Page 187 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

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10.2 Feline Mast Cell Tumour (Feline MCT)

VetBooks.ir Neoplasia of mast cells.

Clinical features
• Common neoplasm accounting for approximately 7% and 21% of all feline skin
tumours, according to previous European and American studies, respectively. Vis-
ceral forms are much more common than in dogs and account for up to 50% of all
feline mast cell tumours (MCTs).
• Age: adult cats are more frequently affected, with an average of approximately 10 years.
However, it can be observed in cats of any age. No sex predisposition reported.
• It can develop anywhere in the body, with preference for head (especially in young
animals), neck, trunk and legs.
• It usually presents as a single firm tan papule, plaque or discrete nodule in the skin
or subcutis. Overlying epidermis is usually pink and alopecic, but it may be ulcerated.
Approximately 20% of cats present with multiple lesions.
• Mastocytaemia is uncommon.
• Cutaneous mast cell tumour is generally a benign neoplasm in cats, but up to 22% of
cases may show an aggressive behaviour.
• Over-represented feline breeds: Siamese, Burmese, Russian Blue, Ragdoll, Maine
Coon, Oriental and Havana cat.

Cytological features

• Cellularity is variable, often high.
• Background: often clear, variably haemodiluted. It often contains free purple granules derived
from the disruption of the mast cells during the smearing.
• Neoplastic mast cells are round with a moderate N:C ratio.
• Nuclei are often obscured by the granules. When visible, they are round to oval, mostly par-
acentral, with uniform to slightly clumped chromatin and variably visible nucleoli.
• The cytoplasm is clear or lightly basophilic, moderate to abundant and commonly contains
numerous fine purple/magenta granules. Granules are often finer than in dogs. In poorly
granulated forms, granules may be present in very low numbers and/or may have a patchy
distribution.
• Cytological pleomorphism is variable and is more prominent in the pleomorphic variant.
Anisocytosis and anisokaryosis can be moderate to marked and binucleation and/or multi-
nucleation are often observed. Mitotic figures can be seen in variable numbers.
• Occasionally, neoplastic cells can display erythrophagia.
• Eosinophils are also present, but with a lower frequency than in canine MCT. Low numbers
of small lymphocytes can also be observed.
• Reactive fibroblasts and collagen fibrils are rarely present.
Variants
Histologically, feline MCTs can be subclassified in different forms. In the literature, the termin-
ology is not standardized and there is inconsistency between studies. The following is the
classification of feline cutaneous MCTs suggested by Kiupel (2016) in the latest edition of
Meuten’s Tumors in Domestic Animals.