Malignant Smooth-Muscle Sarcoma | Spindle Cells with Blunt-Ended Nuclei | Grade and Size Drive Outcome
Clinical Subgroups by Site
Critical Must-Knows
- Leiomyosarcoma is a malignant tumour of smooth muscle and is one of the commonest adult soft tissue sarcomas
- Histology shows intersecting fascicles of spindle cells with blunt-ended (cigar-shaped) nuclei and eosinophilic cytoplasm
- Immunohistochemistry is positive for smooth-muscle markers - desmin, smooth muscle actin (SMA) and h-caldesmon
- Tumour grade (FNCLCC) and size are the dominant independent predictors of survival and distant recurrence
- Wide local excision is the curative treatment; chemotherapy is reserved for advanced or selected high-risk disease, not routine adjuvant use
Clinical Pearls
- "Soft tissue leiomyosarcoma is biologically different from GIST - it is NOT KIT/CD117 driven and does not respond to imatinib
- "Retroperitoneal location carries a worse prognosis than extremity disease, largely because of size and margin difficulty
- "Lung is the dominant site of distant metastasis for extremity tumours; liver is important for retroperitoneal and vascular tumours
- "Adjuvant chemotherapy did NOT improve survival in the EORTC 62931 randomised trial of resected soft tissue sarcoma
Clinical Imaging
Critical Leiomyosarcoma Exam Points
Smooth-Muscle Identity
Leiomyosarcoma is a malignant smooth-muscle tumour. Diagnosis rests on spindle cells with blunt-ended nuclei plus a smooth-muscle immunoprofile (desmin, SMA, h-caldesmon positive). It is NOT a GIST and does not respond to imatinib.
Grade and Size Rule Prognosis
FNCLCC grade and tumour size are the dominant independent predictors of survival and distant recurrence. Site (retroperitoneal versus extremity) matters mostly because retroperitoneal tumours are large and hard to resect with clear margins.
Surgery Is the Cure
Wide local excision with negative margins is the only reliable curative treatment. Radiotherapy improves local control for deep or larger extremity tumours. Chemotherapy is not routine adjuvant therapy.
Biopsy Before Excision
Image-guided core needle biopsy, planned with the definitive surgeon, comes before any excision. Never shell out (marginal excise) an undiagnosed deep soft tissue mass - it compromises later limb-salvage surgery.
SMOOTHLeiomyosarcoma Core Features
| S | Smooth-muscle origin Malignant tumour of smooth muscle (vessel walls, dermis, viscera) |
| M | Markers desmin/SMA/h-caldesmon Smooth-muscle immunoprofile confirms diagnosis |
| O | Older adults Peak 50-70 years, slight female predominance overall |
| O | Outcome by grade and size FNCLCC grade and size are dominant predictors |
| T | Three sites Extremity/trunk, retroperitoneal/abdominal, and vascular (e.g. IVC) |
| H | Haematogenous spread Lung (extremity) and liver (retroperitoneal/vascular); nodes rare |
| S | Smooth-muscle origin Malignant tumour of smooth muscle (vessel walls, dermis, viscera) | O | Older adults Peak 50-70 years, slight female predominance overall | T | Three sites Extremity/trunk, retroperitoneal/abdominal, and vascular (e.g. IVC) |
| M | Markers desmin/SMA/h-caldesmon Smooth-muscle immunoprofile confirms diagnosis | O | Outcome by grade and size FNCLCC grade and size are dominant predictors | H | Haematogenous spread Lung (extremity) and liver (retroperitoneal/vascular); nodes rare |
Hook:SMOOTH muscle gone bad - SMOOTH captures origin, markers, demographics, prognosis, sites and spread.
BEEFHistology Clues for Leiomyosarcoma
| B | Blunt-ended nuclei Cigar-shaped (not tapered) nuclei are the classic clue |
| E | Eosinophilic cytoplasm Brightly eosinophilic, fibrillary cytoplasm |
| E | Elongated fascicles intersecting at right angles Fascicles crossing at 90 degrees |
| F | Fibrillarity plus smooth-muscle markers Desmin, SMA, h-caldesmon confirm smooth-muscle line |
| B | Blunt-ended nuclei Cigar-shaped (not tapered) nuclei are the classic clue | E | Elongated fascicles intersecting at right angles Fascicles crossing at 90 degrees |
| E | Eosinophilic cytoplasm Brightly eosinophilic, fibrillary cytoplasm | F | Fibrillarity plus smooth-muscle markers Desmin, SMA, h-caldesmon confirm smooth-muscle line |
Hook:Think BEEF - smooth muscle is meat: blunt nuclei, eosinophilic cytoplasm, intersecting fascicles, fibrillary cytoplasm.
