Melanoma is a type of skin cancer. Many risk factors have been linked to the disease, but one major cause is avoidable - overexposure to the sun.
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What is melanoma and skin cancer?
Melanoma is a particular form of skin cancer. It happens when the pigment cells (the melanocytes) become cancerous. Most pigment cells are found in the skin, although melanoma can also occur in the eyes (ocular melanoma) and other parts of the body.1
There are numerous types of skin cancer, of which melanoma is one of the common types, although it is much less common than basal cell and squamous cell skin cancers. Melanoma is a rarer but more dangerous type of skin cancer than these because it is more likely to spread. It is very rare in people with dark skin.1,2
This article focuses on melanoma because it is the best known and most important skin cancer to prevent. Also, much of the information about melanoma, including in terms of treatment, also applies to the more common, but less worrying, skin cancers and pre-cancerous lesions.2
Briefly here, however, squamous cell skin cancer and basal cell skin cancer are both a type of non-melanoma skin cancer. Basal cell is the most common form, usually grows very slowly, and usually never spreads. Neither does squamous cell usually spread. Both types are also known as keratinocyte skin cancers - to do with their appearance under the microscope - and both are linked to sun exposure.2
Fast facts on melanoma
Here are some key points about melanoma. More detail and supporting information is in the body of this article.
- Melanoma is one of three common types of skin cancer, and the most dangerous form.
- Melanoma is rare compared with the other two common skin cancer types.
- Numerous risk factors have been identified for melanoma.
- Repeated overexposure to the sun is the only avoidable risk factor - not getting sunburnt is the best prevention against melanoma.
- Diagnosis of skin cancer is made initially by the appearance of the skin, and confirmed by biopsy sample.
- Self-monitoring of moles and other markings on the skin helps to detect skin cancer early.
- Treatment usually aims to completely remove skin cancer tumors, and is curative if done at the cancer's earliest stage.
Melanomas can develop on any part of the skin. Certain areas are more prone than others, however - in men, the trunk (chest and back) is most likely to be affected by melanoma; in women, legs are most commonly affected. Other common sites are the neck and face.2
Skin cancer is the most common type of cancer in the US, says the National Cancer Institute.1
Almost 70,000 Americans are diagnosed with melanoma every year, and almost a further 50,000 cases are diagnosed with an early form of the disease.1
Recent developments in melanoma
Did a risk of skin cancer drive the evolution of black skin in humans? Skin cancer has influenced skin color, according to research in February 2014.
What causes melanoma?
As with all cancers, the causes of melanoma are being continually researched. Certain types of skin are more prone to melanoma than others. The following are risk factors that make people more prone to skin cancer:2,3
Change of appearance in skin moles should raise suspicion of melanoma.
- High freckle density or tendency to develop freckles after sun
- High number of moles
- Five or more atypical moles
- Presence of actinic lentigines (small gray-brown spots also known as liver spots, sun spots, or age spots)
- Giant congenital melanocytic nevus (brown skin marks present at birth - birth marks)
- Pale skin that does not tan easily and burns; light-coloured eyes
- Red or light-coloured hair
- High sun exposure, particularly if it produces blistering sunburn, and especially if sun exposure is intermittent rather than regular
- Age - risk increases with age
- Family or personal history of melanoma
- Being female
- Having an organ transplant.
Only one of the above risk factors stands out as avoidable - high sun exposure and sunburn. A report by the World Health Organization has estimated the number of early deaths caused by excessive exposure to the sun's UV (ultraviolet) radiation: 60,000 around the world in the year 2000, and many of these people died from melanoma.4
Avoiding overexposure to the sun, and sunburn, are, therefore, obvious ways to prevent unnecessary cases of skin cancer. Sunbeds are also a source of damaging UV exposure.2
Recent developments in melanoma
Multiple sunburns as an adolescent increase melanoma risk by 80%. May 2014 research found that severe sunburn incidents between the ages of 15 and 20 were linked to higher risk of melanoma.
Signs and symptoms of melanoma
As with other forms of cancer, the early stages of melanoma may not produce any symptoms - which is why active surveillance is heavily promoted by cancer charities and so on. Some signs, however, may signal the disease, and changes in skin appearance are the key ones (these are also used in the diagnostic process).
The Melanoma Research Foundation has produced a web page that compares pictures of melanoma with those of normal moles. The American nonprofit organization also lists the following symptoms and signs that should prompt suspicion of skin cancer - plus a visit to the doctor:5
- Skin change - a new spot or mole, or a change in color, shape or size of a current spot or mole
- Skin sore that fails to heal
- Spot or sore that becomes painful, itchy, tender or bleeds
- Spot or lump that looks shiny, waxy, smooth or pale
- A firm red lump that bleeds or appears ulcerated or crusty
- A flat, red spot that is rough, dry or scaly.
The ABCDE examination of skin moles is also a key way to reveal suspect lesions.
Melanoma tests and diagnosis
Most cases of melanoma affect the skin, usually producing changes in existing moles.5 For this reason, it is possible to detect the early signs of melanoma by self-examining moles and other pigmented blemishes and freckles regularly, looking for any changes in their appearance.
