October 2016




Signalment (JPC 3044519):  Dog, breed and age unspecified

HISTORY: Tissue from a firm, 3 x 4 cm skin mass at left paralumbar fossa

HISTOPATHOLOGIC DESCRIPTION:  Haired skin:  Infiltrating the subcutis, separating, surrounding and replacing skeletal muscle, and extending to cut borders, is an unencapsulated, well demarcated, infiltrative, densely cellular neoplasm composed of round to spindle cells arranged in broad sheets on a moderate fibrovascular stroma. Neoplastic cells have variably distinct cell borders, moderate to abundant eosinophilic finely fibrillar to occasionally microvacuolated cytoplasm, a round, oval, or reniform nucleus with finely stippled chromatin, and one distinct nucleolus. The mitotic count is regionally variable with up to 3 per 400x field. There is moderate anisocytosis and anisokaryosis.  Multifocally, there are moderate numbers of neoplastic multinucleated giant cells measuring up to 100 µm in diameter with up to 30 nuclei.  There is scattered single cell necrosis as well as large areas of coagulative necrosis with retention of cellular architecture and loss of differential staining and numerous cholesterol clefts and eosinophilic and cellular debris. Multifocally there are hemosiderin-laden macrophages and cholesterol clefts.  Multifocally, moderate numbers of myofibers are deeply eosinophilic, rounded, shrunken, with loss of cross striations (atrophy) and rarely fragmented (necrosis). 

MORPHOLOGIC DIAGNOSIS:  Haired skin: Cutaneous histiocytic sarcoma, breed not specified, canine


Signalment (JPC 1918993):  Cat, breed and age unspecified

HISTORY:  Tissue from a multilobulated mass in the lumbar region

HISTOPATHOLOGIC DESCRIPTION:  Haired skin and subcutis:  Infiltrating the subcutis and deep dermis, elevating the epidermis, and extending to cut borders, is an unencapsulated, densely cellular, multilobulated neoplasm composed of spindle cells arranged in long, interlacing streams and bundles on a moderate fibrovascular stroma; lobules are separated by broad bands of mature collagen. Neoplastic cells have indistinct borders and moderate amounts of eosinophilic, fibrillar cytoplasm.  Nuclei are elongate with finely stippled chromatin and have 1-2 variably distinct nucleoli. There is mild anisocytosis and anisokaryosis. Admixed with spindle cells are moderate numbers of more round, pleomorphic, multinucleated giant cells (up to 100um in diameter) with up to 10 nuclei and often prominent nucleoli. The mitotic count averages 3 per 10-400x fields.  Neoplastic cells surround a large, focally extensive area of drop-out and necrosis.  Multifocally within the neoplasm there are small areas of lytic necrosis with eosinophilic and cellular debris and hemorrhage. At the periphery of the neoplasm, often perivascularly, there are aggregates of lymphocytes with fewer plasma cells. The surrounding connective tissue and dermis are loosely arranged and expanded by clear space, with mildly ectatic lymphatics (edema). 

MORPHOLOGIC DIAGNOSIS:  Haired skin and subcutis:  Undifferentiated pleomorphic sarcoma, (previously known as malignant fibrous histiocytoma), breed not specified, feline

SYNONYMS:  Malignant fibrous histiocytoma, malignant giant cell tumor of soft parts, extraskeletal giant cell tumors, dermatofibrosarcomas, anaplastic sarcoma with giant cells



Localized histiocytic sarcoma

Feline progressive histiocytosis


Localized histiocytic sarcoma

Feline progressive histiocytosis


Localized histiocytic sarcoma

Feline progressive histiocytosis


Localized histiocytic sarcoma

 Feline progressive histiocytosis


Localized histiocytic sarcoma

Feline progressive histiocytosis


Localized histiocytic sarcoma

Feline progressive histiocytosis



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