mastocytoma
Meaning of mastocytoma: Rubbing one makes it swell, redden and itch within minutes, a response distinctive enough to identify the lesion without a biopsy.
Definition of mastocytoma
A mastocytoma is a localized growth built from mast cells, the tissue-dwelling immune cells that store histamine and release it when disturbed. In people it usually appears as a single tan or yellowish patch or nodule on the skin of an infant, which swells and reddens when rubbed. The same word names a far more serious tumor in dogs, where it is a common skin cancer.
What is a mast cell?
A sentinel cell packed with granules of histamine and other stored chemicals, sitting in the skin, the lining of the airways and gut, and around blood vessels. It is born in the bone marrow but finishes maturing only after it settles into tissue, so it is not a cell normally found circulating in blood. When it is triggered, whether by an allergen, a physical knock or heat, it empties its granules within seconds. That release produces the itch, redness and swelling of a hive.
Why does rubbing it swell?
Because a mastocytoma is a dense pile of exactly those cells. Firm stroking of the lesion sets them off together, and within minutes the patch reddens, swells into a weal and itches. The response is consistent enough to have a name, the Darier sign, and it separates a mast cell lesion from an ordinary birthmark or mole without any test. A large release can spread beyond the skin, causing flushing, cramping or a drop in blood pressure, which is uncommon but is the reason these lesions are taken seriously in infants.
How do the mast cell disorders compare?
| Form | Extent | Usual course |
|---|---|---|
| Solitary mastocytoma | One skin lesion | Appears in infancy, usually fades by adolescence |
| Urticaria pigmentosa | Many small skin lesions | Also childhood onset, most settle with age |
| Systemic mastocytosis | Marrow, liver, spleen, gut | Persistent, mainly adult onset |
| Canine mast cell tumor | Skin and deeper tissue in dogs | Frequently malignant, graded and staged |
That last row explains a good deal of confused writing on the subject. Descriptions of mast cell tumors invading fat and muscle and spreading to nodes come from veterinary oncology, where the tumor is one of the commonest canine cancers. The human childhood lesion is a benign tumor in the ordinary sense of the word and behaves nothing like it.
Also known as
Used in a sentence
A solitary mastocytoma was noted on the trunk during the infant skin examination.
Good to know
Mast cells mature in tissue rather than circulating in the bloodstream, and the solitary human mastocytoma is benign and usually resolves on its own, unlike the frequently malignant mast cell tumor seen in dogs.
Word origin
Where “mastocytoma” comes from
The ending combines Greek kytos, a vessel and later a cell, with -oma, a swelling or tumor. The mast- element comes from German Mastzelle, well-fed cell, named for granules that made the cells look stuffed with food.