Remember that moles can be found on the back and so should be examined, too, perhaps with the help of a loved one.2
Cancer doctors are most concerned with lesions that 'stand out from the crowd'3 - and they describe five simple characteristics to look out for in the ABCDE of melanoma appearance:1,6
- Asymmetric: whereas normal moles are typically round and symmetrical, one side of a cancerous mole is likely to look different from the other side - not round or symmetrical
- Border: this is likely to be irregular rather than smooth - ragged, notched or blurred
- Color: melanomas tend not to have one color but uneven shades and colors, with varying black, brown and tan color, even perhaps other colors such as white or blue
- Diameter: there has been a change in the size of the mole, and it is typically larger than a normal mole, more than a quarter inch in diameter
- Evolving: the mole's appearance has changed over a period of weeks or months.
The American Academy of Dermatology (AAD) has produced a poster to help with the above method of how to spot skin cancer.7
The AAD also offers a body mole map for self-monitoring skin.
Doctors may score appearance in a similar way, to rate their suspicion of skin cancer and determine the need for urgent referral to a cancer specialist.3
The higher the score, the greater the suspicion, although just one point is enough to take action if there is any concern about cancer. Scoring three points or more on the following results in a strong suspicion of skin cancer:3
- Two points for each of the following 'major' features of a lesion: change in size, irregular shape or border, irregular color
- One point for each of the following 'minor' features: largest diameter is 7mm or more, inflammation, oozing or crusting of the lesion, change in sensation (including itch).
Doctors may use microscopic or photographic tools to help them visualize a lesion.2 If a doctor suspects a diagnosis of skin cancer, the patient will be referred urgently to a cancer specialist, and a biopsy will be arranged to test the lesion - taking a sample for examination in the laboratory. A biopsy may be taken by the primary care doctor themselves but usually by the specialist receiving the urgent referral.1,3,6 There are four types of biopsy:1,6
- Shave: some of the tissue is scraped away with a thin, sharp blade
- Punch: a circular plug of tissue is removed
- Incisional: tissue is removed by scalpel
- Excisional: the whole lesion is removed - typical if the lesion is a suspected melanoma.
The choice of biopsy will depend on the size and location of the lesion, among other factors.2
As with other types of cancer, testing of skin cancer also indicates the stage of the cancer.2
Staging describes how advanced the disease is - how widespread the cancer is. Staging provides doctors with treatment guidance. The American Joint Commission on Cancer recommends the TNM staging system for skin cancers:2
- T score from 0 to 4 based on the thickness of the tumor
- N score from 0 to 3 based on how nearby lymph nodes are affected
- M score based on metastasis (spread) to other parts of the body.
The above is a brief summary of staging a cancer diagnosis, but oncologists work with much more complex detail.2 Staging becomes more relevant if there has been spread from the primary melanoma.
Treatment and prevention of melanoma
The treatment of skin cancer is similar to that of other cancers, except that the aim of skin cancer therapy is invariably to completely remove it, which is possible because of its location. Therefore, surgery is the most common treatment for skin cancer.1
A melanoma is often surgically removed at the same time as a biopsy is taken for testing. Otherwise, the specific surgical operation involves removal of the lesion and some of the normal tissue around it - a border or margin around the tumor or suspected tumor.2
Other, less common treatments for skin cancer include chemotherapy, photodynamic therapy (light and drug therapy, but not usually against melanoma), biological therapy (drugs that work with the immune system), and, although not usually, radiation therapy.2
Getting outside in the sun is important because it enables our bodies to produce vitamin D, without which we get conditions such as rickets and osteomalacia.3 Sensible sun exposure is advised.
Repeated episodes of severe sunburn increase the risk of melanoma.
Avoiding becoming burnt while enjoying the sun safely offers the benefits of vitamin D without creating undue risk of skin cancer.
It takes less time to get enough sun than it does to get sunburnt, and some people need to produce more vitamin D - for example, people:3
- With naturally brown or black skin
- Who cover their whole body and head with clothing
- Who stay indoors all the time
- Who are pregnant
- Who are vitamin D-deficient and breastfeeding.
Avoiding excessive exposure to the sun and ultraviolet light, and therefore reducing cancer risk, is achieved by:3
- Avoiding sunburn
- Wearing clothes that protect from the summer sun
- Using sunscreen with a minimum sun protection factor (SPF) of 15, but preferably SPF 20-30, with 4- or 5-star UVA protection
- Not spending longer in the sun because sunscreen is used
- Liberally applying sunscreen about half an hour before going out, and applying it again after half an hour.
- Reapplication should then be every two hours to maintain adequate protection
- Avoiding the highest sun intensity between 11am and 3pm, by finding shade. Outdoor workers need to take particular care
- Protecting children by trying to keep them in the shade, with clothing, and by applying SPF 50+ sunscreen
- Keeping babies out of direct sunlight.
Doctors recommend that tanning booths, lamps, and sunbeds are not used.3
Recent developments on melanoma treatment and prevention
Starving melanoma cells may slow tumor growth. Research published in The International Journal of Cancer in January 2014 found a way to block cancer cell access to glucose.
Sunscreen alone "not enough" to protect against melanoma. Researchers publishing their findings on mice in Nature in June 2014 conclude: "UV light has long been known to cause melanoma skin cancer, but exactly how this happens has not been clear. These studies allow us to begin to understand how UV light causes melanoma."
Written by Markus MacGill