GRIMSAdverse Prognostic Factors
| G | Grade high (FNCLCC 3) High grade drives distant recurrence and death |
| R | Retroperitoneal / deep site Worse than superficial extremity disease |
| I | Incomplete (positive) margins Strongest driver of local recurrence |
| M | Measurement large (size over 5cm) Independent predictor of distant spread and mortality |
| S | Spread (metastatic at presentation) Stage IV markedly reduces survival |
| G | Grade high (FNCLCC 3) High grade drives distant recurrence and death | M | Measurement large (size over 5cm) Independent predictor of distant spread and mortality |
| R | Retroperitoneal / deep site Worse than superficial extremity disease | S | Spread (metastatic at presentation) Stage IV markedly reduces survival |
| I | Incomplete (positive) margins Strongest driver of local recurrence |
Hook:A GRIMS picture means a worse outcome - Grade, Retroperitoneal, Incomplete margins, Measurement large, Spread.
Overview and Epidemiology
Leiomyosarcoma is a malignant tumour that shows differentiation toward smooth muscle. It is one of the more common adult soft tissue sarcomas. In soft tissue, it arises wherever smooth muscle exists - in the walls of blood vessels, in the dermal arrector pili muscles, and from poorly differentiated mesenchymal cells. The three clinically important groups are somatic soft tissue tumours of the extremity and trunk, retroperitoneal and abdominal tumours, and tumours of large vessels such as the inferior vena cava.
Leiomyosarcoma Is Not GIST
Do not confuse soft tissue leiomyosarcoma with gastrointestinal stromal tumour (GIST). Historically many gut "leiomyosarcomas" were reclassified as GISTs once KIT/CD117 and DOG1 testing became available. True leiomyosarcoma is KIT-negative, is driven by smooth-muscle biology rather than KIT/PDGFRA mutations, and does not respond to imatinib. Modern leiomyosarcoma series deliberately exclude GISTs.
Demographics
- Age: Most patients are middle-aged to older adults (typically 50-70 years)
- Gender: Slight overall female predominance (strong in uterine disease)
- Share of sarcomas: Roughly 10-20% of adult soft tissue sarcomas
- Young patients: Uncommon but possible; consider in any persistent deep mass
Site Distribution
- Extremity / trunk: Common somatic soft tissue site, often deep
- Retroperitoneum / abdomen: Frequent and prognostically poor (large, hard margins)
- Vascular (IVC and other vessels): Distinct group arising from the vessel wall
- Cutaneous / subcutaneous: Smaller, better prognosis when superficial
Outcome by Site (MSKCC Primary Leiomyosarcoma Series)
| Site Group | Approximate Share | Recurrence Pattern | Prognostic Note |
|---|---|---|---|
| Extremity | About half of primary cases | Distant recurrence around one third | Best access to wide margins; favourable group |
| Abdominal / retroperitoneal | About 40% | Recurrence around half; late recurrence after 5 years | Worse disease-specific survival, driven by size and margins |
| Truncal | About 1 in 10 | Recurrence around one quarter | Intermediate behaviour |
Pathophysiology and Molecular Biology
Cellular Origin and Genetics
Leiomyosarcoma differentiates toward smooth muscle. Unlike synovial sarcoma or Ewing sarcoma, it has no single recurrent translocation. Instead it shows a complex karyotype with widespread chromosomal gains and losses and frequent inactivation of tumour-suppressor pathways. This genomic complexity is typical of the "non-translocation" pleomorphic sarcomas and explains why no targeted driver therapy (such as imatinib for GIST) exists.
Genomic Landscape
Complex, unstable genome:
- No pathognomonic fusion gene (contrast synovial sarcoma)
- Frequent loss of tumour-suppressor function (e.g. RB1 and TP53 pathways)
- Numerous copy-number changes and chromosomal rearrangements
- Heterogeneous biology between uterine and non-uterine tumours
Diagnostic Immunoprofile
Smooth-muscle markers establish the line of differentiation:
- Desmin: Commonly positive
- Smooth muscle actin (SMA): Commonly positive
- h-caldesmon: More specific smooth-muscle marker
- May show focal keratin or EMA - a recognised diagnostic trap
Diagnosis Is Morphology Plus Immunohistochemistry
There is no single confirmatory molecular test for leiomyosarcoma. Diagnosis combines characteristic histology (intersecting fascicles, blunt-ended nuclei, eosinophilic cytoplasm) with a smooth-muscle immunoprofile (desmin, SMA, h-caldesmon). Always exclude GIST (KIT/DOG1) for visceral lesions and exclude dedifferentiated liposarcoma with smooth-muscle areas in the retroperitoneum.
Tumour Biology and Behaviour
| Characteristic | Description | Clinical Implication |
|---|---|---|
| Growth | Enlarging deep mass, often painless until large | Diagnostic delay common; any deep mass over 5cm needs urgent imaging |
| Local behaviour | Infiltrative; pushes and invades along fascial planes | Wide margins essential to control local recurrence |
| Metastatic route | Predominantly haematogenous, lymph-node spread uncommon | Stage the lungs (and liver for retroperitoneal/vascular tumours) |
| Late recurrence | Recurrence can occur beyond 5 years, especially retroperitoneal | Long-term surveillance is mandatory |
Classification and Grading
Histological Diagnosis
Classic Histology
Leiomyosarcoma is built from intersecting fascicles of spindle cells that cross at roughly right angles.
Cellular Features
- Blunt-ended (cigar-shaped) nuclei - the classic clue
- Brightly eosinophilic, fibrillary cytoplasm
- Perinuclear vacuoles may be seen
- Mitoses present; atypia varies with grade
Architecture
- Long sweeping fascicles intersecting at 90 degrees
- Higher-grade tumours show pleomorphism and necrosis
- Pleomorphic / dedifferentiated areas in high-grade tumours
- Coagulative tumour necrosis contributes to grade
The combination of blunt-ended nuclei and eosinophilic cytoplasm in intersecting fascicles is the textbook appearance.
FNCLCC Histological Grading
Grade is the single most important histopathological prognostic factor in soft tissue sarcoma. The FNCLCC (French Federation of Cancer Centres) system assigns a grade from a score built on three components.
FNCLCC Grading Components
| Parameter | What Is Scored | Score Range |
|---|---|---|
| Tumour differentiation | How closely the tumour resembles normal adult mesenchymal tissue | 1 to 3 |
| Mitotic count | Mitoses per 10 high-power fields | 1 to 3 |
| Tumour necrosis | Extent of coagulative necrosis | 0 to 2 |
| Total score to grade | Sum of the three scores maps to grade | Grade 1, 2 or 3 |
Grade Drives Distant Recurrence
The total FNCLCC score (differentiation plus mitotic count plus necrosis) maps to grade 1, 2 or 3. High grade (grade 3) is independently associated with distant recurrence and death. In leiomyosarcoma specifically, grade and size are the dominant predictors of disease-specific survival.
AJCC Staging (Soft Tissue Sarcoma)
AJCC 8th Edition (Trunk and Extremity, simplified)
| Stage | Grade | Size / Spread | General Outlook |
|---|---|---|---|
| IA | Low (G1) | 5cm or less | Favourable |
| IB | Low (G1) | Greater than 5cm | Favourable |
| II | High (G2-3) | 5cm or less | Intermediate |
| IIIA / IIIB | High (G2-3) | Greater than 5cm (size bands) | Higher risk of distant relapse |
| IV | Any | Nodal or distant metastasis | Poor |
Retroperitoneal sarcomas use a separate AJCC size-banded staging scheme. Most clinically significant leiomyosarcomas are intermediate to high grade.
Clinical Presentation
History
Presenting Features
- Extremity/trunk: Enlarging, often painless deep mass
- Retroperitoneal: Vague abdominal fullness, pain, mass effect
- Vascular (IVC): Leg swelling, Budd-Chiari features, abdominal pain
- Cutaneous: Small firm dermal/subcutaneous nodule
Red Flags for Any Soft Tissue Mass
- Size greater than 5cm
- Deep to fascia
- Increasing in size
- New pain in a previously painless lump
Treat a Deep Mass as Sarcoma Until Proven Otherwise
Any soft tissue mass that is larger than 5cm, deep to fascia, or enlarging should be regarded as a sarcoma until proven otherwise and referred to a specialist sarcoma service. Reassuring slow growth does not exclude leiomyosarcoma.
Examination Approach
Clinical Assessment
- Mass size and relation to surface anatomy
- Skin changes (uncommon unless cutaneous or fungating)
- Limb swelling or venous engorgement (vascular tumours)
- Firm, often fixed deep mass
- Relation to neurovascular bundle
- Tenderness if large or nerve-involving
- Joint range of motion if periarticular
- Distal neurovascular status
- Muscle power in the affected compartment
- Regional nodes (metastasis uncommon but recorded)
- Respiratory assessment (lung is the dominant metastatic site)
A complete baseline supports later treatment planning.
Investigations and Imaging
Imaging Protocol
MRI (Gold Standard for Local Staging)
MRI of the whole anatomical region defines the tumour and its relations.
Protocol and findings:
- T1-weighted: anatomy and tumour extent
- T2-weighted with fat suppression: heterogeneous high signal
- Post-contrast T1 with fat suppression: heterogeneous enhancement, may show necrosis
- Define relation to neurovascular bundle, bone and compartment boundaries
MRI is essential before biopsy and surgery to plan margins and the biopsy tract.
Biopsy
Biopsy Principles
Core principles for any suspected soft tissue sarcoma:
- Image-guided core needle biopsy is the standard
- Plan the biopsy tract with the definitive surgeon so it can be excised en bloc
- Refer to a sarcoma centre before biopsy wherever possible
- Never perform an unplanned marginal ("shell-out") excision of an undiagnosed deep mass - it seeds tumour and jeopardises limb salvage
- Send tissue for full immunohistochemistry (desmin, SMA, h-caldesmon, plus KIT/DOG1 and MDM2/CDK4 where relevant)
Management
Core Principles
Surgery Is the Backbone of Cure
Wide local excision with negative margins is the only reliable curative treatment for localised leiomyosarcoma. Radiotherapy improves local control for deep or larger extremity tumours. Unlike synovial sarcoma, chemotherapy is not standard adjuvant therapy and is reserved for advanced or selected high-risk disease decided at a multidisciplinary meeting.
Treatment fundamentals:
- Surgery: wide excision with a cuff of normal tissue, biopsy tract excised en bloc
- Radiotherapy: pre- or post-operative for deep/larger extremity tumours or close margins
- Systemic therapy: doxorubicin-based regimens for advanced disease; not routine adjuvant
These principles apply across leiomyosarcoma sites, modified by anatomy.
Systemic Agents in Advanced Leiomyosarcoma
| Setting | Agent(s) | Evidence Summary |
|---|---|---|
| First line, advanced | Doxorubicin (anthracycline) based | Standard backbone for metastatic soft tissue sarcoma |
| After anthracycline failure | Trabectedin | Phase III: improved progression-free survival versus dacarbazine in leiomyosarcoma/liposarcoma |
| Pre-treated, advanced | Eribulin | Phase III: improved overall survival versus dacarbazine in this pooled leiomyosarcoma/liposarcoma population |
| Resected, localised | Adjuvant doxorubicin/ifosfamide | EORTC 62931: no relapse-free or overall survival benefit - not routine |
Surgical Technique
Preoperative Planning
Preparation Steps
- Review MRI/CT with radiology and the sarcoma MDT
- Define tumour extent and neurovascular relations
- Confirm diagnosis and grade on core biopsy
- Plan resection margins and reconstruction
- Mark the biopsy tract for en bloc excision
- Plan a longitudinal, extensile incision
- Treat drain sites as contaminated
- Anticipate the soft tissue defect
- Arrange flap or graft coverage if needed
- Plan vascular reconstruction for vessel-based tumours
Good planning underpins both oncological clearance and function.
