Introduction

Over 3 million skin cancers are diagnosed globally each year.¹ The skin is the largest organ of the body, and as such, clinicians have faced the challenge of accurately diagnosing and removing cancer, whilst simultaneously maintaining the beauty and functionality of your skin.

After years of research and development, Mohs surgery – a procedure so meticulous that it not only targets cancerous lesions but leaves the smallest possible scar and spares the healthy tissue - has become significant in the world of dermatology and skin cancers. This article will tell you what you need to know about Mohs surgery.

Basics of skin cancer

Skin cancers can be broadly categorised into melanoma skin cancers and non-melanoma skin cancers.¹

Imagine you’re basking in the warm glow of the sun, and you notice a new spot on your skin; a dark spot that looks like a mole but perhaps bigger or less uniform in colour. Whilst this does not necessarily mean it’s something cancerous, melanomas can present similarly to this.

Melanomas are the result of abnormal growth and proliferation of melanocytes, cells which are responsible for pigmentation. It is important to know that melanocytic lesions can be benign or malignant. Benign tumours do not metastasise to invade other parts of your body, whereas malignant melanomas are cancerous and pose the risk of metastasis. The extent of the tumour growth and local tissue invasion (including lymph node involvement) will vary depending on each case.

The non-melanoma skin cancers category involves several types: the most common being Basal Cell Carcinomas (BCCs) and Squamous Cell Carcinomas (SCCs). It is believed that incidence rates for non-melanoma skin cancers are both outdated and underreported.¹ Despite this, BCCs are the most common type of skin cancer in the UK, followed by SCCs.

The development of non-melanoma cancers does not involve melanocytes, so such lesions will not usually present with increased pigmentation (except in more rare forms such as pigmented BCCs). BCCs and SCCs commonly occur in sun-exposed areas, such as the face. Of the different types of BCCs, nodular BCCs are the commonest, and they present as nodules with pearly, rolled edges, surrounding telangiectasias, and often have a depressed centre. In some cases, they may bleed as they can be sensitive to minor trauma.

While BCCs usually arise due to mutations that affect the basal cell layer of the epidermis, SCCs occur due to mutations in squamous keratinocytes in the epidermis. The main cause of this cancer type is chronic ultraviolet exposure (particularly UVB). It is true that sun and UV exposure predominantly affects individuals with pale fair skin tones (Fitzpatrick skin types I and II in particular), however amongst individuals with brown and black skin shades (Fitzpatrick V and VI), SCC appears to be the commonest.²

The characteristic features of SCCs include firm lesions that are crusting, bleeding ulcerating and may be painful. If the cancer is confined to the epidermis (i.e., the top layer of the skin), it is known as Bowen’s disease. Because this can progress to become invasive SCC, Bowen’s should be treated promptly. If there are precancerous scaly lesions on the skin, it may be actinic keratosis. This is an important differential diagnosis, as actinic keratosis has a 10% risk of developing into an SCC.²

All lesions will require appropriate examination and investigation, prior to diagnosis. Also, it often occurs that the diagnosis of a lesion is unclear, based on physical skin examination, so surgical procedures can have both a diagnostic and therapeutic role.

Understanding Mohs surgery

Mohs surgery, also known as Mohs micrographic surgery provides a 99% cure rate for skin cancers that have not been treated before.³ This impressively effective procedure was initially developed by Frederic E. Mohs, in the 1930s. Later in the 1960s, Perry Robins, recognised that Dr. Mohs’ ‘unpopular’ procedure should be implemented into the field of dermatology, as it had great potential. Today, Mohs surgery is the gold standard approach for many types of skin cancer. This surgery may also be named “margin controlled excision” in some resources, as it’s an alternative way of describing the procedure.

The surgery is performed in stages, but in one visit, so patients will not need multiple appointments for their tumour excision. After re-examination of the lesion, the doctor will mark the area which will have the lesion to be excised. Local anaesthetic is applied to the marked area of skin – this will ensure that the patient does not feel pain from sharp instruments, but the patient will remain awake throughout the surgery.

The procedure proceeds by removing the top layer of the lesion. This means that the surgeon will remove the visible layer of the lesion, usually the raised part. This does not mean that the cancer has been excised, as some tumours can present as “tip of the iceberg”, which means that they might be extending deeper or wider into the tissue than we can visibly see.

The next essential step is to analyse the sample piece of skin obtained. The surgeon may cut the obtained tissue into separate pieces, apply dyes to colour code and map out the surgical site for reference. This is immediately sent to the lab to be examined but would take some time. During the wait, your wound will be temporarily bandaged or dressed, to allow you to relax.

Microscopic examination of the obtained tissue will identify if there are any remaining cancer cells and where they would be in the surgical map. If the pathologist identifies a need for more excisions, another layer is removed, in the same way as described previously. The excised margins will be analysed, and the process may be repeated several times, until there are no more cancer cells identifiable.

Depending on the site and location of the surgery, some wounds may be left to heal (particularly if the procedure was not repeated several times). Usually however, the wounds would be stitched, with little to no complications. In some cases, reconstruction with a skin flap from neighbouring tissues or even a skin graft may be indicated. Other specialist surgeons may be present if the procedure is more complicated or requires reconstruction, e.g., a plastic surgeon.⁵

Who can have Mohs surgery?

Mohs micrographic surgery is indicated in many skin cancers, including recurring tumours, cancers that have not been completely removed and cancers in areas that require important cosmetic or physical consideration e.g., eyes, lips and nose.⁵

Conventional surgery is also another approach to excising skin cancers. Depending on the complexity of the case, Mohs may not be the preferred treatment option. You may find that Mohs is a common procedure for non-melanoma skin cancers (e.g., BCCs and SCCs), but for melanomas this may not often be the case.⁴

The reason for this is melanomas are staged based on depth and penetration into layers of the skin, with potential to be more aggressive and metastasis. Mohs surgery is usually limited to treating superficial skin layers and might be more challenging for the deeper melanomas. As lymph nodes are another important consideration in melanomas, the current gold standard approach for melanoma removal and staging is a standard conventional surgical excision and lymph node biopsy dissection.

Complications of Mohs surgery

Like all surgeries, Mohs micrographic surgery has potential complications.

Firstly, it is possible that the treatment will not be as effective as anticipated, and therefore would not fully remove the cancerous tissue.

Secondly, there may be a risk of bleeding or bruising. Wound infections are also an important consideration. Whilst they are unlikely, in present practice, it is important to follow the doctors’ advice to avoid wound infection and take any prescribed antibiotics to avoid further complications.

Lastly, there is a risk of nerve damage, and this depends on the surgical location. Numbness in the area is expected during the procedure and may take time to improve (up to several months), but if this does not improve or you have concerns about this, contact your doctor to discuss the issue promptly.⁵

Summary

Mohs micrographic surgery, also known as margin-controlled excision, is a common and effective procedure for basal cell carcinomas and squamous cell carcinomas. This surgical approach aims to remove the skin cancer and leave as much healthy tissue as possible and the smallest possible scar. Consequently, this cemented Mohs surgery as a powerful and effective approach to dealing with cancers within the field of dermatology.