.

Find out more about basic cancer terms used in this section.