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Removal of skin tumours using Mohs micrographic surgical technique

Patient information A-Z

Who is this leaflet for? What is its aim?

One of the doctors or nurses in the dermatology department will have explained to you that you need to have an operation to remove a skin cancer and that this will be performed using the Mohs surgical technique. This leaflet explains the operation and answers some frequently asked questions.

After your operation you will receive a different leaflet providing information including wound aftercare and, if needed, stitch removal.

What is Mohs micrographic surgery?

Mohs surgery is a specialised technique for removing skin cancers. It tends to be used for tumours where it can be difficult to identify the edges (margins) of the tumour and / or to remove as little skin as possible at sites near to the eyes, lips or nose. It differs from other skin cancer treatments in that it allows the immediate and complete microscopic examination of a layer of skin from around the removed cancerous tissue, so that all ‘roots’ or extensions of the cancer can be found and removed. Mohs surgery has been recognised as the skin cancer treatment with the highest reported cure rate for certain tumours although it is important to emphasise that no cancer surgery has a 100% success rate.

Mohs micrographic surgery was developed in the USA by a surgeon called Frederick Mohs, hence the name ‘Mohs surgery’.

The steps of Mohs surgery are:

  1. The area to be treated is cleansed, marked and made completely numb using an injection of local anaesthetic. You will not be asleep (that is, you will not have a general anaesthetic) but you will be in an operating theatre.
  2. The visible cancer is removed first and then a thin layer of adjacent tissue from around and beneath the wound. The wound is dressed and you return to the waiting room while the tissue is being processed. You may eat and drink during this waiting time.
  3. The specimen is processed while you are waiting. This allows it to be examined under the microscope to check if the tumour has been completely removed and the margins are clear. This is often the most time-consuming part of the procedure, usually requiring over an hour to complete.
  4. If the margins are not clear, you will be asked to return to the operating theatre and the consultant will remove additional tissue only at points where the cancer is present.
    If your anaesthetic has worn off, the consultant will give you a further local anaesthetic injection. This second piece of tissue will be processed and examined. This process is repeated until all the cancer is removed. Please be aware that this process may take the entire day.
  5. Once the consultant confirmed all the cancer is removed, you will be asked to return to the operating theatre to discuss the best way to close the wound.

What should I do before the operation?

If you are pregnant, please contact the clinic for advice (01223 216091).

Please ensure you inform us of your medications and any drug allergies.

If you are taking warfarin, please arrange for an INR blood test one to five days before the operation.. INR results are given as a number (for example 2.3) and the condition you are taking it for has a required therapeutic range that your doctor tries to keep you within (e.g. 2.0-3.0 but sometimes higher). We prefer for your INR to be 3 or lower before we operate. However you should not let your INR drop below your therapeutic range as this puts your health at risk so please do not adjust or stop taking your warfarin without discussing this with your prescribing doctor. We simply want to avoid a very high INR during surgery but we do not require it to be below the required therapeutic range. If the INR is very high, we may need to postpone the operation until another date, so please phone 01223 216091 if your INR is above 3.

If you are taking aspirin or clopidogrel prescribed regularly for your heart or circulation, or an oral anticoagulant (such as rivaroxaban or dabigatran) you may or may not be advised to stop the tablets.
Please do not stop taking any medication before discussion with a doctor.

Please avoid non-steroidal anti-inflammatory drugs (such as ibuprofen), aspirin (unless prescribed - see note above) and all aspirin-containing medicines, such as some cold and flu remedies, for seven days before and for two days after your surgery. Certain herbal remedies also thin your blood so please stop these two weeks prior to surgery. If you have a pacemaker or defibrillator you must inform us of the type as we may need to check this before the operation. Please phone 01223 216091 to inform the surgical coordinator.

What should I do on the day of the operation? What should I bring with me?

Please bring a list of your current medications with you on the day of your operation.

On the day of surgery please take any regular medications (unless you have been told otherwise) and eat a normal breakfast. We suggest you wear loose fitting, comfortable clothes. You may wish to bring a friend or relative to accompany you and drive you home following surgery, although they are not routinely permitted to be in the operating theatre during the operation (please check with clinic 7 during COVID pandemic as visitors may not be allowed in hospital). You may also wish to bring something for lunch, a snack and drink and something to read to occupy your waiting time. We also recommend you bring paracetamol with you.

All operations will take place in one of the theatres in Clinic 7, Level 3, Addenbrooke’s Hospital. Please report to the clinic reception desk when you arrive.

If you have a pacemaker / defibrillator you must inform the doctor before the operation starts.

How long does the procedure take?

In most cases, the Mohs procedure can be completed in three or fewer stages totalling less than eight hours. However, as it can be difficult to predict how extensive a cancer will be, we ask that you reserve the entire day for surgery. Very occasionally, the surgery is not completed in one day and then arrangements will be made to complete the operation on another day.

What happens after Mohs surgery is completed?

