Margin control surgery

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Sometimes a skin cancer can extend under the skin surface where no one can see it. This can be a problem. The tumour might be excised with a healthy rim of apparently normal tissue only to find that the pathologist says there is still tumour at one edge.

This can happen with any type of skin cancer and in any location. But there are certain types of tumours and certain locations where we know there is a greater risk of unexpected tumour being found at the margin of the excised specimen.

Examples of types of tumour that frequently creep under the surface beyond where they can be seen:

• Lentigo maligna - an early from of melanoma, often growing on the face
• Difficult BCCs - Basal cell carcinomas that have aggressive characteristics and extend deep into tissues. These include sclerosing, morphoiec, micronodular, infiltrating and desmoplastic BCCs. Your doctor will know whether your BCC is one of these more concerning types.
• Larger skin tumours

Examples of locations where tumours more commonly burrow beneath the surface:

• Highest risk - Nose, ear, eyelids
• Intermediate risk - Elsewhere on the face

Margin Control Surgery

As such, there are times when simply estimating where to cut and close through routine skin examination is not ideal. In selected cases we adopt a more scientific approach. Commonly the tumour and its apparent margin are removed but the defect not closed immediately. Rather we then wait and see whether all is clear under the microscope. The careful fine sectioning of the cancer are especially checked under the microscope for any tumour at or near the margin of the specimen. This is where the term "margin control surgery" comes from.

If this examination is all OK, the defect is reconstructed. If the microscope examination indicates an area of concern, then that area is further excised and the new specimen subjected to the microscope. This process continues until there is certainty that there is no microscopic evidence of tumour at the margins. Only then is the defect  closed.

Types of Margin Control Surgery

There are two main types of this careful and methodical approach to difficult skin cancers. The first is called Mohs surgery. It is named after Dr. Fred Mohs who first described the technique in USA. In Mohs surgery, the microscope slides are prepared very quickly using a so called "frozen section" technique. If a 2nd stage of excision is required, it will usually be undertaken the same day.

The alternative approach involves specimens being processed and examined by a slower "urgent paraffin section" approach. After the first excision, the patient  goes home and returns a few days later. At that time either reconstruction or a further stage of excision is effected as appropiate. Again the process continues until there is microscopic evidence of tumour clearance. This approach is sometimes called "Slow Mohs".

There is no evidence that one technique is superior to the other. They are both effective and have their relative advantages and disadvantages. The first is very common in USA. The second is more common in Europe. Both are used in Australia.

Alternatives?

There are alternatives to margin control surgery that still allow the doctor a more scientific approach to accurately determine the true extent of a difficult skin cancer.

Delineating curettage. This technique was pioneered by dermatologist and ACSCM member, Dr. Tom Connelly in Florida USA. It involves carefully scooping out the tumour and visualizing it in three dimensions before complete excision. This technique has proved to be very effective and Dr. Connelly will soon be publishing a trial of this methodical approach. Many ACSCM members have adopted this established technique.

Dermoscopy. Skin surface microscopy is also a useful adjunct in estimating the true extent of any deep tumour spread. This involves placing a small surface microscope on the skin to identify abnormal changes beneath the surface.

Confocal microscopy. An expensive and as yet unavailable modality that in essence obtains microscope images of the skin before any excision.  This may have a role in the future. It is not used anywhere in Australia or New Zealand to our knowledge.

You doctor will consider your tumour type, details and location before discussing with you when he / she considers one of these methodical approaches is in your best interests.

Other questions about skin cancer management?