Both procedures take out skin cancer. Where they part ways is in how the edges get checked. In Mohs surgery, the cancer comes out in thin layers, and nearly all of the edge is looked at under the microscope while you’re still there, so less healthy skin is lost. In a wide local excision, the cancer comes out in one piece with a planned border of normal skin around it, and a lab checks that tissue over the following days.
If you’ve just been told you have a basal cell carcinoma (BCC) or squamous cell carcinoma (SCC), perhaps on your face, you may have heard both terms and wondered which one you need. This guide explains how each method works, where each one fits, and what happens to the wound afterwards.
One point upfront, because it matters: Mohs surgery is performed by dermatologists with additional, specific Mohs training. Dr Justin Perron is a specialist plastic surgeon. He performs wide local excision and the reconstruction that follows, not Mohs surgery.
What is a surgical margin, and why does it matter?
A surgical margin is the border of normal-looking skin removed around a skin cancer. Cancer cells can spread a little further than you can see on the surface, so taking a margin gives the surgeon a buffer.
After surgery, a pathologist looks at the edges of the removed tissue under a microscope. “Clear margins” means no cancer cells were found at those edges. “Involved” or “close” margins mean cancer cells reached the edge, or came very near it, and more treatment may be needed.
What is wide local excision?
Wide local excision (also called standard or conventional excision) removes the cancer in one piece, together with a margin of skin that is planned before surgery. The wound is usually closed straight away, and the tissue is sent to a pathology laboratory.
In the lab, the specimen is sliced into cross-sections, and a pathologist checks the margins on those slices. This samples the edge rather than examining all of it. Cleveland Clinic estimates that, in general, less than 1% of the margin is checked this way. Results usually come back within several days, and your doctor will go through them with you.
For most skin cancers this works well. It’s the most common way skin cancers are removed in Australia, and it can be done in rooms, a day hospital or a hospital, depending on the size and site of the cancer.
What is Mohs micrographic surgery?
Mohs micrographic surgery removes the cancer in stages. The surgeon takes the visible cancer with a narrow margin, then maps and colour-codes the tissue so every part of it can be matched to its exact spot on your skin.
The tissue is frozen and processed on site while you wait. The Mohs surgeon then examines the deep and side margins under the microscope. If cancer cells remain anywhere, a further thin layer is taken from just that area. This repeats until the margins are clear, and only then is the wound closed.
Because close to 100% of the margin is examined, Mohs can remove the cancer while keeping as much healthy skin as possible. The trade-off is time. A Mohs procedure can take a few hours or most of a day, since each stage involves waiting for the slides to be prepared.
What are the main differences between the two?
Both approaches aim to remove the whole cancer. Where they differ is in how much tissue they take, how the edges are checked, and who performs them. The table below sets out the key points side by side.
| Mohs surgery | Wide local excision | |
|---|---|---|
| How tissue is removed | In thin layers, in stages, on the same day | In one piece, with a margin planned before surgery |
| Initial margin | Narrow, with more taken only where cancer remains | Set in advance; often about 2 to 3mm for low-risk BCC and around 4mm for low-risk SCC, wider for high-risk tumours |
| How margins are checked | Close to 100% of the deep and side margins examined during surgery | Cross-sections of the margin checked in a laboratory afterwards |
| When results are known | On the day, before the wound is closed | Usually within several days, after the wound is closed |
| Who performs it | Dermatologists with additional accredited Mohs training | Specialist plastic surgeons, dermatologists, general surgeons and GPs |
| Commonly used for | High-risk, recurrent or poorly defined BCC and SCC, especially on the face | Many BCCs and SCCs, and the standard surgery for invasive melanoma |
How much tissue is removed?
Mohs begins with a narrow margin and only takes more where the microscope shows cancer is still present. Wide local excision uses a margin decided beforehand. For basal cell carcinoma, Cancer Council Australia’s clinical guidelines suggest 2 to 3mm for low-risk tumours and more than 5mm for high-risk ones. SCC margins tend to be a little wider, often around 4mm for low-risk and 6mm for high-risk tumours.
How are the margins checked?
With Mohs, almost the whole margin is examined during surgery, so any remaining cancer is found before the wound is closed. With standard excision, the pathologist checks samples of the margin in the days after surgery. If a margin turns out to be involved, you may need further surgery or another treatment.
Who performs each procedure?
In Australia, Mohs is performed by dermatologists who have completed further Mohs training accredited by the Australasian College of Dermatologists. Wide local excision is performed by a range of doctors, including specialist plastic surgeons. Plastic surgeons also commonly take care of the reconstruction, and some patients are referred to one after Mohs when the wound is large or complex.
When is Mohs preferred, and when is wide excision used?
Mohs tends to be chosen when the risk of leaving cancer behind is higher, or when every millimetre of skin counts. According to DermNet, that includes:
- recurrent or incompletely removed BCC or SCC
- large tumours, especially on the head and neck
- tumours with poorly defined borders
- BCCs with an aggressive growth pattern on the biopsy
- higher-risk SCCs, such as those on the ear or lip
- cancers in cosmetically sensitive areas such as the nose, eyelids and lips
Wide local excision is common, effective and appropriate for many other skin cancers, particularly well-defined tumours on the body, arms and legs. For a straightforward BCC on the back, for example, Mohs usually offers little extra benefit. Research suggests Mohs may have lower recurrence rates for high-risk BCC and SCC, although the difference matters less for low-risk cancers.
Is Mohs used for melanoma?
For most invasive melanomas, no. Australian clinical guidelines recommend wide local excision, with the margin based on how thick the melanoma is (its Breslow thickness) on the biopsy. The recommended margins are:
- melanoma in situ (confined to the top layer of skin): 5 to 10mm
- melanoma 1mm thick or less: 1cm
- melanoma more than 1mm and up to 4mm thick: 1 to 2cm
- melanoma more than 4mm thick: 2cm
One reason Mohs isn’t routine for melanoma is that melanoma cells can be hard to identify on the frozen sections standard Mohs relies on. For some melanoma in situ, especially lentigo maligna on the face, specialists may use Mohs or a staged excision with permanent (paraffin) sections. These techniques check the margins carefully before the wound is closed. Your specialist will explain whether this approach applies to you.
What happens to the wound after removal?
Once the cancer is out, the wound needs to heal. The main options are:
- Direct closure: the edges are stitched together in a straight line. This suits smaller wounds where the skin can stretch.
- Local flap: nearby skin, with its own blood supply, is moved across to cover the wound. Flaps are often used on the face, where matching colour and texture matters.
- Skin graft: a thin piece of skin is taken from another part of the body to cover the wound.
- Healing on its own: some small wounds in certain sites are left to heal naturally.
The choice depends on the size and depth of the wound, where it is, the quality of the surrounding skin and your general health. For melanoma and some higher-risk cancers, the surgeon may wait for clear margins before a flap is used. You can read more about reconstruction after skin cancer removal and skin cancer surgery in Brisbane.
Like any surgery, skin cancer removal and reconstruction carry risks. These include:
- scarring, which can be red, raised or wider than expected
- infection
- bleeding, bruising or swelling
- wound breakdown, or partial loss of a flap or graft
- changes in sensation or nerve function near the wound
- a wound that is larger than expected once margins are cleared
- cancer that has not been fully removed, or that comes back later
- the need for further surgery
Surgery can remove the cancer and give the pathologist tissue to confirm what it was and whether the margins are clear. Results vary between patients, so it’s worth talking through the benefits and risks for your own situation before deciding.
How do I decide which is right for me?
You don’t need to work this out alone. The decision usually depends on the type of cancer, what the biopsy shows, where it sits, whether it has been treated before and your general health.
Your GP or skin cancer doctor is a good starting point. They can refer you to a dermatologist for Mohs, or to a specialist plastic surgeon for excision and reconstruction. Complex cases are sometimes discussed by a multidisciplinary team that may include dermatologists, surgeons, pathologists and radiation oncologists. If you live in Brisbane or South East Queensland, a consultation is a chance to look at the lesion, its site and the pathology together, and to ask about the options that suit you.
Frequently asked questions
Is Mohs surgery better than standard excision?
Neither is better for everyone. Mohs checks almost the whole margin during surgery and spares healthy skin, which suits high-risk, recurrent or facial basal and squamous cell carcinomas. Wide local excision is effective for many other skin cancers and is the standard surgery for invasive melanoma. The right choice depends on the cancer and its site.
Is Mohs surgery available in Australia?
Yes. In Australia, Mohs surgery is performed by dermatologists who have completed additional Mohs training accredited by the Australasian College of Dermatologists. It is offered by a relatively small number of specialists. Not every skin cancer needs Mohs, and your treating doctor can advise whether it suits your lesion and its location.
What margin is taken for a basal cell carcinoma?
