Page 161 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

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Anaplastic sarcoma with giant cells and pleomorphic sarcoma
VetBooks.ir Group of poorly differentiated sarcomas characterized by the presence of multinucleated
giant cells. Also called undifferentiated pleomorphic sarcoma or malignant fibrous histiocy-
toma (MFH).

Clinical features
• Uncommon tumour with a reported incidence of less than 0.5% and 0.9% of all
cutaneous neoplasms in dogs and cats, respectively.
• Average age is 8 and 10 years in dogs and cats, respectively; however, lesions may be
seen in young animals.
• Females are more frequently affected than males (2:1).
• In dogs, it may arise in the skin as a single expansive lesion, or it may be part of a
multiorgan disease.
• In cats it is considered a variant of the vaccine-associated sarcoma but it may occur
also in non-vaccine sites.
• Solitary or multiple, variably sized, unencapsulated, poorly defined, subcutaneous
and dermal masses. In dogs, most tumour masses are located on extremities and
periarticular regions (e.g. elbow and stifle); in cats, the few cases described are located
on the extremities and abdomen, unless part of the injection site sarcoma complex.
• These tumours are locally infiltrative. Localized forms have a better prognosis if treated
early with wide surgical excision. Prognosis of disseminated forms is poor. Behavioural
differences may reflect the different cellular origin of these neoplasms.
• Over-represented canine breeds: Rottweiler, Golden Retriever and Flat-coated
Retriever.

Cytological features

• Cellularity is variable, often high.
• Background: clear to lightly basophilic and variably haemodiluted.
• Neoplastic cells are pleomorphic, often rounded to elongated and often exfoliate individually;
they may occasionally form poorly cohesive groups with a storiform arrangement.
• Nuclei are round to oval, often large, with coarse, granular or clumped chromatin. Multiple
prominent and irregularly shaped nucleoli are frequently seen.
• The cytoplasm is basophilic, moderate in amount and forms small cytoplasmic tails. It may
contain clear intracytoplasmic vacuoles.
• Large to very large multinucleated cells (up to 30 nuclei) are frequently seen in the sarcoma
with giant cells variant.
• Cytological features of atypia are often marked and include anisocytosis, anisokaryosis, vari-
ation in nucleus-to-cytoplasm ratio and often irregular mitotic figures.
Variants
Two main histological variants have been reported in the skin/subcutis of domestic animals. The
most relevant features of these variants can also be recognized on cytology.