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MOHS Surgery
MOHS Micrographic Surgery
Skin Cancer Surgery


Mohs Micrographic Surgery to treat skin cancer

Mohs Micrographic Surgery is a specialised surgical procedure to remove certain forms of skin cancers. This page explains what this procedure involves as well as its risks and benefits. If you have any questions or concerns, please speak to your medical professional, or make an appointment for a consultation with our Dermatologists.

Our Dermatologists, Dr Tay Liang Kiat and Dr Sue-Ann Ho are Mohs Micrographic Surgeons.
Dr Tay Liang Kiat, Dermatologist & Mohs Surgeon
Backed by Experience

Here at Dermatology & Surgery Clinic, we have carried out more than 150 cases of Mohs Micrographic Surgery in our clinic and our certified Mohs Surgeons have a combined experience of performing more than 1000 cases of Mohs Surgery.
What is micrographic surgery?

This is a specialised surgical procedure to remove certain skin cancers and is also called Mohs’ surgery after the doctor who developed it, Frederic E. Mohs. Mohs surgery offers high cure rates while maximising the preservation of healthy skin tissue.

During the procedure, the surgeon removes the visible portion of the tumour and subsequently removes further tissue that may have cancer cells, one layer at a time. Each layer of skin tissue is examined under a microscope until all the cancer cells have been removed. A mapping process and colour coding system allows precise localisation of any remaining cancer, with tissue being removed only if it contains cancer, this helps to preserve healthy tissue by minimising removal of surrounding normal skin.
Mohs surgery may be recommended in the event that:

Skin cancer has recurred;
• A tumour was previously removed, but some cancer cells were detected;
• A tumour is detected in an area where the patient wants to preserve as much healthy skin tissue as possible, such as on the eyelids, nose, ears or lips;
• the edges of the detected tumour are not well defined;
• The tumour is of a more aggressive kind.
MOHS Micrographic Surgery Process
Local anesthesia is injected to the treated area to numb it completely, after which the visible portion of the tumor is removed.
A first thin layer of skin tissue surrounding the removed tumor is removed and processed in the lab in our clinic.
The tissue is sectioned and colourcoded with dyes to map out the site of the surgery. The tissue sections are then microscopically examined.
Each thin horizontal tissue section is carefully examined under the microscope for any evidence of cancercontaining cells.
If cancer cells are found in a section, a subsequent thin layer is removed and tested. This process is repeated until there is no evidence of cancer left.
Once the cancer has been completely removed, the wound will be repaired accordingly, usually with a local skin flap or graft.
The advantages of micrographic surgery

Other types of surgery for skin tumours rely on the surgeon being able to see the extent of the cancer. This may lead to a large wound and scar if too much healthy tissue is removed; On the other hand, some cells may contain cancer but are not visible to the surgeon and thus may not be thoroughly removed, causing the cancer to remain or recur. Mohs Micrographic surgery maximises
the chances that a tumour will be completely excised (removed) while preserving the surrounding normal skin.
Are there any other alternatives?
A complete assessment from a dermatologist and a certified Mohs micrographic surgeon is necessary to discuss treatment options and to select a skin cancer management plan, based on the tumour characteristics and patient preferences. Based on various factors including the location or characteristics of the tumour a different removal method may be suitable, such as standard wide excision. However, Mohs surgery is preferred by
patients as it is best for preserving healthy skin and it is also recommended by surgeons if the edges of the tumour are not well-defined or if the tumor is of a high-risk subtype. It is important to note that if skin cancer is not treated, it will continue to grow and may require more aggressive treatment in the future.

If you have any questions or concerns, please speak to your medical professional, or make an appointment for a consultation with our Dermatologists.
How to prepare for Mohs Micrographic Surgery?
Please do not wear any makeup or jewellery on or near the site of the surgery. Speak in detail to your dermatologist/surgeon who will be best able to recommend how you can prepare for your
Getting your consent
If you decide to go ahead with this surgery, you will be asked to sign a consent form after a full consultation. This confirms that you agree to have the procedure and understand what it involves.
What happens during Mohs’ surgery?
There are several stages to Mohs’ surgery. First, the doctor will inject the area where the tumour is, with a local anaesthetic. This numbs the area to minimise any pain during surgery but the patient will remain awake throughout the surgery. If a patient is particularly anxious, we can offer a mild sedative to promote relaxation. Please discuss this with our dermatologists/surgeons.

We may also use anaesthetic eye drops if the tumour is near the eyes.

Once the anaesthetic has taken effect, the visible (also called the clinically evident) part of the tumour is removed, along with a small margin of normal skin tissue. This tissue is taken to a laboratory where the surgeon will be able to look at it under a microscope to check for cancer cells. This takes about 40-60 minutes, so a temporary dressing is applied to the wound while the patient waits.

If cancer cells are present in this tissue, the patient will be brought back into theatre and more tissue will be removed and examined under the microscope. This will be repeated until all the tumour cells have been removed.

