Soft tissue sarcoma of the trunk and abdominal wall
Soft tissue sarcomas are malignant tumours arising from connective tissue — muscle, fat, fibrous tissue, blood vessels and nerves. They are uncommon, accounting for around one per cent of adult cancers, and they comprise more than seventy distinct subtypes. Those arising in the trunk and abdominal wall present a particular problem: the space available allows them to grow substantially before causing symptoms, and they are frequently mistaken for a lipoma or a muscle strain. The single most consequential decision in a patient's care is often made before any diagnosis is confirmed — whether the lump is referred to a sarcoma centre or simply removed locally.
How they form
Sarcomas arise from mesenchymal stem cells that differentiate along various lineages — hence the diversity of subtypes. Genetically they fall into two broad groups, and the distinction is useful:
- Simple karyotype sarcomas — driven by a single defining genetic event, usually a chromosomal translocation creating a fusion gene that acts as an aberrant transcription factor. Examples include synovial sarcoma (SS18-SSX), myxoid liposarcoma (FUS-DDIT3) and Ewing sarcoma (EWSR1-FLI1). These fusion genes are diagnostically definitive and are increasingly therapeutic targets.
- Complex karyotype sarcomas — chaotic chromosomal rearrangement with loss of tumour suppressors such as TP53 and RB1. Undifferentiated pleomorphic sarcoma and leiomyosarcoma fall here. No single target exists.
Most arise sporadically. Recognised causes and associations:
- Previous radiotherapy — radiation-induced sarcoma typically appears in the field of treatment after a latency of five to fifteen years, and is a recognised late complication of treatment for breast, lymphoma and other cancers
- Chronic lymphoedema — Stewart-Treves syndrome, angiosarcoma arising in a chronically swollen limb
- Genetic syndromes — Li-Fraumeni syndrome (germline TP53), neurofibromatosis type 1 (malignant peripheral nerve sheath tumour), hereditary retinoblastoma, familial adenomatous polyposis (desmoid tumours)
- chemical exposures such as vinyl chloride (hepatic angiosarcoma)
The common subtypes in adults are undifferentiated pleomorphic sarcoma, liposarcoma, leiomyosarcoma, myxofibrosarcoma, synovial sarcoma and malignant peripheral nerve sheath tumour.
Myxofibrosarcoma deserves specific mention for trunk and abdominal wall disease, because it has an unusual and treacherous growth pattern: it extends in long, thin tails along fascial planes far beyond the apparent edge of the tumour, invisible on examination and often underestimated on imaging. It has one of the highest local recurrence rates of any sarcoma, and its resection must be wider than the visible lesion suggests.
Symptoms
Sarcomas are usually painless, which is precisely why they are neglected.
- A painless, enlarging lump — growth is the key feature. A lump that is growing is abnormal whatever its size.
- a lump deep to the deep fascia, fixed rather than mobile
- pain, if a nerve is compressed or the tumour is large
- skin changes over a superficial tumour
- a mass in the abdominal wall mistaken for a hernia
- systemic symptoms are usually absent
The referral criteria that matter. Any soft tissue lump with one or more of the following should be referred for urgent imaging before any attempt at removal:
- larger than 5cm (roughly the size of a golf ball)
- deep to the deep fascia
- increasing in size
- painful
- recurrent after previous excision
A lump meeting any of these is a sarcoma until proved otherwise. This rule exists because the commonest pathway to a poor outcome is an "obvious lipoma" removed in a minor operating theatre, which turns out to be a sarcoma with tumour left behind.
How the diagnosis is made
- MRI — the investigation of choice for trunk, abdominal wall and limb lesions. It defines the size, depth, relationship to fascia, muscle, vessels and nerves, and identifies the fascial tails of myxofibrosarcoma. It should be performed before biopsy, since biopsy alters the appearances.
- CT of the chest — for staging, as the lung is the commonest site of metastasis.
- Image-guided core biopsy — performed by or in consultation with the sarcoma centre that will operate, because the biopsy track must be positioned so that it can be excised with the specimen. A poorly placed biopsy track contaminates tissue planes and can convert a straightforward resection into a much larger one. Fine-needle aspiration is inadequate for primary diagnosis.
- Pathology review — including immunohistochemistry and molecular testing for fusion genes, by a pathologist experienced in sarcoma. Diagnostic revision on expert review is common.
- Grading by the FNCLCC system — differentiation, mitotic count and necrosis — which predicts metastatic risk more reliably than size.
Treatment
Surgery
Wide local excision with a cuff of normal tissue is the cornerstone. The objective is a margin of normal tissue on all sides, respecting anatomical barriers such as fascia, which resist tumour spread.
For the abdominal wall, this frequently means full-thickness resection of the affected wall, with reconstruction using mesh, and occasionally a muscle or fascial flap. Involvement of underlying structures may require en bloc resection of peritoneum, bowel or other organs.