When the cancer is completely removed, the consultant will discuss the options of wound closure with you. Options include:

  • Allowing the wound to heal naturally, without additional surgery (which may produce the best cosmetic result). In this case the wound will require regular dressing until it is completely healed. This will be performed by hospital staff, your own practice nurse or sometimes yourself or a family member.
  • Wound closure using stitches. For small wounds, direct closure by suturing the wound from side to side may be possible. However, in certain areas on the face where there is very little tissue that can be stretched (e.g. nose, ears, around the eyes) a skin graft or skin flap may be necessary. A skin flap is when the skin adjacent to the wound is partially cut free, and then rotated or advanced to cover the wound, with stitches then placed to hold the flap in its new position. When a graft is required, skin from another area such as the neck, behind the ear or over the collarbone is cut free and sutured above the wound. The original site is closed with stitches or allowed to heal on its own.
  • Referral back to the original surgeon or to another specialist surgeon for wound repair.

Benefits of Mohs surgery

Treating skin cancer with Mohs surgery might be used when:

  • it is not clear where the tumour begins and ends
  • the tumour is close to important structures such as the nose, lips or eyes
  • the tumour has recurred despite previous treatment

In these cases Mohs surgery is considered to allow the maximum preservation of healthy tissue and complete microscopic examination of the margins around the tumour resulting in a high cure rate.

Risks of Mohs surgery

Patients should understand that there is no absolute guarantee that any given procedure will be totally free of complications or adverse reactions. The risks of Mohs surgery are generally the same as for other surgical procedures carried out on the skin such as ‘ordinary’ skin lesion removal and suturing. These are the sort of problems that may occur with skin surgery:

Post-surgical discomfort

Local anaesthetics are usually effective for about two hours. Most patients do not complain of significant pain after the procedure. If there is some discomfort, normally only paracetamol tablets are required for relief. Some patients may find that the surgical area remains tender for several weeks or months after the operation, especially if large amounts of tissue were removed.

You may experience some bruising and swelling around the wound, especially if the procedure is performed near the eye area. This will clear in a week or two.


It is normal for a small amount of blood to come through the dressing. Any heavier bleeding can be stopped by applying firm pressure to the dressing for 15 minutes. If bleeding continues, you should contact your GP or this department.


Rarely, a wound can become infected, and this will show up as increased pain, swelling and redness of the wound after a few days. If you are concerned that the wound may have become infected, please contact your GP or this department for advice. In some cases the consultant carrying out the Mohs surgical procedure will prescribe antibiotics for you to take after the operation.


Any form of surgery will leave a scar. The length, type and width of the scar will depend on the type of wound closure performed. If the wound was closed using stitches, the stitch line is likely to be red initially but this redness usually fades over a period of weeks to months.

Nerve damage

During surgery tiny nerve endings are cut, which may produce a temporary or permanent numbness in or around the surgical site. If a large tumour is removed or extensive surgery is required, occasionally a nerve or muscle may be cut resulting in temporary or permanent weakness in a portion of the face. This is, however, an unusual complication.

Need for further surgery

Skin grafts and flaps used to cover surgical wounds may occasionally not fully survive, in which case additional surgical repair might be required later on. Additionally, the appearance of raised or roughened scars may be improved by surgical or non-surgical techniques some weeks or months after the initial procedure.

What should I do or not do after the operation? Can I drive home afterwards?

We recommend that you have a companion to escort them home. Patients should not drive after surgery to the face area, as will often be the case in Mohs surgery.

Depending on the type of wound closure performed you may have a number of stitches and a dressing. You will need to keep the wound and dressing dry for 48 hours. This may make it difficult to have a bath or a shower during this time.

Any stitches will usually need to be removed either by the nurse at your GP’s practice or in the hospital clinic between five and ten days after the procedure. Please let us know before your operation if you anticipate that this may be a problem.

You should avoid activities such as cycling, swimming, other strenuous exercise, bending, straining or lifting heavy objects for at least 14 days following the procedure.

Smoking has been shown to have an adverse effect on wound healing after surgery. We would therefore recommend that you do not smoke for two weeks after your operation.

Alternatives to Mohs surgery

It is important to understand that there are alternative treatment options to Mohs surgery when removing a skin cancer. Your doctor or nurse will generally have discussed these with you in clinic when the diagnosis of a skin cancer was suspected or confirmed. Alternative treatment options may include:

  • local radiation (radiotherapy)
  • conventional surgical removal of the tumour
  • chemotherapy creams or injections
  • cryosurgery (deep freezing)
  • photodynamic therapy (which uses a type of light and a light-activated chemical called a photosensitiser).

Depending on the type, localisation and extent of your skin cancer, some of the above options might not be suitable in your case.

Contacts / further information

Should you have any further questions about your procedure, please feel free to ask us when you come to the hospital for it. Alternatively you can contact the clinic nurses on 01223 216091. However, if after reading this leaflet you are unsure if Mohs surgery is the right option for you or would like to revisit the alternative treatment options listed above, please contact us prior to attending your Mohs appointment.

References / sources of evidence

We are smoke-free

Smoking is not allowed anywhere on the hospital campus. For advice and support in quitting, contact your GP or the free NHS stop smoking helpline on 0800 169 0 169.

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Contact us

Cambridge University Hospitals
NHS Foundation Trust
Hills Road, Cambridge

Telephone +44 (0)1223 245151