CONDITION

Soft Tissue Sarcomas

Why this matters now

Soft tissue sarcomas most commonly develop in middle-aged to older animals, though they can occur at any age. In cats, there may be associations with previous injections at certain sites (injection-site sarcomas), which has influenced vaccination and injection practices. The tumours typically grow slowly at first, which may delay recognition.

These tumours often begin as small, firm lumps beneath the skin that gradually enlarge over weeks to months. The growth rate can vary considerably between tumour types and individual cases. Soft tissue sarcomas characteristically send microscopic extensions into surrounding normal tissue, making them difficult to remove completely. Without adequate treatment, local recurrence is common. Spread to other organs occurs less frequently than with some other malignancies but becomes more likely with higher-grade tumours.

Signals & patterns

Early signals

Firm, subcutaneous lump

A mass felt beneath the skin that may be attached to underlying structures or relatively mobile.

Gradual increase in size

Slow but progressive growth over weeks to months, though rate varies considerably.

Lump appears in limb, trunk, or head/neck

Common locations include legs, flank, chest wall, and head regions.

Mass may feel smooth or irregular

Surface characteristics vary depending on tumour type and location.

Later signals

More rapid growth

Acceleration in growth rate may occur, with the mass becoming more obvious.

Ulceration or surface changes

Larger tumours may outgrow their blood supply, leading to skin breakdown.

Reduced mobility or lameness

Masses affecting limbs may interfere with movement as they enlarge.

Signs of systemic illness

Advanced or metastatic disease may cause weight loss, reduced appetite, or lethargy.

Click to read about the biological mechanisms

How this is usually investigated

Investigation aims to characterise the tumour type, assess its extent, and determine whether spread has occurred. This information guides treatment planning.

Fine needle aspirate

Purpose: To collect cells from the mass for initial microscopic assessment
Considerations: Can suggest sarcoma but often cannot provide complete tumour type or grade. Useful as a first step to guide further investigation.

Tissue biopsy

Purpose: To obtain a larger sample for definitive diagnosis and grading
Considerations: Provides information about tumour type and aggressiveness. Biopsy placement should consider potential future surgery to avoid spreading tumour cells.

Advanced imaging (CT or MRI)

Purpose: To assess tumour extent and plan surgical margins
Considerations: Particularly valuable for tumours in complex anatomical locations. Helps identify the true extent of tissue involvement.

Chest radiographs or CT

Purpose: To check for visible lung metastases
Considerations: Part of staging to assess whether spread has occurred. Absence of visible metastases does not guarantee absence of microscopic spread.

Regional lymph node assessment

Purpose: To evaluate whether tumour has spread to nearby lymph nodes
Considerations: Fine needle aspirate or biopsy of enlarged nodes helps determine staging and prognosis.

Options & trade-offs

Management typically involves surgery as the primary treatment, potentially combined with radiation therapy. The approach depends on tumour location, size, grade, and individual circumstances.

Wide surgical excision

Removal of the tumour with substantial margins of normal tissue in all directions.

Trade-offs: Aims to remove microscopic extensions. May require significant tissue removal. Location affects what margins are achievable. Amputation may be considered for limb tumours.

Radiation therapy

Use of targeted radiation to kill tumour cells, often used before or after surgery.

Trade-offs: Can improve local control, particularly when surgical margins are incomplete. Requires multiple treatment sessions. May cause localised side effects.

Chemotherapy

Systemic treatment that may be considered for high-grade tumours or metastatic disease.

Trade-offs: Role in soft tissue sarcomas is less established than for some other cancers. May be recommended in specific situations.

Palliative management

Focus on maintaining comfort and quality of life when curative treatment is not pursued.

Trade-offs: May be appropriate for extensive tumours, elderly animals, or when owners choose this approach. Can include pain management and supportive care.

Monitoring approach

Observation with regular reassessment for slow-growing, low-grade tumours in older animals.

Trade-offs: May be reasonable when the tumour is small and slow-growing, particularly if surgery would be challenging. Requires commitment to regular monitoring.

Common misconceptions

Misconception:

"A moveable lump cannot be a sarcoma"

Reality:

Whilst some sarcomas feel fixed to underlying structures, others can be relatively mobile on examination, particularly when small. The feel of a mass does not reliably predict its nature.

Misconception:

"If a lump has been present unchanged for a long time, it must be benign"

Reality:

Soft tissue sarcomas can grow slowly, particularly initially. A long duration does not exclude malignancy, and any growing mass warrants investigation.

Misconception:

"Simple removal is sufficient treatment"

Reality:

The invasive nature of soft tissue sarcomas means that surgical removal without adequate margins often leaves microscopic tumour cells behind, leading to regrowth.

Noting when the lump was first observed and whether it has changed in size provides useful timeline information. Photographing the mass and measuring it periodically can help track changes objectively. Considering the mass's exact location and whether it affects the animal's movement or comfort helps inform discussions about investigation and management options.

Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS