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Dermatological surgery and laser unit

Providing a specialist service to treat skin cancer


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Our service

Our dermatological surgery and laser unit (DSLU) is the largest and longest established centre in the UK with over 20 years of experience. We are a leading centre for Mohs micrographic surgery to treat skin cancer performing over 1,000 cases of Mohs surgery every year.

We offer photodynamic therapy for some low risk skin cancers.

As a tertiary referral centre for laser treatment to treat certain skin conditions, we offer a comprehensive laser service to treat birthmarks and certain pigmentary conditions.

We are the only hospital in the country using reflectance confocal microscopy on suitable patients, enabling us to view cells and structures of the skin without the need for a biopsy.

Mohs surgery explained

Watch clinicians talk about how Mohs surgery is used to treat skin cancer.

  • Mohs surgery explained – video transcript

    Dr Raj Mallepeddi, consultant dermatologist and lead clinician: Mohs micrographic surgery was developed in the 1930s by Dr Frederick Mohs. It has been refined over the years.

    It is a specialised method of removing skin cancer and aims to achieve the highest likelihood of cure but potentially remove the minimum amount of skin.

    The procedure involves surgically removing skin cancer, layer-by-layer, and analysing each layer of tissue under a microscope until healthy cancer-free tissue around the tumour is reached, called clear margins.

    During the first layer we will mark out the visible part of the tumour with a pen and then inject the area around the tumour with a local anaesthetic.

    This numbs the area so you'll not feel any pain during surgery but will remain awake.

    We may also use an anaesthetic eyedrops if the tumour is near your eye.

    The tumour is then cut out or scraped away, known as curettage, and we then remove a very small margin, usually one to two millimetres, by scoring around the pen line with a scalpel and then cut out the tumour in one even piece.

    This is known as a layer. The surgeon then stains the tissue using special ink so we know exactly which way round it sat on the skin.

    The nurse will then place a secure dressing over the wound and you'll be asked to sit back in the waiting room.

    The marked issue is then sent to the lab where it will be frozen into a block, sliced into fine horizontal sections, and put onto microscope slides. The surgeon then examines them under the microscope.

    If the tissue contains cancer cells, we will remove and examine another layer of tissue in exactly the same way. We repeat this process until the surgeon examines tissue that contains no cancer cells.

    When this happens we know we've removed all the cancerous cells from that site.

    Mohs surgery is unique and so effective because we can evaluate all tissue that is removed and the surgeon can map any tumour to the exact location on the patient's skin.

    This allows all the deepest parts of the tumour to be found accurately and removed.

    Dr Nisith Sheth, consultant dermatologist: After we have removed the skin cancer with Mohs surgery we may carry out reconstruction.

    Reconstruction means fixing the wound that is left after the surgery.

    We normally do this on the same day as the Mohs, but we may need to do it on another day. There are various options for reconstruction.

    These include allowing the wound to heal by itself over a period of weeks, this is safe and can result in a very good appearance but does require care of the wound and dressing changes in the early stages.

    We may be able to pull the edges of the wound directly together with stitches or alternatively we may be able to move or stretch the skin and tissue near the wound to fill it up. This is known as a flap repair.

    This may result in a longer or unusual shaped scar but the final result is often very good.

    We made detach skin from one area, such as behind the ear and place this over the wound stitch it into place. This is known as a graft.

    There may be more than one option for reconstruction and we will discuss this with you to give you not only the best cosmetic result but also the most practical one for your particular circumstances.

    Shared decision-making is very important with this issue and it can help if you're involved by discussing how you'd prefer to repair the wound.

    When you cut the skin there will always be some type of scar, some people heal more easily than others.

    Some scars are more noticeable depending on the location and skin type but we will always aim to ensure the best cosmetic result possible.

    Depending on circumstances, you may have your wound repaired at another hospital or with another team such as plastic surgery.

    In this case you would have a secure dressing in place to go home with until your reconstruction date.

    Dr Emma Craythorne, consultant dermatologist: Mohs micrographic surgery has been recommended to you because your cancer is in an area where we want to reduce the amount of healthy tissue removed such as on your eyelids, your nose, your ears, or your lips.

    It's also recommended if your cancer has been previously treated but has now returned.

    Other surgical techniques can be used to remove skin tumours but this relies on the surgeon being able to see the edge of the tumour clearly with the naked eye and that tumour may be bigger or smaller than the surgeon thinks.

    This can sometimes lead to a larger wound and scar if too much healthy tissue is removed, but more concerning is that it could also lead to too little tissue being removed and the cancer returning.

    The other techniques that are available include, traditional surgical excision whereby the tumour is excised with a four to six millimetre rim of normal tissue around it and the wound is closed, all in one session.

    A quick procedure is scraping and burning of the tumour called curettage and cautery. Neither of these techniques offer as high a cure rate as Mohs surgery and it's not known until one to two weeks afterwards whether all of the tumour would have been removed. They also may cause a larger than necessary scar.

    A non-surgical option for treatment is radiotherapy. This uses high-energy X-rays or similar rays to treat cancer it damages your body cells in the treatment area, killing the cancer cells but allowing your normal cells to recover. Its side effects such as redness and crusting are generally isolated to the area you're having treated.

    Erin Mewton, sister in the dermatological and laser surgery unit: Before surgery you'll have an opportunity to speak to the nurse to discuss the procedure in detail and ask any questions.

    This may happen face to face if you are coming to the hospital for consultation or over the phone if you do not need to attend a consultation before your surgery.

    This is an opportunity to ask about what the procedure entails but also for the nurse to discuss any other health issues you may have and whether or not you take any medication.

    On the day of surgery it's common for people to feel nervous. The nursing staff will ensure that you feel comfortable and well prepared before entering the procedure.

    You're allowed to eat and drink throughout the day as the procedure is performed under a local anaesthetic. We encourage you to bring lunch with you as you'll be asked to stay in the unit until you're ready to go home.

    You'll not spend long in the theatre itself, around 20 or 30 minutes depending on the site and size of the lesion. The rest of the time you'll be sitting in the waiting room.

    It can take up to two hours to get the results back. We also encourage you to come with a friend or family member as you may be on the unit for the entire day.

    After your procedure you have a pressure dressing in place, this is to ensure that the wound is well covered to prevent bruising, swelling and bleeding.

    The nurse will go through any necessary wound care instructions and also give you written information.

    Most patients are medically fit to travel after the procedure, however if you feel unwell or tired it's best to be accompanied and to avoid public transport where possible.

    If there are any concerns when you go home you'll be given a number to phone that puts you through to a nurse.

    If you have a wound repaired with us we will generally ask you to come back in a week's time so that we can look at the wound and remove any stitches.


Mohs surgery: Jeremy’s story

Watch Jeremy as he talks about his experience of having Mohs surgery at our dermatological surgery and laser unit.

  • Mohs surgery: Jeremy's story – video transcript

    When I was very young, as a child in the 1940s, we lived on the coast and my mum was a tremendous believer, as people were those days, of keeping in the sun and I spent much too much of my childhood in the sun.

    I think because I've got fair hair that's what really caused my problems and I think there's an awful lot of people from my generation who have suffered, rather like people in Australia and South Africa who have suffered, because people of that period didn't realise how bad it was to be in the sun so much.

    [Text] Were you well prepared?

    Yeah, they're very good, very good like that. Excellent, yes. And they sort of talk you through everything and, quite rightly, they treat you...they don't treat you as though you're an idiot, but they tell you everything from basics upwards you know. So from that side of things, it's pretty good, or very good, very good. And they always explain to you what they're going to do even though I've been through this routine so many times, they still saying 'now we're going to do this and do that'. And when the whole thing is over they always say to you...tell you what to do and they give you a bit of paper saying what to do when you get home and how to look after the wound and so on and so forth. But as I say, they always brief you beforehand.

    [Text] Jeremy’s day in surgery

    On the day of the surgery I rolled up here and you always have to wait a bit because it's very busy and so on and you read a book or do whatever you want to do. And then one're told the time has come to do the operation on you, and you go in there and one puts on one of those extraordinary gowns that they love in hospitals which I can never get on. You put your arms in first and you have to tie the neck up, you know, and I can never get them on so I always have to get the nurse to do it for me because I'm so stiff. And then you go in and even for just something on your face, which is what I was having, you still have, obviously you take your shirt off and so on, and put this gown on. Really I suppose you go down and lie on one of those medical couches as it were. And they adjust it and make it comfortable and so on. And I always found myself talking away to the doctors and nurses and asking them what they're doing and where they've come from and what their backgrounds are. I quite like talking to them. And then they, I suppose the next stage really is they sort of dab you with various liquids and then they give you an injection and I mean I always find the injection is, again there's nothing to be terribly frightened of. They're so good now, the anaesthetics and they take effect very quickly. I mean I think what people dread is that they sort of jab you and then they sort of prod you with a pin and they say 'can you feel it?' you know after they've put it in. And you say no, and I think what people always dread is that they'll start sawing away and you'll feel it you know, because the anaesthetic won't have worked. But basically I mean one just lies there and, obviously keeping as still as you can and because the anaesthetic is painless but it is, as I say, I found it rather interesting to know what they were actually doing. You need to be quite patient, particularly this big one on my forehead, I mean I can't remember how long it did go on for, but it's a slow business, not so much the actual cutting out of the thing but the sewing you up, it's a very slow intricate needlework. It's like doing a very fine tapestry or something. Fascinating.

    [Text] Is there any discomfort or pain after surgery?

    I sometimes find that these sort of operations that I've been having here for these little rodent ulcers, there's no, they're not uncomfortable or sore or painful after the event. I mean you have to look after them and as I say you have to walk around with these plasters or bandages on you, which is rather embarrassing if they're on your face! But otherwise, certainly it's not painful or uncomfortable or anything like that.

    [Text] Are you happy with the results?

    Very happy, absolutely thrilled. I mean this one on my forehead, I don't know if you can see, but I mean it's extraordinary, it was about that about that size, this flap that they lifted up and then sewed back in. I'm relieved not to have this rather annoying pimple type thing you know? Which was red and sore and occasionally bleeding so it's a great relief to be shot of the beastly thing. They did a wonderful job getting rid of it. I thought they might do something frightful but so far so good! [Laughs]

    [Text] Would you recommend Mohs surgery?

    Yes I mean I would certainly, if people are worried about or wondering about whether to go ahead with this kind of surgery I would certainly say yes for goodness sake do go get good advice and you'll be well looked after and I'm sure you'll benefit from it.



We are the first hospital in the UK to use a new microscope, called a Vivascope, which can detect skin cancer, providing such detailed images that it effectively performs a non-invasive biopsy.

Once validated, it will make it easier and quicker to determine whether moles and skin lesions are a cause for concern. This will:

  • reduce the number of precautionary biopsies
  • provide a diagnosis in uncertain cases - often such lesions are re-examined after three months
  • provide on-the-spot diagnosis - enabling patients to be examined, diagnosed and treated in a single visit
  • ensure there has been complete treatment for conditions suich as lentigo maligna or superical basal cell carcinomas, where topical treatments (medication applied to the skin) have been used.

This is just a small amount of the research we do in this area. If you’re a patient interested in finding out more, then speak to your consultant at your next appointment. If you are not a patient at Guy’s and St Thomas’ then speak to your own consultant in the first instance.


Tel: 020 7188 6407

Email: Gst-tr.

SKIN, a history

Read about Mohs surgery, laser treatment and skin imaging in SKIN, a history using our page turning software or download chapter 4 (PDF 1.91Mb).

Access guides

DSLU in the Cancer Centre accessibility information


My skin cancer meant I needed surgery on my face, I am not a medical expert by any means but I know what was done was brilliant, you can’t even tell

John Pindar, Mohs surgery patient