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Health condition · Clinically reviewed

Epithelioid sarcoma, INI1-negative pathology, specialist surgery and tazemetostat.

A rare soft-tissue sarcoma that hides as a benign lump. The right pathology and a supra-regional sarcoma centre change the outcome.

Jump to treatment
A radiographer guides a patient onto the bed of an advanced 3 Tesla MRI scanner in a London imaging suite

Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Checked against NCCN, ESMO and BSSMSD sarcoma standards you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK sarcoma pathways including tazemetostat and specialist commissioned services.

Key facts

Epithelioid sarcoma at a glance.

The essentials, in plain English. What it is, how it splits into two very different subtypes, and how it is treated in the UK today.

  • What it is

    A rare soft-tissue sarcoma defined by loss of the SMARCB1 (INI1) tumour-suppressor gene on immunohistochemistry.

  • Two subtypes

    Classic distal type in young adults on hands, forearms, feet or lower leg; proximal large-cell type in older adults, often axial and more aggressive.

  • How it presents

    A slow-growing, firm, often painless nodule or ulcer that is frequently misdiagnosed as a benign cyst or granuloma for months or years.

  • Node spread

    Regional lymph node metastasis is unusually common for a soft-tissue sarcoma, seen in roughly 40 per cent of cases.

  • Mainstay treatment

    Wide local excision at a specialist sarcoma centre, often with regional lymphadenectomy and adjuvant radiotherapy.

  • Targeted therapy

    Tazemetostat, an EZH2 inhibitor, is approved for advanced INI1-negative disease and delivered through specialist commissioned services.

Why this guide matters

Rare cancer, specialist pathway.

Outcomes in epithelioid sarcoma depend on getting to a specialist sarcoma centre before the first operation, not after. The three points below shape everything else on this page.

  • INI1 loss is the diagnosis

    A specialist sarcoma pathology review with INI1 immunohistochemistry and SMARCB1 molecular testing is what separates epithelioid sarcoma from its many mimics.

  • Sarcoma surgery is different

    Wide local excision with adequate margins at a supra-regional centre, often with regional lymphadenectomy, gives the best chance of long-term control.

  • Targeted therapy has arrived

    Tazemetostat, an EZH2 inhibitor, offers a targeted option for advanced INI1-negative disease and is delivered through specialist commissioned services.

How the diagnosis is made

From a stubborn lump to a specialist plan.

The steps a UK sarcoma team will normally follow, in order, so you know what to expect and why each one matters.

  1. 01

    Assessing

    Clinical examination

    A careful look at the lesion, regional lymph nodes and any ulcerated or non-healing area, with a low threshold for imaging.

  2. 02

    Assessing

    MRI of the affected area

    MRI defines the depth, size and relationship to nerves, vessels and bone before any biopsy is planned.

  3. 03

    Assessing

    Specialist sarcoma biopsy

    A core biopsy planned and reported at a specialist sarcoma centre, so the tract can be excised at definitive surgery.

  4. 04

    Confirming

    Histology and immunohistochemistry

    Epithelioid and spindle cells with geographic necrosis, loss of nuclear INI1 staining and positivity for cytokeratins, EMA and often CD34.

  5. 05

    Confirming

    Molecular confirmation

    SMARCB1 deletion or mutation identified on molecular testing, distinguishing epithelioid sarcoma from other INI1-deficient tumours.

  6. 06

    Confirming

    Staging imaging

    CT of the chest, abdomen and pelvis, with PET-CT where useful, to assess lymph nodes, lungs, bone, skin and liver.

  7. 07

    Preparing

    Sarcoma MDT and plan

    Review at a supra-regional UK sarcoma MDT to agree surgery, radiotherapy and systemic therapy through specialist commissioned services.

Typical timeline: first specialist review to full MDT plan in a few weeks.

Symptoms

What epithelioid sarcoma actually looks like.

The classic mix of a slow-growing nodule, a non-healing ulcer and a suspiciously enlarged node. And the features that mean it is time to refer.