The problem of unplanned excision. A significant proportion of patients reach a sarcoma centre only after the lump has already been removed elsewhere as a presumed lipoma or cyst. The tumour bed is then contaminated with microscopic disease, residual tumour is found in a large proportion of re-excision specimens, and the subsequent operation is bigger than the original one would have been. This is avoidable, and avoiding it is simply a matter of imaging a suspicious lump before removing it.
Radiotherapy
Used in combination with surgery for high-grade, large or deep tumours, and it substantially improves local control.
- Preoperative radiotherapy — lower total dose, smaller field, better long-term function, but a higher rate of wound healing complications.
- Postoperative radiotherapy — fewer wound problems, but a higher dose over a larger field and more late fibrosis.
The choice is individualised, and both are legitimate.
Systemic therapy
Chemotherapy sensitivity varies greatly by subtype, and this is where subtype-specific knowledge matters:
- Doxorubicin with ifosfamide is the standard for advanced disease
- Synovial sarcoma and myxoid liposarcoma are relatively chemosensitive
- Gemcitabine and docetaxel for leiomyosarcoma and undifferentiated pleomorphic sarcoma
- Taxanes for angiosarcoma
- Trabectedin, pazopanib, eribulin in later lines
- Adjuvant chemotherapy after complete resection is of debated benefit and is offered selectively to fit patients with large, high-grade tumours
- Newer approaches include engineered T-cell therapies targeting specific fusion-associated antigens in synovial sarcoma
Metastatic disease
Resection of limited lung metastases is worthwhile in selected patients and can achieve long survival. Stereotactic radiotherapy and ablation are alternatives.
Recovery
Recovery depends on the extent of resection and reconstruction. Abdominal wall resection with mesh reconstruction involves a hospital stay of around a week and a recovery of two to three months, with restrictions on lifting while the reconstruction heals. Wound complications are commoner where preoperative radiotherapy has been given, and are a recognised part of that trade-off.
Follow-up
Clinical examination and imaging of the primary site, with CT of the chest, at intervals determined by grade — three to six monthly for high-grade tumours initially, extending to annually, and continuing for at least ten years.
When to seek an opinion
Any soft tissue lump that is larger than 5cm, deep, growing, painful, or has recurred after previous removal should be imaged by MRI and referred to a sarcoma centre before any attempt at excision. This single step is the most effective thing that can be done to improve outcomes in this disease.
Common questions
I have a lump but it does not hurt. Is that reassuring?
No — most sarcomas are painless, which is exactly why they are often ignored for months. The important feature is not pain but growth. A lump that is getting bigger should be imaged, regardless of whether it hurts.
How can I tell the difference between this and a lipoma?
You cannot reliably, and neither can examination alone. Lipomas are far commoner, but features that should trigger a scan are size above about five centimetres, sitting deep rather than just under the skin, growing, being painful, or having come back after previous removal. An MRI answers the question, and it should be done before anything is removed.
My lump was removed and now I am told it was a sarcoma. What happens?
You will be referred to a sarcoma centre, imaged, and in most cases advised to have a further, wider operation on the area. This is because microscopic tumour is commonly left behind after an operation that was not planned as a cancer operation. It is a recognised situation and it is treatable — but it is the reason imaging before removal matters so much.
Why does the biopsy have to be done by the specialist centre?
Because the track the needle takes becomes contaminated with tumour cells and has to be removed with the tumour at the operation. If the track is placed in the wrong direction, the subsequent operation becomes considerably larger. A few days' wait to have it done in the right place is worth it.
Will I need radiotherapy as well as surgery?
For larger, deeper or higher-grade tumours, usually yes, as it substantially reduces the chance of the tumour returning in the same place. It can be given before or after the operation — before means a smaller dose and better long-term function but more wound healing problems; after means fewer wound problems but more long-term stiffness. Both are reasonable and the choice is discussed with you.
Do I need chemotherapy?
It depends heavily on the exact subtype, since some respond well and others hardly at all. For disease that has spread, chemotherapy is the main treatment. After complete removal of a localised tumour, its benefit is debated, and it is offered selectively to fit patients with large, high-grade tumours.
Will it come back?
That depends on the grade, the size, the subtype and whether the operation achieved clear margins. High-grade tumours carry a real risk of spread to the lungs, which is why chest scans are part of follow-up for at least ten years. Local recurrence is considerably less likely after a properly planned wide excision with radiotherapy than after an unplanned removal.
Is a lump at the site of my old radiotherapy significant?
It should be checked. Sarcomas can develop in a previously irradiated area, typically five to fifteen years afterwards. It is an uncommon late effect, but a new growing lump within an old radiotherapy field is a reason for prompt imaging rather than watchful waiting.
Related conditions
Other conditions of the sarcoma & retroperitoneal covered on this site:
- Retroperitoneal liposarcoma
- Leiomyosarcoma
- Desmoid tumour (aggressive fibromatosis)
- Benign retroperitoneal tumours and masses
This page provides general information and does not replace an individual medical consultation. A suspicious soft tissue lump should be imaged and referred to a specialist sarcoma centre before excision.