Mastocytosis: Overview

Approved by the Cancer.Net Editorial Board, 05/2014

ON THIS PAGE: You will find some basic information about this disorder, which may or may not become cancerous, and the parts of the body it may affect. This is the first page of Cancer.Net’s Guide to Mastocytosis. To see other pages, use the menu on the side of your screen. Think of that menu as a roadmap to this full guide.

Mastocytosis is a term that describes a group of disorders that are caused by 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 increase along with some non-cancerous (benign) conditions. Sometimes, certain types of cancers may begin from the growth of abnormal mast cells.

There are two general forms of mastocytosis: cutaneous, which involves the skin, and systemic, which involves the entire body.

Cutaneous mastocytosis

Cutaneous mastocytosis is an increase of mast cells in the skin. About 90% of people with mastocytosis have the cutaneous type. Subtypes of cutaneous mastocytosis include:

Urticaria pigmentosa. The most common form of cutaneous mastocytosis is urticaria pigmentosa. Tan or red-brown spots on the skin are the main sign of urticaria pigmentosa. These spots generally appear on the midsection of the body at first and then spread throughout the body. A person with this type of mastocytosis may also have nausea, vomiting, and diarrhea.

Solitary mastocytoma. This type of mastocytosis is more common in infants and children than in adults. It usually forms a large nodule on an arm or leg about 3 centimeters (cm) to 4 cm in diameter. 

Diffuse erythrodermic mastocytosis. Found most commonly in children younger than three years old, diffuse erythrodermic mastocytosis may not be noticeable when a child is born, but it can later show up as a rapid thickening of the skin. Symptoms of systemic mastocytosis (see below) and blisters are also common.

Telangiectasia macularis eruptiva perstans. This type of cutaneous mastocytosis develops mainly in adults. The most common sign is 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. Lymph nodes are tiny, bean-shaped organs that help fight infection. In 85% of people with systemic mastocytosis, urticaria pigmentosa (see above) develops first. The risk of developing systemic mastocytosis increases with age. Depending on the number of mast cells in an organ, it is classified as either indolent (slow-growing) or aggressive (fast-growing) mastocytosis. As the number of mast cells builds up in an organ, the symptoms of the disease may get worse.

Systemic mastocytosis can become 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 body’s soft tissues.

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