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Mast Cell Neoplasia
Zachary M. Wright, DVM, DACVIM (Oncology)

VCA Animal Diagnostic Clinic, Dallas, TX, USA

Etiology/Pathophysiology older dogs, the author has seen numerous cases of MCT
in juveniles less than 1 year of age.
Mast cells are part of the normal canine, feline, and
human immune system. They primarily exist throughout History and Clinical Signs
the skin, lungs, and intestinal tract but are rarely found
within peripheral blood. Most dogs with a MCT present with a single dermal lesion.
Mast cells arise from pluripotent hematopoietic stem Twenty percent of all dogs, and specifically breeds that are
cells of the bone marrow. Once mature, their cytoplasm predisposed, may present with multiple tumors. The his-
contains a large amount of metachromatic granules. tory may include a nonpainful mass that increases and
These granules contain a variety of substances including decreases in size. Physical manipulation of the tumor can
histamine, serotonin, platelet activating factor, eosino- result in a rapid increase in size due to traumatic local
philic chemotactic factor, and heparin, among others. release of histamine (degranulation). Darier’s sign is the
In addition, mast cells produce a variety of cytokines that dermatologic description of wheal formation, local ery-
include interleukin (IL)‐1, IL‐3, IL‐4, IL‐5, IL‐6, and thema, and/or bruising secondary to manipulation of the
tumor necrosis factor (TNF)‐alpha. tumor. Most MCTs are clinically quiescent and are discov-
The etiology for canine mast cell tumor development ered on routine physical exam by the veterinarian or owner.
is unknown partially because there is no clear human Mast cell tumors occur predominantly in the dermis
model to provide key predictors. and are most commonly noted on the trunk and limbs.
A less commonly noted form, at mucocutaneous sites
(mouth, nasal planum, perirectal region), tends to have
Canine Mast Cell Neoplasia a more aggressive clinical behavior (Figure 155.1).

Additionally, a lesser percentage of MCTs occur in the
Epidemiology subcutaneous tissue and many have a clinical appear-
Canine mast cell tumor (MCT) is the most common skin ance consistent with a lipoma.
tumor in dogs, representing upwards of 15–20% of all Primary visceral mastocytosis is a very rare condition
skin tumors. They are one of the most common tumors in dogs. The disease has a predisposition for the intestinal
seen in practice. tract in older (>8 years) miniature‐breed dogs. Two inde-
pendent studies have identified the Maltese breed as hav-
Signalment ing a predisposition to the intestinal form. Clinical signs
are typical of most primary gastrointestinal pathology.
Mast cell tumor development has clear breed predisposi-
tions that include most brachycephalic breeds (boxer,
Boston terrier, and pug), Labrador and golden retrievers, Diagnosis
pit bull terriers, and shar‐peis. There is no reported sex Cytology of the lesion is diagnostic for a MCT. Because
predilection and the mean age of diagnosis is 8.2 years. of the clinical inefficiency and additional cost, pre-
Clinically, all breeds are capable of developing MCT. medication with an antihistamine prior to fine needle
While tumors are more often noted in middle‐aged to aspiration of a simple dermal mass less than 5 cm in

Clinical Small Animal Internal Medicine Volume II, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical