A Lump Under the Skin? When to Get It Checked and Why the First Scan Matters

Written by the LSRI clinical team and medically reviewed by Dr Prashant Sankaye, Consultant MSK Radiologist, on 10 October 2026.

Finding a lump under the skin is very common, and most lumps are harmless: a lipoma (a soft lump of fat), a skin cyst or a swollen gland¹. Only a small number are a rare cancer called soft-tissue sarcoma, which can start in fat, muscle, blood vessels, ligaments or tendons². These cancers are usually painless at first and can feel like an ordinary lump, so many are found late, when already large^2,3.

This article explains which lumps need prompt checking, why a serious lump can be found late and why the first scan matters. We recommend having any lump scanned before it is removed or treated, usually with ultrasound first and MRI if needed. For a shorter overview, read our guide to the signs that a lump needs checking.

Is a lump under the skin usually harmless?

Yes. Most lumps are harmless, but a lump that is still there after two weeks, or that worries you, should be checked by a GP¹.

Common harmless lumps include:

• Lipoma: a soft lump of fat that moves under the skin¹.
• Skin cyst: a smooth lump under the skin¹.
• Swollen glands (lymph nodes): often in the neck, armpit or groin¹.

In an average general practice of 3,000 patients, at least three harmless soft-tissue tumours a year can be expected, but only about one sarcoma every 24 years⁴.

In the UK, sarcomas make up only about 1.4% of all cancers, around 5,300 new diagnoses a year³.

Which lumps need prompt assessment?

A lump should be checked promptly if it is growing, larger than about 5 cm (roughly a golf ball), deep, painful, or back after removal^5,7,13.

The more of these features a lump has, the higher the risk⁵. But they are not perfect. UK guidelines note that, on their own, these features did not reliably separate cancerous lumps from much more common harmless ones, and only a small percentage of people referred because of them prove to have a sarcoma³. So the right response to a warning feature is a scan, not panic, and not an operation.

Why are some serious lumps found late?

Because an early sarcoma usually feels like an ordinary lump, and the route to a specialist has several steps.

• It is usually painless at first. A typical sarcoma is a solid, painless lump that is hard to move, keeps growing and may only become painful as it gets bigger².
• It is rare. A GP practice sees far more harmless lumps than cancerous ones⁴.
• Deep lumps are harder to recognise, for example in the thigh³.
• An injury can seem to explain a lump. A sarcoma and a haematoma (a collection of blood, often after an injury) can look alike, even on ultrasound¹⁴. The story of the injury, such as how hard it was and whether there was bruising, needs to fit the scan¹⁴.
• The route has many steps. In a review of 76 studies, the time from first symptom to diagnosis of soft-tissue sarcoma varied from about 4 weeks to over 11 years between studies¹⁵.

Many sarcomas are large when found: UK guidelines report a typical (median) size at diagnosis of over 9 cm³.

What can delay, or the wrong first operation, cost?

Larger tumours at diagnosis do worse⁸, and an unplanned first removal is linked to more local recurrence and more surgery^3,9,10. Evidence that a longer wait on its own worsens survival is mixed^8,15.

Size at diagnosis

In a UK series of 1,460 people with a newly diagnosed bone or soft-tissue sarcoma, outcomes worsened as tumour size at diagnosis increased, even when the cancer had not spread⁸. For soft-tissue sarcoma that had not spread, compared with tumours of 5 cm or less, the relative risk of death over follow-up (hazard ratio) was about 2.9 times higher at 5 to 10 cm and about 8.5 times higher above 25 cm⁸.

The link between time and outcome is less simple. In the UK series, symptom duration did not correlate with tumour size, and people whose symptoms had lasted over a year had a slightly better outlook⁸. The review of 76 studies found no clinically meaningful cut-off between a short and a long delay, and conflicting results for survival in soft-tissue sarcoma, possibly because studies could not allow for how aggressive each tumour was¹⁵. This does not mean that waiting is safe. The aim is not to rush every lump, but to recognise a growing or suspicious lump and investigate it properly the first time.

The “whoops” operation

An unplanned excision, sometimes called a “whoops” procedure, is when a lump is cut out as if harmless and the laboratory then finds a sarcoma. It is reported to account for up to 40% of first operations for soft-tissue sarcoma⁹. Most involve lumps in or just under the skin³.

Sarcoma surgery should be planned from MRI and a biopsy taken beforehand⁵. After an unplanned excision, further surgery to the area where the lump was removed (re-excision) is often advised, though it is not suitable for every tumour^3,10,12:

• In a combined analysis of 43 studies, tumour was still present at re-excision in 59% of patients where this was checked, and unplanned excision was linked to a 35% higher risk of local recurrence (the cancer coming back in the same place) at five years¹⁰.
• UK guidelines add that it can mean more complex surgery and more need for radiotherapy, though studies of its effect on local control conflict³.

In the combined analysis, five-year survival was not significantly worse after unplanned excision, and amputation and reconstruction rates were not higher¹⁰. But local recurrence was itself linked to worse survival¹⁰. The better path is to avoid the problem: scan first, then a biopsy by the specialist hospital team if needed, then operate once. For the wider picture, see why early imaging matters across muscle, bone and joint problems.

How should a lump be investigated?

Scan first, usually with ultrasound and then MRI if needed. If the scan is worrying, a specialist hospital team plans a biopsy and then any surgery^3,11,12.

Step 1: history and examination

Good practice is to record how long the lump has been there, whether it has changed in size, any symptoms and any injury, and to examine the lump, including at the time of an ultrasound scan¹⁶.

Step 2: ultrasound, usually the first scan

Ultrasound uses sound waves to make live pictures, with no radiation. UK guidelines call it an effective first test for sorting lumps³, and European guidelines recommend it first for a lump that is small (under 5 cm) and within reach of the probe¹¹. It can confirm typical lipomas and quickly flags lumps that need more tests^5,7. For a lump that is growing or larger than 5 cm, UK guidelines advise an urgent ultrasound scan or direct referral to a sarcoma diagnostic centre⁵.

Step 3: MRI for deep, large, growing or uncertain lumps

MRI uses a strong magnet and radio waves to show soft tissues in detail, without radiation. European guidelines call it the imaging technique of choice for lumps over 5 cm or uncertain on ultrasound, and suggest considering MRI first when cancer is suspected, a lump is deep or growing quickly, or bone or a joint is involved¹¹. MRI should be done before a biopsy, not after, when it will help to show what the lump is¹¹.

Step 4: a biopsy by the hospital specialist team, if needed

If imaging suggests a sarcoma, or cannot rule one out, referral to a specialist sarcoma centre should come before any biopsy¹¹. The hospital team then arranges the standard test, a core needle biopsy: a hollow needle, usually guided by imaging, takes several thin cores of tissue^3,12. They plan it so the needle track can be removed with the tumour at surgery³.

Step 5: treatment planned by the team

Surgery is the main treatment. Radiotherapy and drug treatments are used for some sarcomas, followed by regular check-ups³.

What should a scan report say?

A good report on a lump states whether it looks benign, indeterminate or suspicious for malignancy, and recommends the next step¹⁶. When features are worrying, guidelines advise urgent referral to a sarcoma service, and the report should make that recommendation clear^7,11,16.

What scans cannot do

• Ultrasound depends on the operator. Its accuracy relies heavily on the skill of the person scanning^3,16.
• Some lumps are indeterminate. A lump that does not look clearly harmless on ultrasound needs further imaging, usually MRI, before a firm answer^7,11.
• Scans do not prove the diagnosis. Imaging suggests what a lump is; a biopsy examined by a pathologist confirms it^3,12.

Does every lump need a scan?

In our view, yes: we recommend having any lump scanned and checked, usually with ultrasound first and MRI only if needed, and certainly before it is removed or treated. That does not mean every lump is a worry: most are harmless¹, and for a typical lump near the surface, such as a lipoma, ultrasound is often enough^5,7.

Who looks after a lump that could be serious?

A specialist sarcoma service: a hospital team that sees many of these rare cancers. Radiologists, surgeons, pathologists, oncologists and specialist nurses plan each person’s care together at a multidisciplinary team (MDT) meeting³.

