Faecal Occult Blood Test

Case of the Month (Emma Scurrell May 2012)

Extraskeletal osteosarcoma in a dog

A 1-year-old male neutered Dalmatian presented with a firm 4x3x3cm subcuticular mass overlying the right chest wall. There was no clinical or radiological association of the mass with the underlying ribs and no other lesions were found. A fine needle aspirate was performed and following the results, the mass was surgically resected and submitted for histopathology.

 Fig 1. Cytology of the subcuticular mass reveals large pleomorphic spindeloid to polygonal neoplastic cells (modified Wright’s stain, x 400). The cytological diagnosis was a malignant neoplasm, consistent with a sarcoma. 

Fig 2. Some of the cells contain pink intracytoplasmic granules such as in this cell near the centre of the image. These pink granules are not specific to osteosarcoma and can also be seen in chondrosarcomas and less commonly in other sarcomas (modified Wright’s stain, x 400).


Fig 3. Histopathology confirms the presence of a highly cellular infiltrative neoplasm composed of pleomorphic spindeloid to polygonal cells. Separating the neoplastic cells are seams of a bright pink matrix which is typical of osteoid and typical of an osteosarcoma. Mitotic figures can be seen at the 7 o’clock and 9 o’clock position in the image.  

Final Diagnosis

Extraskeletal osteosarcoma


The presence of a solitary subcuticular neoplasm in the absence of primary bone involvement is typical of an extraskeletal osteosarcoma. The majority of reported extraskeletal osteosarcomas are in the mammary gland and other sites less frequently involved include the subcutaneous tissue, liver, spleen, thyroid gland, intestinal tract, eye and muscle. Oesophageal osteosarcomas in association with Spirocerca lupi infection in dogs is a well-recognised phenomenon. Unfortunately, similar to primary bone osteosarcomas, the risk of metastasis is high.

Previous Monthly Cases

Hypertensive Retinopathy January 2010
FIP in a cat - uncommon presentation February 2010
Phaeohyphomycosis    March 2010 
Scleral Rupture April 2010
Canine and feline epulides May 2010
Erythema multiforme in a labrador retreiver June 2010
Keloidal fibrosarcoma in a labrador retreiver July 2010
Cutaneous epitheliotropic lymphoma  August 2010 
Benign cutaneous histiocytoma  September 2010 
Iridociliary adenoma October 2010
Proliferative thrombovascular necrosis of the pinnae November 2010
Signet-ring cell carcinoma in the stomach of a dog December 2010
Cutaneous infiltrative lipoma in a labrador January 2011

Tonsillar squamous cell carcinoma February 2011
Canine orbital meningioma March 2011
"Lung-digit" syndrome in a cat April 2011
Hepatic amyloidosis in a cat May 2011
Haemophagocytic histiocytic sarcoma June 2011
Alternaria spp. infection in an immunocompromised dog July 2011
Ocular manifestation of lymphoma in a cat  August 2011
Kerion dermatophytosis in a Cocker spaniel September 2011
Subcuticular coenurus in a rabbit  October 2011
Optic nerve glioma in a dog November 2011
Malignant transformation of a viral papilloma in a dog  December 2011
Uveodermatological syndrome in an Akita
January 2012
Cutaneous angiostomatosis in a dog  February 2012
Transitional cell carcinoma in a dog  March 2012
Corneal inclusion cysts in a dog   April 2012

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Faecal Occult Blood Test