Complications
Disease and Treatment Complications
| Complication | Driver | Management |
|---|---|---|
| Local recurrence | Positive margins, high grade, large size | Re-resection where feasible; radiotherapy |
| Distant metastasis | High grade, large size (lung dominant; liver for retroperitoneal/vascular) | Systemic therapy; metastasectomy for resectable oligometastatic lung disease |
| Wound complications | Pre-operative radiotherapy, poor soft tissue coverage | Wound care, negative-pressure therapy, flap coverage |
| Nerve / vascular deficit | Tumour proximity or deliberate sacrifice | Reconstruction, physiotherapy, orthotics |
| Chemotherapy toxicity | Anthracycline (cardiotoxicity), ifosfamide | Cumulative-dose limits, cardiac monitoring, supportive care |
Surveillance
Follow-up Strategy
Surveillance Schedule
- Clinical review every 3-4 months
- Chest CT for lung metastases
- Local MRI for high-grade or marginal-resection tumours
- Clinical review every 6 months
- Periodic chest imaging
- Local imaging guided by symptoms and risk
- Annual review
- Continue chest (and abdominal for retroperitoneal/vascular) imaging
- Late recurrence is recognised, especially in retroperitoneal disease
Surveillance Must Be Long
Leiomyosarcoma can recur late - distant or local recurrence beyond 5 years is well described, particularly for abdominal and retroperitoneal tumours. A written long-term surveillance plan is essential.
Prognosis and Outcomes
Prognostic Factors
| Factor | Favourable | Unfavourable |
|---|---|---|
| FNCLCC grade | Low grade (G1) | High grade (G3) |
| Size | 5cm or less | Greater than 5cm |
| Site | Extremity / superficial | Retroperitoneal / deep |
| Margin status | Negative | Positive |
| Stage | Localised | Metastatic at presentation |
Grade and Size Are the Independent Drivers
In primary leiomyosarcoma, multivariate analysis shows that grade and size are the dominant independent predictors of disease-specific survival and distant recurrence, while margin status drives local recurrence. Although retroperitoneal tumours do worse than extremity tumours, much of that difference is explained by their larger size and the difficulty of obtaining clear margins.
Controversies and Areas of Uncertainty
Adjuvant Chemotherapy
The benefit of adjuvant chemotherapy in resected soft tissue sarcoma remains unproven. The EORTC 62931 randomised trial of doxorubicin plus ifosfamide showed no relapse-free or overall survival benefit, so chemotherapy is not routine and is reserved for selected high-risk cases at MDT discretion.
Histology-Driven Systemic Therapy
Trabectedin and eribulin have specific activity in leiomyosarcoma and liposarcoma, supporting a move toward histology-specific second-line therapy rather than one-size-fits-all chemotherapy. The optimal sequencing of agents is still debated.
Role of Radiotherapy in Retroperitoneal Disease
Radiotherapy is well established for deep extremity sarcoma but its role in the retroperitoneum is contested, with trial data showing limited benefit. Use is selective and individualised.
Lung Metastasectomy
Resection of resectable, oligometastatic lung disease is widely practised and associated with longer survival in selected patients, but no randomised trial confirms a survival benefit. Patient selection is decisive.
Evidence Base and Key Studies
Predictors of Survival and Recurrence in Primary Leiomyosarcoma
- 353 patients with primary resectable leiomyosarcoma (GISTs excluded) from a prospective database, 1982-2006
- Distribution: 48% extremity, 41% abdominal/retroperitoneal, 11% truncal; 75% high grade, median size 6.0cm
- On multivariate analysis only high grade and size were independent predictors of disease-specific survival
- Late recurrence beyond 5 years occurred in 9% of abdominal/retroperitoneal and 4% of extremity tumours
Prognostic Factors in 1,041 Localised Extremity Soft Tissue Sarcomas
- 1,041 adults with localised extremity soft tissue sarcoma treated at a single institution, prospective data
- 5-year survival 76%; high grade, large size and deep location were adverse for disease-specific survival
- Leiomyosarcoma histology was an independent adverse factor for both distant recurrence and disease-specific survival
- Microscopically positive margins independently predicted local recurrence and tumour-related death
Histological Grading of Soft Tissue Sarcomas (FNCLCC and MIB-1)
- Reviews histological grading as the most important histopathological prognostic factor in soft tissue sarcoma
- Describes the FNCLCC system based on differentiation, mitotic count and tumour necrosis
- Discusses the MIB-1 (Ki-67) proliferation index as an adjunct to grading
- Highlights pitfalls in grade assessment and its relationship to other clinicopathological factors
Exam Viva Scenarios
Use these scenarios to practise clinical reasoning and management decisions
Scenario 1: Enlarging Thigh Mass in an Older Adult
"A 62-year-old man has a 7cm deep, firm, painless mass in the posterior thigh that has been slowly enlarging over six months. How would you investigate and manage him?"