UK guidelines recommend that anyone with a suspected soft-tissue sarcoma is referred to a specialist regional sarcoma service³, and European guidelines recommend early referral and treatment in specialist (reference) centres or networks¹².

In a French national study of 29,497 people with a new sarcoma, surgery in a reference centre was linked to less relapse and about a 32% lower risk of death¹⁷. This was an observational study, so some of the difference may reflect which patients were treated where.

What should you do if you have a lump?

1. Do not ignore a lump that is changing. See a GP if a lump lasts over two weeks, grows, is hard and does not move, is painful, red or hot, or comes back after removal¹.
2. Keep a simple record. Measure the lump and take a dated photo beside a ruler every few weeks. Growth is the most useful single warning sign⁵. You do not need to wait for several measurements before seeing a GP.
3. Tell your GP about any warning feature: growing, larger than about 5 cm (roughly a golf ball), deep or fixed, or painful^5,13.
4. Ask for a scan before any lump is removed or treated. We recommend this for every lump, usually with ultrasound first and MRI if needed. Guidelines advise that a lump with a warning feature is assessed urgently^5,7.
5. Bring previous scans and reports. Earlier images show whether a lump has grown.
6. If a scan is worrying, ask for referral to a specialist sarcoma centre before any biopsy. The biopsy should be planned and done by the hospital team that will treat you^3,11.
7. If a removed lump turns out to be a sarcoma, ask for prompt specialist referral. European guidelines advise that re-excision at a reference centre should be considered¹².

How LSRI can help

LSRI is a doctor-led musculoskeletal imaging clinic. Our lumps and bumps clinic offers ultrasound-led assessment of lumps, reported by a consultant MSK radiologist. We add MRI when a lump is deep, large or uncertain on ultrasound.

• MRI from £375 per body part, including the scan, a specialist report and access to your images (from £425 with a consultation).
• Reports within 24 hours.
• Clinics at Harley Street (W1G 9QJ) and Harrow (HA2 7SJ). Phone 0203 633 5040.
• Already had a scan elsewhere? We offer a second opinion on scans and reports.

If a scan shows features that need specialist assessment, the report says so clearly and advises urgent referral to a sarcoma service. LSRI does not carry out biopsies or provide cancer treatment. If a biopsy is needed, we recommend it is done in the NHS by the hospital’s specialist sarcoma team, who will also plan any treatment.

Reading this from outside the UK? The warning features and the scan-first, biopsy-at-a-specialist-centre pathway apply everywhere and match European guidance^11,12. Ask your doctor for referral to a recognised sarcoma reference centre or orthopaedic oncology service, ideally before any biopsy or surgery. European radiology guidelines also support remote second-opinion review of scans by a tumour centre when MRI findings are indeterminate or suspicious¹¹.

Frequently asked questions

How can I tell if a lump is a harmless lipoma?

You cannot reliably tell by feel alone, which is why we recommend a scan. Lipomas are by far the most common soft-tissue lump of the limbs and trunk seen in primary care³, and ultrasound can often confirm a typical lipoma⁵. If imaging is unsure, a biopsy by a specialist hospital team is the way to confirm the diagnosis^3,11.

Is a painless lump less worrying?

Not necessarily. Most early sarcomas are painless, and the most common presentation is a painless lump that is getting bigger^2,3. Pain is a warning feature when present⁶. But a lack of pain is not reassuring on its own if a lump is growing, large or deep.

What size of lump should be checked?

Any lump that lasts more than two weeks, or worries you, is worth showing a GP¹. A lump larger than about 5 cm, roughly a golf ball, should be assessed promptly, especially if growing or deep^5,13. Smaller lumps can still be sarcomas, so growth matters as well as size⁵.

Is ultrasound enough, or do I need an MRI?

Ultrasound is usually the first scan, and for a small lump near the surface it can often confirm a harmless lump^3,5,11. Deep, large, rapidly growing or uncertain lumps are usually assessed with MRI¹¹.

References

1. NHS. Lumps. Page last reviewed 5 February 2024. nhs.uk
2. NHS. Soft tissue sarcoma: What is soft tissue sarcoma? and Symptoms. Pages last reviewed 20 February 2024. nhs.uk and nhs.uk
3. Hayes AJ, Nixon IF, Strauss DC, Seddon BM, Desai A, Benson C, et al. UK guidelines for the management of soft tissue sarcomas. Br J Cancer 2025;132(1):11-31. doi:10.1038/s41416-024-02674-y
4. Mannan K, Briggs TW. Soft tissue tumours of the extremities (editorial). BMJ 2005;331(7517):590. doi:10.1136/bmj.331.7517.590
5. Dangoor A, Seddon B, Gerrand C, Grimer R, Whelan J, Judson I. UK guidelines for the management of soft tissue sarcomas. Clin Sarcoma Res 2016;6:20. doi:10.1186/s13569-016-0060-4
6. Johnson CJ, Pynsent PB, Grimer RJ. Clinical features of soft tissue sarcomas. Ann R Coll Surg Engl 2001;83(3):203-205. PMID: 11432141
7. British Sarcoma Group. Ultrasound screening of soft tissue masses in the trunk and extremity: a BSG guide for ultrasonographers and primary care. 2019. remedy.bnssg.icb.nhs.uk
8. Grimer RJ. Size matters for sarcomas! Ann R Coll Surg Engl 2006;88(6):519-524. doi:10.1308/003588406X130651
9. Qureshi YA, Huddy JR, Miller JD, Strauss DC, Thomas JM, Hayes AJ. Unplanned excision of soft tissue sarcoma results in increased rates of local recurrence despite full further oncological treatment. Ann Surg Oncol 2012;19(3):871-877. doi:10.1245/s10434-011-1876-z
10. Larios F, Gonzalez MR, Ruiz-Arellanos K, Aquilino E Silva G, Pretell-Mazzini J. Is unplanned excision of soft tissue sarcomas associated with worse oncological outcomes? A systematic review and meta-analysis. Cancers (Basel) 2024;16(2):443. doi:10.3390/cancers16020443
11. Noebauer-Huhmann IM, Vanhoenacker FM, Vilanova JC, Tagliafico AS, Weber MA, Lalam RK, et al. Soft tissue tumor imaging in adults: European Society of Musculoskeletal Radiology-Guidelines 2023: overview, and primary local imaging: how and where? Eur Radiol 2024;34(7):4427-4437. doi:10.1007/s00330-023-10425-5
12. Gronchi A, Miah AB, Dei Tos AP, Abecassis N, Bajpai J, Bauer S, et al. Soft tissue and visceral sarcomas: ESMO-EURACAN-GENTURIS Clinical Practice Guidelines for diagnosis, treatment and follow-up. Ann Oncol 2021;32(11):1348-1365. doi:10.1016/j.annonc.2021.07.006
13. Sarcoma UK. Do I have sarcoma? Last reviewed 2023. sarcoma.org.uk
14. Berry C, Charnock M. Sarcoma or haematoma? If only it was that simple! Part 1. Ultrasound 2025;33(1):58-65. doi:10.1177/1742271X241275136
15. Soomers V, Husson O, Young R, Desar I, van der Graaf W. The sarcoma diagnostic interval: a systematic review on length, contributing factors and patient outcomes. ESMO Open 2020;5(1):e000592. doi:10.1136/esmoopen-2019-000592
16. The Royal College of Radiologists. Audit of ultrasound technique for the evaluation of soft tissue lumps (AuditLive template). Published 26 January 2021. rcr.ac.uk
17. Blay JY, Honoré C, Stoeckle E, Meeus P, Jafari M, Gouin F, et al. Surgery in reference centers improves survival of sarcoma patients: a nationwide study. Ann Oncol 2019;30(7):1143-1153. doi:10.1093/annonc/mdz124

Book an appointment

Call 0203 633 5040 or book online. Clinics at Harley Street (W1G 9QJ) and Harrow (HA2 7SJ). If you have emergency symptoms, go to A&E or call 999 instead.