Soft tissue sarcoma in dogs: biopsy and margins
9-year-old Labrador with a 4 cm subcutaneous mass on the lateral thigh, firm, fixed to deep tissues and growing over the last 2 months. Fine-needle aspiration yields scant spindle cells.
What is the most appropriate plan?
chevron_right Show answer and explanation
A. Shell out the mass, since it has a well-defined capsule that separates easily
It is a pseudocapsule made of compressed tumour cells. Shelling it out leaves microscopic disease and greatly increases local recurrence.
B. Chemotherapy as initial treatment to shrink the mass
Soft tissue sarcomas respond poorly to chemotherapy; local control with surgery (± radiotherapy) is the main treatment.
C. Incisional biopsy for grade, staging and surgery with 2–3 cm lateral margins and one deep fascial plane
Correct. Knowing the diagnosis and grade before surgery allows the definitive operation to be planned. If margins are incomplete, the options are re-excision or adjuvant radiotherapy.
D. Cytology with scant spindle cells rules out a tumour: monitoring is enough
Sarcomas exfoliate poorly; a poorly cellular sample does not rule out neoplasia. A firm, fixed, growing mass needs a histological diagnosis.
lightbulb Key takeaway
With any firm, undiagnosed subcutaneous mass, perform cytology and, if inconclusive, a biopsy before surgery: the first surgery has the best chance of cure. Histological grade guides the risk of metastasis and the need for adjuvant treatment.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.