Scenario 2: Retroperitoneal Leiomyosarcoma
"A 58-year-old woman has a 14cm retroperitoneal mass on CT. Core biopsy reports a high-grade spindle-cell tumour. How do you confirm the diagnosis and plan treatment, and how does this differ from an extremity tumour?"
Scenario 3: Metastatic Leiomyosarcoma
"A 55-year-old man treated two years ago for a high-grade extremity leiomyosarcoma now has three FDG-avid nodules confined to the right lung on surveillance CT. How do you proceed, and what systemic options exist if surgery is not appropriate?"
MCQ Practice Points
Diagnosis Question
Q: Which immunohistochemical profile confirms leiomyosarcoma? A: Positive for smooth-muscle markers - desmin, smooth muscle actin (SMA) and h-caldesmon - with characteristic spindle cells showing blunt-ended (cigar-shaped) nuclei. KIT/CD117 is negative, which helps exclude GIST.
Prognosis Question
Q: What are the dominant independent predictors of survival in primary soft tissue leiomyosarcoma? A: FNCLCC grade and tumour size. Margin status is the key driver of local recurrence. Retroperitoneal site is associated with worse outcome largely because of larger size and margin difficulty.
Treatment Question
Q: Is adjuvant chemotherapy standard after resection of localised leiomyosarcoma? A: No. The EORTC 62931 randomised trial of doxorubicin plus ifosfamide showed no relapse-free or overall survival benefit. Chemotherapy is reserved for advanced disease or individualised high-risk cases.
Distinction Question
Q: How does soft tissue leiomyosarcoma differ from GIST? A: Leiomyosarcoma is a true smooth-muscle tumour that is KIT-negative and does NOT respond to imatinib. GIST is KIT/DOG1 positive and is treated with imatinib. Many old gut "leiomyosarcomas" were reclassified as GISTs.
Metastasis Question
Q: What are the dominant metastatic sites in leiomyosarcoma? A: Lung for extremity tumours; liver is also important for retroperitoneal and vascular tumours. Spread is predominantly haematogenous and lymph-node metastasis is uncommon.
Guidelines, Registries & Global Practice
Global Epidemiology
Burden
- Share of sarcomas: Roughly 10-20% of adult soft tissue sarcomas worldwide
- Age: Predominantly middle-aged and older adults (typically 50-70 years)
- Sex: Slight overall female predominance, strongest in uterine disease
- Reclassification effect: True leiomyosarcoma figures rose in clarity once GISTs were separated out
Outcome Pattern
- Drivers: Grade and size dominate survival; margins drive local recurrence
- Site: Retroperitoneal disease does worse than extremity disease
- Spread: Haematogenous (lung dominant; liver for retroperitoneal/vascular); nodes rare
- Late recurrence: Recognised beyond 5 years, especially retroperitoneal
Side-by-Side Guidance from Major Societies
| Body | Diagnosis | Local Treatment | Systemic Therapy |
|---|---|---|---|
| ESMO/EURACAN (Europe) | Refer to sarcoma centre before biopsy; core biopsy with immunohistochemistry | Wide excision plus radiotherapy for deep/larger extremity tumours | Anthracycline-based for advanced disease; adjuvant individualised, not routine |
| NCCN (US) | Image-guided core biopsy at a sarcoma centre; multidisciplinary review | Limb-sparing wide excision with radiotherapy; re-excision for positive margins | Doxorubicin first line; trabectedin and eribulin in later lines |
| NICE / BSG sarcoma (UK) | Mandatory specialist sarcoma MDT before definitive treatment | Centralised surgery and radiotherapy at designated centres | Chemotherapy reserved for selected high-risk or advanced cases |
| TARPSWG (retroperitoneal consensus) | Multidisciplinary diagnosis; exclude dedifferentiated liposarcoma | En bloc resection of involved organs at high-volume centres | Radiotherapy and chemotherapy individualised |
Universal Principle Across Guidelines
Every major society agrees on three points regardless of region: any suspicious deep or enlarging soft tissue mass should be referred to a specialist sarcoma centre before biopsy, diagnosis should be made by planned core biopsy with immunohistochemistry, and definitive management should be set by a multidisciplinary sarcoma team. The main areas of disagreement are the thresholds for radiotherapy and for any systemic therapy.
