CHAPTER 33 MAST CELL TUMORS 495
Predominant breeds: boxer, Staffordshire bull terrier, bulldog, English bulldog,
dachshund, Boston terrier, shar pei, basset hound, weimaraner, fox terrier, beagle,
pug, Labrador retriever, and golden retriever.Siamese cats: predisposed to histiocytic cutaneous mast cell tumors (young cats); may
resolve spontaneously.
Himalayan cats predisposed to urticaria pigmentosa (benign proliferative mast cell
disorder seen in young cats).
Dogs: mean age, 8 years; no sex predilection.
Cats: mean age, 10 years except for urticaria pigmentosa and histiocytic cutaneous
mast cell tumors; male predilection.
Reported in animals<1 year old and in cats as old as 18 years.
Dogs
Patient may have had skin or subcutaneous tumor for days to months at the time of
examination.
May have appeared to fluctuate in size.
Recent rapid growth after months of quiescence common.
Recent onset of erythema and edema most common with high-grade skin and subcu-
taneous tumors.
Cats
Often no demonstration of systemic signs.
Anorexia: most common complaint with splenic tumor.
Vomiting: may occur secondary to both splenic and gastrointestinal tumors.
CLINICAL FEATURES
Darier’s sign: mechanical manipulation or extreme changes in temperature can lead to
degranulation of mast cells with subsequent erythema and wheal formation and gas-
trointestinal ulceration causing anorexia, vomiting, and melena (Figures 33.1, 33.2).Dogs
Presentation extremely variable; may resemble any other type of skin or subcutaneous
tumor (benign and malignant); may resemble an insect bite or allergic reaction, sub-
cutaneous form may be mistaken clinically for a lipoma.Well-differentiated tumors: often slow growing; usually<3–4 cm in diameter; no
ulceration of overlying skin; variably alopecic; commonly present for more than 6
months (Figures 33.3–33.5).Poorly differentiated mast cell tumors: rapidly growing; variably sized; variable ulcer-
ation of the overlying skin and inflammation/edema of the surrounding tissue; rarely
present for more than 2–3 months prior to presentation (Figures 33.6, 33.7).Primarily a solitary skin or subcutaneous mass, but may be multifocal (Figure 33.8).