Page 194 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

Round Cell Tumours
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10.4 Plasma Cell Tumour
VetBooks.ir Benign tumour of plasma cells, also known as plasmacytoma.

Clinical features
• Common cutaneous neoplasm of the dog, accounting for approximately 2% of all
canine skin tumours. Only rarely reported in the cat.
• It mostly occurs in older dogs, with an average age of approximately 10 years old.
• Small, single, slightly raised dermal nodules, covered by alopecic and occasionally
ulcerated skin. Multiple forms are rare but have also been reported in the absence of
multiple myeloma. These are referred to as cutaneous plasmacytosis.
• Pinnae and digits are the common locations but oral cavity may also be affected in
dogs. In cats, they have been documented on paws, thorax, face (lip, chin), neck,
shoulder, tail, metatarsus and nose.
• The clinical behaviour is usually benign in dogs. Recurrence after complete surgical
excision, metastases to distant skin sites and peripheral blood involvement have all
been reported on rare occasions.
• In cats, less is known about the clinical behaviour of this tumour, due to the paucity of
reported cases in the literature. For forms localized to the skin and/or regional lymph
node, surgical excision usually guarantees long-term disease control. Early progression to
systemic disease is reported in a few cases.
• Over-represented canine breeds: Yorkshire Terrier, Airedale Terrier, Kerry Blue Terrier,
Scottish Terrier, Cocker Spaniel and Standard Poodle.

Cytological features

• Cellularity is variable, often high.
• Background: clear or pale basophilic, variably haemodiluted.
• Plasma cells are round to oval with a moderate N:C ratio.
• Most of the time cells exfoliate individually, but occasionally they can form cluster-like
arrangements.
• Nuclei are generally round, occasionally oval and eccentric. The chromatin is uniform to
slightly clumped and nucleoli are indistinct.
• The cytoplasm is moderate to abundant and moderately to deeply basophilic. It may con-
tain a perinuclear clearing in the area of the Golgi zone. Russel bodies (inclusions contain-
ing immunoglobulin) may be found in some of the cells.
• Rarely, very fine needle-like inclusions (Auer-like bodies) or blue-black fine granules of iron
may be observed.
• Pleomorphism is variable and may be marked. Anisocytosis, anisokaryosis, bi- and/or multi-
nucleation can be marked. In these cases, neoplastic cells often lose their distinctive fea-
tures of typical plasma cells.
• Amyloid has been sporadically observed in a small percentage of well-differentiated plasma
cell tumours. Cytologically, amyloid appears as extracellular pink amorphous material,
which stains red–orange with Congo red. Amyloid can elicit a granulomatous inflamma-
tory response with multinucleated giant cells.
• Erythrophagocytosis by neoplastic plasma cells has rarely been reported.