High- vs Limited-Resource Practice Variation
High-Resource Settings
- Routine immunohistochemistry (desmin, SMA, h-caldesmon) and exclusion of GIST/dedifferentiated liposarcoma
- Centralised sarcoma MDTs, limb salvage with reconstruction, and specialist radiotherapy
- Access to MRI staging, PET-CT and histology-specific agents (trabectedin, eribulin)
- Pulmonary metastasectomy programmes for selected oligometastatic disease
Limited-Resource Settings
- Diagnosis may rest on morphology and a limited immunohistochemistry panel
- Later presentation with larger tumours; higher amputation rates
- Restricted radiotherapy and systemic-therapy access
- Telepathology and regional referral networks help bridge expertise gaps
Documentation and Safe-Practice Points
Applicable in any health system:
- Document the investigation pathway for any persistent or deep soft tissue mass (mitigates delayed diagnosis)
- Confirm pre-biopsy staging and that the biopsy was planned with the definitive surgeon
- Record exclusion of GIST and, in the retroperitoneum, of dedifferentiated liposarcoma
- Evidence of sarcoma MDT discussion before definitive treatment
- Informed consent covering recurrence and metastatic risk, possible organ or limb sacrifice
- A written long-term surveillance plan, given recognised late recurrence
LEIOMYOSARCOMA OF SOFT TISSUE
Clinical summary
Key Epidemiology
- •Malignant smooth-muscle sarcoma; roughly 10-20% of adult soft tissue sarcomas
- •Typical age 50-70 years, slight overall female predominance
- •Three groups: extremity/trunk, retroperitoneal/abdominal, and vascular (e.g. IVC)
- •Distinct from GIST - true leiomyosarcoma is KIT-negative
Diagnosis (Morphology plus IHC)
- •Intersecting fascicles of spindle cells with blunt-ended (cigar-shaped) nuclei
- •Brightly eosinophilic, fibrillary cytoplasm
- •Positive: desmin, smooth muscle actin (SMA), h-caldesmon
- •Negative KIT/DOG1 excludes GIST; check MDM2/CDK4 in retroperitoneum to exclude dedifferentiated liposarcoma
Grading and Staging
- •FNCLCC grade = differentiation + mitotic count + necrosis, mapped to grade 1-3
- •Grade is the most important histopathological prognostic factor
- •AJCC staging by grade, size and metastasis (separate scheme for retroperitoneum)
- •Most clinically significant tumours are intermediate to high grade
Investigation and Biopsy
- •MRI is the gold standard for local staging of the mass
- •CT chest for lung metastases; CT abdomen/pelvis (and liver) for retroperitoneal/vascular tumours
- •Image-guided core biopsy with tract planned by the definitive surgeon
- •Never shell out an undiagnosed deep mass - refer to a sarcoma centre first
Treatment
- •Wide local excision with negative margins is the curative backbone
- •Radiotherapy improves local control for deep or larger extremity tumours
- •Adjuvant chemotherapy is NOT routine - EORTC 62931 showed no survival benefit
- •Advanced disease: doxorubicin first line, then trabectedin and eribulin
- •Metastasectomy for selected resectable oligometastatic lung disease
Adverse Prognostic Factors (GRIMS)
- •Grade high (FNCLCC 3)
- •Retroperitoneal / deep site
- •Incomplete (positive) margins
- •Measurement large (size over 5cm)
- •Spread (metastatic at presentation)
Prognosis and Surveillance
- •Grade and size are the dominant independent predictors of survival
- •Margin status drives local recurrence
- •Spread is haematogenous (lung; liver for retroperitoneal/vascular); nodes rare
- •Late recurrence beyond 5 years is recognised - long-term surveillance is mandatory