  • Slow-growing firm nodule

    A painless, firm lump in the skin or deeper soft tissue that has often been present for months before referral.

  • Non-healing ulcer

    An ulcer or persistent wound that does not settle with dressings and is easily mistaken for a benign lesion.

  • Multiple nodules

    A chain of nodules along a limb, sometimes tracking towards the nearest lymph node basin.

  • Distal-limb pattern

    Hands, forearms, feet and lower legs are the classic sites in the young-adult distal type.

  • Proximal or axial mass

    Pelvis, perineum, groin or mediastinum in the older-adult proximal large-cell type, often deeper and more aggressive.

  • Regional lymph node lump

    An enlarged draining lymph node is common and can be the first sign of spread.

  • Diagnostic delay

    Frequently mislabelled as an inclusion cyst, granuloma annulare or dermatofibrosarcoma for a considerable period.

  • Red flag - any deep or growing lump

    Any deep, enlarging or recurrent soft-tissue lump needs specialist sarcoma referral, not repeated local excision.

Treatment

How epithelioid sarcoma is treated in the UK.

Specialist sarcoma surgery is the mainstay, with radiotherapy for higher-risk margins and tazemetostat or systemic therapy for advanced disease.

  • Wide local excision

    The mainstay of treatment. Specialist sarcoma surgery with adequate margins, tailored to the anatomy and often with reconstruction.

  • Regional lymphadenectomy

    Considered in the classic distal type given the high rate of nodal spread. Unusual for other soft-tissue sarcomas but well supported here.

  • Amputation where needed

    Reserved for extensive local disease of a distal extremity when limb-sparing surgery cannot achieve clear margins or preserve function.

  • Adjuvant radiotherapy

    For close or positive margins, large tumours or high-risk features. Delivered by specialist clinical oncology teams.

  • Tazemetostat (Tazverik)

    An EZH2 inhibitor for advanced or metastatic INI1-negative epithelioid sarcoma. Restores SMARCB1-mediated tumour suppression.

  • Cytotoxic chemotherapy

    Traditional sarcoma regimens such as doxorubicin, ifosfamide or gemcitabine and docetaxel. Responses are limited and use is reserved for advanced disease.

  • Checkpoint inhibitors

    Pembrolizumab and nivolumab produce occasional responses in trials. Access is through specialist centres and clinical studies.

  • Supportive and rehabilitation

    Specialist pain control, prosthetics, physiotherapy, psychological support and palliative care alongside disease-directed treatment.

What this guide is based on

The sources behind every claim on this page.

UK and international sarcoma guidance and specialist commissioning standards, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your sarcoma team knows the details of your imaging, histology and general health and can tell you which parts apply to you.

  • NCCN Clinical Practice Guidelines. Soft Tissue Sarcoma.

  • ESMO Clinical Practice Guidelines. Soft tissue and visceral sarcomas.

  • British Sarcoma Group and BSSMSD standards for sarcoma care in the UK.

  • NHS England service specification for specialist sarcoma services.

  • MHRA and NICE evaluations of tazemetostat for advanced epithelioid sarcoma.

  • Sarcoma UK. Patient information on epithelioid sarcoma.

Red flags

When a lump needs urgent sarcoma review.

Most soft-tissue lumps are benign. These are the features that mean the lump belongs in a specialist sarcoma clinic, not a local operating theatre.

  • Any deep soft-tissue lump

    A lump larger than 5 cm, deep to fascia, growing or painful deserves urgent sarcoma referral before local excision.

  • Non-healing wound or ulcer

    A persistent ulcer on a hand, foot or limb that has been treated as a cyst or granuloma is a classic epithelioid sarcoma trap.

  • Enlarged regional lymph node

    A firm, growing node draining a suspicious skin or soft-tissue lesion should be imaged and biopsied at a sarcoma centre.

  • Local recurrence after excision

    A lump that regrows after a benign-labelled excision needs the original pathology reviewed and re-imaging.

  • Unplanned or piecemeal excision

    A whoops procedure without prior imaging or specialist review compromises margins and outcomes and needs urgent sarcoma MDT input.

