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Specialist Advice — 8 minutes

Shining light on skin cancer: the facts on melanoma

Raymond Lepage, PhD, Doctor in Biochemistry
Raymond Lepage, PhD, Doctor in Biochemistry
Science popularizer

Your skin is your body’s largest organ [1]. The skin prevents water loss, regulates body temperature and protects us against infection [2]. It contains many different types of cells, including keratinocytes, basal cells, and melanocytes. Each of these can eventually show abnormal growth leading to skin cancer.

Is the sun the only cause of skin cancer?

Skin cancer is most frequently associated with skin exposed to the sun (the face, back, scalp, lips), but it can also appear in non-sun exposed areas (palms and soles, beneath the fingernails or toenails, genitals). This indicates that there may be other contributing risk factors contributing, such as exposure to toxic substances, or a weakened immune system [3].

Skin cancer is the most commonly diagnosed cancer worldwide. We’re most familiar with melanoma, which begins in the melanin-forming cells that control our skin’s pigment. Although non-melanoma cancers (squamous cell carcinoma and basal cell carcinoma) are by far the most frequent types of skin cancer, they generally show slow growth, rarely spread, and are easily treatable. Melanoma represents only 4% of all skin cancers but is responsible for 80% of deaths from skin cancer [4].

Where does melanoma come from?

Melanoma starts in melanocytes, cells that produce the pigment (melanin) responsible for the colour of our skin, hair and eyes. Melanin is a protective agent against more deleterious sun effects [5]. When melanocytes are exposed to UV radiation they release melanin, which is taken up by keratinocytes to cause the tanning effect. Too much of this radiation, however, can lead to cell mutation in melanocytes cells and cause melanomaskin cancer.

It is therefore not surprising that non-caucasian individuals with more melanin-producing skin cells show a much lower incidence of skin cancer [6]. It is also not surprising that individuals with very pale skin, freckles, light eyes and red hair are the most sensitive to UV-damage leading to skin cancer [7]. Among caucasian individuals, those living in countries closer to the equator like New Zealand and Australia show the greatest risk of developing skin cancer [8].

What are the stages of melanoma?

There are four stages of melanoma development. In Stage I, the disease is localized to a specific area of the skin. Fortunately, the majority of diagnoses are done at this early stage when the condition is more treatable. In Stage II, the disease is more developed, but still localized. In later stages, the cancer first spreads to the lymph nodes (Stage III) and finaly to distant organs (Stage IV). As with any other cancer, the sooner the cancer is diagnosed, the better the chances of cure or at least keeping the disease under control.

I have a weird mole. When should I consult my physician?

A melanoma often starts as a mole anywhere on the skin. Most people have a few moles, but although not entirely specific, the first sign of a possible melanoma is a change in the colour, size or shape of an already present or new mole.

Cancer Canada suggests the ABCDE rule to help you look for other common signs of melanoma skin cancer.

Letter Signification Definition
A Asymmetry One-half of a mole does not have the same shape as the other half.
B Border The edge of a mole is uneven (irregular). It can look jagged, notched or blurry. The colour may spread into the area around the mole.
C Colour The colour of a mole is not the same throughout. It could have shades of tan, brown and black. Sometimes areas of blue, grey, red, pink or white are also seen.
D Diameter The size of a mole is larger than 6 mm (1/4 inch) across, which is about the size of a pencil eraser.
E Evolving There is a change in the colour, size, shape or feel of the mole. The mole may become itchy or you may have a burning or tingling feeling.

Do not hesitate to see your doctor if you have any of these changes on your skin.

More specific information can be found on the Canadian Cancer Society website. There are also now some apps available for your smartphone that may help you identify problematic moles with your camera.

Treatment of melanoma

Treatment options depend on many factors including the size, type, depth and location of the mole or lesion and your personal preference. Small skin cancers may not require treatment beyond an initial skin biopsy which removes the entire growth. Surgery option, including local excision, sentinel lymph node biopsy, complete lymph node dissection, or surgery for metastases remain the treatment of choice for most melanoma skin cancers. As with many other cancers, immunotherapy, radiation or chemotherapy and targeted therapy with biologicals are the main ancillary treatments after surgery.

Prevention, prevention, prevention!!!!

Skin cancer is caused almost entirely by sun exposure. It should be evident that protecting our skin from sun exposure is the most efficient (and most economical!) means of preventing melanoma skin cancers. According to Canada Public Health Services, the following recommendations should keep you protected when the UV index is at 3 or higher, indicating a significant risk.

Protect your skin:

  • