Ask the expert: MELANOMA

Summer has officially arrived in the northern hemisphere, and when those elusive hot days grace us, a lot of us spend a lot more time in the Sun. Protecting ourselves from the Sun’s harmful UV-rays is something that is diligently advised because of the carcinogenic nature of the damage caused in sunburn.

Melanoma is one of the deadliest skin cancers, and sun damage is its major cause. To find out more about this type of skin cancer, we’ve been given the opportunity to ask an expert from the field of dermatopathology.

Today’s expert is Dr James Carton.

Dr Carton is a consultant histopathologist at Imperial College. He has been a specialist dermatopathologist since qualifying, and reports the full range of inflammatory and neoplastic dermatopathology, including alopecia cases. He is also the author of the Oxford Handbook of Clinical Pathology, part of the world renowned Oxford Medical Handbook series.

And so we begin:

What is melanoma?

“Melanoma is a malignant melanocytic neoplasm. Melanocytes are the melanin-producing cells found in the skin. Melanin is a pigment which acts to protect the skin from UV radiation.  The term melanoma always implies a malignant tumour.”

What are the incidences of melanoma based on race/skin type?

“Melanoma is predominantly seen in fair skinned individuals in whom it is about 20 times more common than darker skinned individuals.”

Have we seen increases in incidence of melanomas relating to the depletion of the ozone?

“Ozone depletion is believed to be one contributory factor in the increasing incidence of melanoma.”

What is a Dermascope? Is one used in diagnosing melanomas?

“A dermascope is a tool that allows detailed examination of a skin lesion by using a magnifier and polarised light to eliminate reflections off the skin surface. It’s primary use is the examination of pigmented skin lesions for the early detection of melanoma.”

Are there different types of melanomas?

“Yes. Traditionally melanoma has been subclassified into four major subtypes: superficial spreading melanoma, lentigo maligna melanoma, acral lentiginous melanoma and nodular melanoma. More recently there has also been a move towards a molecular classification of melanoma  which groups melanoma based on shared genetic abnormalities. These groups include: melanomas arising on chronically sun damaged skin; melanomas arising on non-chronically sun damaged skin; melanomas arising on UV protected sites; melanomas arising without associations to epithelial structures.”

What, if anything, determines the prognosis of a melanoma?

“Unlike many malignant tumours, melanomas are not graded histologically. The most important prognostic factor is the maximum thickness of the melanoma which is measured microscopically and is known as the Breslow thickness.”

A table showing the Breslow thickness classification and its relationship with approximate 5-year survival.

Can you get a melanoma on parts of the skin that are not exposed to the Sun?

“Yes, melanomas can arise on relatively sun protected sites e.g. the sole of the foot. These types are the most common type of melanoma seen in people of African descent.  Rarely, melanomas can also arise at mucosal sites such as the vulva, anal canal, nose, oesophagus, and also in the eye.”

I’ve read that some melanomas are a result of a mutation in the BRAF gene. Is it the Sun that causes this mutation, or is it just a faulty gene the person is born with?

“BRAF mutations are most commonly seen in the non-chronically sun damaged types of melanomas (about 70% of these types). UV radiation is the most likely mutagen.”

Do immunohistochemical tests help confirm a diagnosis of melanoma?

“In most cases the diagnosis of melanoma is made on morphological grounds on H&E stained sections. Sometimes immunohistochemistry is useful to confirm a malignant tumour is melanoma, particularly in the case of a metastatic deposit where  other types of malignant tumours may be a consideration. The vast majority of melanomas stain with the markers S100 and MelanA.”

Do melanomas have a tendency to spread to other sites of the body?

“Melanoma is a highly malignant tumour with capacity for widespread metastasis to lymph nodes and visceral organs including the lungs and liver. Melanoma is also one of the malignant tumours that shows a particularly propensity to metastasise to the brain.”

What is the treatment for melanoma?

“The mainstay of initial treatment is complete excision of the melanoma by wide local excision. Some patients may also be offered a sentinel lymph node biopsy to check for the presence of microscopic metastatic disease in the regional lymph node draining the site of the melanoma.  Patients with metastatic melanoma may be offered a variety of treatments including chemotherapy, immunotherapy and biological therapy (the latter includes vemurafenib for melanomas that demonstration mutation in the BRAF gene).”

A table showing the guidance for clear (tumour-free) margin excision according to the size of the malignant melanoma lesion.

We hear all the time about using creams to protect us from Sun damage, but is there anything else we can do to protect us? Is there anything about our diet that can help?

“Exposure to UV radiation is by far the biggest risk factor for the development of melanoma. Adequate sun protection is therefore the most important modifiable risk factor.”

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A huge thank you to Dr Carton for his time participating in this month’s Ask The Expert.

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If you have any further questions about melanoma, or would like to have some more information about the questions above, Dr Carton has generously offered to answer your queries for the next month. So, please do make the most of this great opportunity to ask him your questions about melanoma. You can submit your question(s) a number of ways:

•  post in the comments box below

• @reply on twitter to me at (@dellybean) or (@HistoQuarterly)

•  or email me using the contact button on my homepage.

We look forward to hearing from you.

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Useful links

Use the ABCD rule for detecting a melanoma yourself.

A type of melanoma was featured in a previous HistoQuarterly. See here for a detailed histological description of the Superficial Spreading Malignant Melanoma.