With standard excision, Australian guidelines suggest a margin of about 2 to 3mm of normal-looking skin for low-risk tumours, and more than 5mm for high-risk tumours. The exact margin depends on the type, size and site of the cancer. Mohs starts with a narrower margin because the edges are checked during surgery.
Does wide local excision leave a bigger scar than Mohs?
Often, yes, because standard excision removes a set border of healthy skin rather than only what is needed. Scar size also depends on the size and site of the cancer and how the wound is closed. Every method of skin cancer removal leaves a scar, and how it heals varies between people.
Why is Mohs not usually used for melanoma?
Australian guidelines recommend wide local excision for invasive melanoma, with margins based on the thickness of the tumour. Melanoma cells can also be hard to see on the frozen sections used in standard Mohs. Mohs-style or staged excision is sometimes considered for melanoma in situ, such as lentigo maligna, on the face.
Do I stay awake for the procedure?
In most cases, yes. Standard excisions and Mohs are both usually done with a local anaesthetic. You’ll be awake, but the area is numbed. If the cancer is large, sits somewhere tricky or needs a more involved repair, sedation or a general anaesthetic might be used instead. Your surgeon will talk you through the options and their risks.
Why choose Dr Justin Perron for skin cancer surgery in Brisbane
Dr Justin Perron (MBBS, FRACS Plastics) is a Specialist Plastic and Reconstructive Surgeon. He completed his Australian Fellowship in Plastic and Reconstructive Surgery with the Royal Australasian College of Surgeons (RACS). His training took him from South East Queensland to Perth in Western Australia, and he has worked throughout Queensland, from Townsville to Brisbane, Redcliffe, Caboolture and the Gold Coast.
In skin cancer care, Dr Perron performs wide local excision and reconstruction, including direct closure, local flaps and skin grafts. He plans the excision and the repair together, with the aim of balancing cancer removal with function and appearance. He does not perform Mohs surgery.
Dr Perron presents at surgical conferences, has published articles in a number of journals and keeps up to date with developments across plastic and reconstructive surgery.
He operates at The Wesley Hospital, St Andrew’s War Memorial Hospital, Brisbane Private Hospital and Spring Hill Specialist Day Hospital. His private rooms are at Herstellen Clinic, 490 Boundary Street, Spring Hill, Brisbane QLD 4000. AHPRA registration: MED0000959827.
A referral from your GP or treating specialist is required for a consultation. You can read more about Dr Perron’s background and professional memberships here:
- About Dr Perron
- Australasian Society of Aesthetic Plastic Surgeons (ASAPS) profile
- ANZ Board of Cosmetic Plastic Surgery profile
- Plastic Surgery Hub profile
Disclaimer: The information here is general in nature and can’t replace advice about your own situation. Any surgery, skin cancer surgery included, has risks, and outcomes differ from one person to the next. Talk to your GP and a qualified specialist before you decide on treatment.
Further reading
- Reconstruction after skin cancer and melanoma removal
- Melanoma skin cancer surgery: the basics
- Scar revision in Brisbane
- Skin lesion removal in Brisbane
Medical references
- Cleveland Clinic. Mohs surgery. https://my.clevelandclinic.org/health/treatments/13312-mohs-surgery
- DermNet. Mohs micrographic surgery. https://dermnetnz.org/topics/mohs-micrographic-surgery
- DermNet. Skin flaps. https://dermnetnz.org/topics/skin-flaps
- DermNet. Skin grafting. https://dermnetnz.org/topics/skin-grafting
- DermNet. Wound closure. https://dermnetnz.org/topics/wound-closure
- Australian Journal of General Practice (RACGP). Marking a surgical margin for excision of a keratinocyte cancer, 2021. https://www1.racgp.org.au/ajgp/2021/june/marking-a-surgical-margin-for-excision-of-a-kerati
- Medical Journal of Australia. Updated evidence-based clinical practice guidelines for the diagnosis and management of melanoma: definitive excision margins for primary cutaneous melanoma, 2018. https://www.mja.com.au/journal/2018/208/3/updated-evidence-based-clinical-practice-guidelines-diagnosis-and-management
- healthdirect Australia. Basal cell carcinoma (BCC). https://www.healthdirect.gov.au/basal-cell-carcinoma
- healthdirect Australia. Squamous cell carcinoma (SCC). https://www.healthdirect.gov.au/squamous-cell-carcinoma
- healthdirect Australia. Skin cancer and melanoma. https://www.healthdirect.gov.au/skin-cancer-and-melanomas