The local anaesthetic lasts for about 2 hours, and can be ‘topped up’ if needed. Because of the nature of this surgery, we are unable to say exactly how long the surgery will take.
What happens after the procedure?
Once all the tumour cells have been removed, there are several options for repairing the wound. These will be discussed in more detail before the surgery. The wound may be:
  • Closed by the team who performed the micrographic surgery immediately after the tumour has been removed;
  • Dressed and then repaired by a plastic surgeon at a hospital chosen by our surgeon;
  • Left to heal normally; or
  • Repaired at another hospital. In this case we will renew your dressing before you travel to your referring hospital. We will also give you a letter from our doctors to hand to your surgeon when you arrive at your referring hospital. You will be told how to look after your wound by the team that repairs your wound.
What are the risks?
Your dermatologist/surgeon will explain the potential risks for this type of surgery with you in more detail, but complications include:
  • Bleeding at the site of the tumour.
  • Pain. The local anaesthetic should last until you return home. Aspirin free pain relief (such as Paracetamol) should relieve any discomfort. The doctor or nurse caring for you can give you more advice.
  • Nerve damage. Although your surgeon will try to avoid this, nerves can occasionally be damaged during surgery, leading to a numb area of skin. This is usually temporary.
  • Infection at the wound site. You will be given instructions on how to care for your wound to minimise this risk.
  • Scarring. You will have a scar after the surgery. The doctors use closure techniques to minimise the effect of this. Scars will fade over time.
    What do I need to do after I go home?
    Before you leave the hospital, you will be given full information about how to look after your wound at home.

    You will probably need to rest after the surgery for about 48 hours. If you work, we recommend that you take at least 2 days off after the surgery.
    Is there a follow-up appointment?
    You will have a follow up appointment with the team that repaired your wound.

    If your follow up is with us, we will usually see you one week after your surgery to check that your skin is healing well and to remove any stitches you may have. If there are any changes to this, we
    will advise you on the day of your surgery.

    We usually see you again approximately 1 and 3 months after your wound has healed.


    Skin Cancers

    The skin is the largest human organ. It serves as the interphase protecting the individual from the environment. One of the biggest insult to the skin is ultraviolet (UV) radiation from the sun. UV radiation is a trigger for many skin tumours/growths. Some of these growths are benign and can be left alone. Some however are cancerous and must be removed early. These lesions are called malignant tumours.

    Some common malignant skin tumours are:
    1. Basal Cell Carcinoma (BCC)
    This is the most common malignant skin tumour worldwide. It is a slow growing skin cancer and up to 80% of all BCCs occur on the head and neck especially on the nose. The cancer often presents as a longstanding ulcer with a shiny or pearly raised margin. It is often painless. Chronic sun exposure is a factor in the development of basal cell carcinomas.
    2. Squamous Cell Carcinoma (SCC)
    This is 2nd most common form of skin cancer. It commonly presents as a firm irregular fleshy growth usually on sun exposed skin. The tumour can grow quickly and has the potential to spread beyond the skin. Chronic sun exposure is an important contributing factor in the development of this type of skin cancer. Tobacco products are a significant risk factor for lip and oral SCC.
    3. Malignant Melanoma
    This is a serious form of skin cancer arising from the pigment cells (melanocytes) of the skin.It can occur on any site, including the palms and soles, and it has a tendency to spread to surrounding lymph nodes or other parts of the body. It often presents as a dark brown or black skin growth or ulcer. It may look like ordinary moles but some red flags include:

    Asymmetry in the shape
    Borders irregular
    Colour non-uniform
    Diameter - 6mm
    Evolving (change in shape/ colour/ size)

    Those with a family history of melanoma, or have a history of excessive sun exposure or sunburns are at increased risk of developing melanomas.
    Diagnosis of skin cancers
    Any skin lesion that is progressively enlarging should be assessed and examined by a trained doctor. Contrary to popular belief, malignant skin tumours do not always cause pain, so this symptom is not reliable. If a skin cancer is suspected, your doctor may advise and order a biopsy under local anaesthetic for microscopic examination. Upon confirmation of a malignant skin tumour, the doctor can assess and advise the best option for treatment.
    The most common form of treatment of a malignant skin tumour is surgery. There are 2 surgical options: standard wide excision and Mohs micrographic surgery (MMS). MMS involves surgically removing skin cancer layer by layer like peeling an onion, mapping the excised specimen and examining the entire margins of each layer under the microscope. This facilitates the complete tracing of the tumour roots until healthy, tumour-free tissue is reached.

    MMS thus ensures the highest possible success rate. In fact, reported 5 year cure rates for primary skin tumours treated by MMS is 99% versus 93% for standard excision. Standard surgical excisions involve excising the tumours with a predetermined margin and assessing the excised specimens in the pathology laboratory either with a “breadloaf” or “quandrant” method. These methods leave marginal areas between the sections not microscopically visualised. In fact, it has been shown the above techniques only evaluate about 1% of total margins. The failure to detect subclinical microscopic tumour foci may result in tumour recurrence in spite of “clear” margins on histology report.

    Furthermore, as the tumour roots are being traced and only tumour involved tissues are removed, the technique is also considered to be tissue sparing and is of great value in the excision of tumours occurring in cosmetic sensitive areas like the “H-zone” of the face (around the eyes, mouth and, nose) and the ear, to maximize cosmetic and functional outcome post surgery.

    In addition, as there is greater confidence of clearance of the tumour, the resultant defect can be better managed. Surrounding skin can be mobilized to facilitate closure and hiding the scars at cosmetic subunits junctions, thus achieving better cosmetic outcome.

    In certain situations whereby complete excision may not be feasible, other forms of therapy such as radiotherapy, photodynamic therapy or topical therapy may be used.
    Skin cancer is not uncommon. It ranks among the top 10 cancers among the males and females in Singapore. There is a rising incidence of skin cancer and this can be attributed to the change in lifestyle and behaviour. Early detection and treatment gives the best possible outcome.


    Not sure which treatment is for you? Book your first consultation to discuss your concerns with a member of our medical team.
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