Foot Mass - Soft Tissue Sarcoma
Foot Mass - Soft Tissue Sarcoma
Clinical Scenario
A 40-year-old male presents with a lump on his foot that he first noticed 6 months ago. It has been slowly increasing in size and has recently become mildly painful with weight-bearing. He has no significant past medical history and is an active builder.
History:
- 6-month history of slowly enlarging lump on dorsum of right foot
- Initially painless, now mild discomfort with weight-bearing
- No history of trauma
- No previous lumps or skin lesions
- No constitutional symptoms (weight loss, night sweats, fevers)
- Non-smoker, occasional alcohol
- Occupation: Builder (active work)
- No family history of cancer
Examination Findings:
- 5 x 4 cm firm, fixed mass on dorsolateral aspect of right midfoot
- Located deep to extensor tendons
- Not attached to overlying skin
- Fixed to underlying structures (does not move with tendon excursion)
- Non-tender
- No overlying skin changes (no ulceration, no satellite nodules)
- Normal pulses distally
- Intact sensation
- Full active range of motion of ankle and toes
- No regional lymphadenopathy (inguinal nodes impalpable)
Investigations
Laboratory Results
Imaging
Plain X-ray Right Foot:
- Soft tissue mass visible on dorsum of foot
- No calcification within the mass
- No underlying bone erosion or periosteal reaction
- No obvious bone involvement
- Normal bone density
MRI Right Foot with Gadolinium:
- 5.2 x 4.5 x 3.8 cm heterogeneous soft tissue mass
- Located deep to extensor digitorum brevis, superficial to tarsal bones
- T1: Intermediate signal, iso-intense to muscle
- T2: Heterogeneous high signal with some areas of low signal (haemorrhage or necrosis)
- Gadolinium: Heterogeneous enhancement with central non-enhancing areas (necrosis)
- Margins appear well-defined but no true capsule
- Abuts but does not invade underlying cuneiform and cuboid
- Displaces but does not encase dorsalis pedis artery
- No skip lesions
- No involvement of plantar structures
CT Chest:
- No pulmonary metastases
- No mediastinal lymphadenopathy
Questions & Model Answers
What is your differential diagnosis for this foot mass, and what features are concerning for malignancy?
Describe the principles of biopsy for a suspected soft tissue sarcoma, referencing Mankin's study.
The biopsy confirms high-grade undifferentiated pleomorphic sarcoma (UPS). How do you stage this tumour?
What are the surgical options for this patient? Discuss limb salvage versus amputation.
What is the role of radiotherapy and chemotherapy in soft tissue sarcoma?
What is the prognosis for this patient and what is the surveillance protocol?
Key Teaching Points
| Concept | Detail |
|---|---|
| Red Flags | Deep + >5cm + enlarging = treat as sarcoma |
| Biopsy | Mankin's principles - by treating surgeon, longitudinal, excisable tract |
| Staging | CT Chest essential - lungs are primary met site |
| Margins | Wide (1-2cm) for R0 resection |
| Radiotherapy | Reduces local recurrence from 50% to 15% |
| Chemotherapy | Less effective than in bone sarcomas |
Common Examiner Follow-up Questions
-
"What is the FNCLCC grading system?"
- French Fédération Nationale des Centres de Lutte Contre le Cancer
- Based on: Differentiation (1-3) + Mitoses (1-3) + Necrosis (0-2)
- Total 2-3 = Grade 1, 4-5 = Grade 2, 6-8 = Grade 3
- Higher grade = higher metastatic risk
-
"What is clear cell sarcoma?"
- "Melanoma of soft parts"
- Predilection for tendons and aponeuroses in foot/ankle
- EWSR1-ATF1 translocation
- S100 and HMB45 positive (like melanoma)
- Very aggressive, poor prognosis
-
"When would you resect pulmonary metastases?"
- Solitary or limited number (<3)
- Long disease-free interval (>12 months)
- Primary tumour controlled
- Patient fit for thoracic surgery
- Potentially curative if R0 resection achieved