  • Pulmonary symptoms

    New breathlessness, cough or chest pain in a patient with known epithelioid sarcoma needs prompt CT to assess for lung metastases.

  • Neurovascular involvement

    Numbness, weakness or vascular compromise near a soft-tissue mass suggests deep invasion and warrants urgent MRI.

  • Family history of rhabdoid tumours

    A personal or family history of rhabdoid tumour, ATRT or other SMARCB1-related disease deserves specialist genetics review.

  • Rapid clinical change

    Sudden size increase, bleeding or systemic symptoms in a known lesion should trigger same-week imaging and MDT discussion.

Living with it

A rare cancer, with a specialist pathway.

Four things that make the biggest difference between diagnosis and long-term follow-up: staying in the sarcoma network, honouring the imaging schedule, working with rehabilitation and using the support that exists.

A quiet reminder

Rare cancers do better in specialist hands.

Ask to be seen at a supra-regional sarcoma centre from the first suspicious biopsy. The pathway is designed for exactly this.

  1. 01 Specialist care

    Stay within the sarcoma network

    UK sarcoma outcomes are best when surgery, radiotherapy and systemic therapy are delivered through a supra-regional specialist centre.

  2. 02 Surveillance

    Follow the imaging schedule

    Long-term follow-up with MRI of the primary site and CT of the chest is standard because late local and distant recurrence can occur.

  3. 03 Function

    Rehabilitation matters

    Physiotherapy, occupational therapy and prosthetic services help you regain function after limb or reconstructive surgery.

  4. 04 Support

    Use Sarcoma UK and peer networks

    Rare-cancer charities and specialist nurses can help with practical, emotional and financial questions between clinic visits.

Frequently asked

Everything we get asked about epithelioid sarcoma.

Quick answers on the two subtypes, INI1 loss, surgery, tazemetostat and inheritance.

  • What is epithelioid sarcoma?

    Epithelioid sarcoma is a rare soft-tissue sarcoma defined at the molecular level by loss of the SMARCB1 (INI1) tumour-suppressor gene. It has two main forms. The classic distal type appears in young adults on the hands, forearms, feet and lower legs. The proximal large-cell type affects older adults in the pelvis, perineum, groin or mediastinum and tends to behave more aggressively.

  • Why is it often diagnosed late?

    The classic form starts as a slow-growing, painless nodule or a stubborn ulcer, and is easily mistaken for an inclusion cyst, granuloma annulare or dermatofibrosarcoma. Many patients are treated locally for months or years before a specialist sarcoma biopsy shows loss of INI1 staining and confirms the diagnosis.

  • What does INI1 loss actually mean?

    INI1 is a protein made by the SMARCB1 gene and normally keeps cell growth in check. In epithelioid sarcoma the gene is deleted or mutated so the protein is absent, which is visible as loss of nuclear staining on immunohistochemistry. The same molecular loss is seen in other rare SMARCB1-deficient tumours such as rhabdoid tumours, ATRT and poorly differentiated chordoma.

  • What is the main treatment?

    Wide local excision at a specialist sarcoma centre is the mainstay. Because regional lymph node spread is unusually common for a soft-tissue sarcoma, regional lymphadenectomy is often considered in the classic distal type. Adjuvant radiotherapy is used for close or positive margins and high-risk features. Systemic therapy is added for advanced or metastatic disease.

  • Where does tazemetostat fit?

    Tazemetostat is an oral EZH2 inhibitor licensed for advanced or metastatic INI1-negative epithelioid sarcoma. It works by rebalancing the chromatin machinery that SMARCB1 loss disturbs, restoring tumour-suppressor signalling. In the UK it is delivered through specialist commissioned services and considered in patients who are not candidates for curative surgery.

  • Is epithelioid sarcoma inherited?

    Most cases are sporadic. A small minority sit within SMARCB1-related tumour syndromes, particularly when there is a personal or family history of rhabdoid tumours or ATRT. Specialist genetics review is offered when the clinical picture suggests a familial pattern.

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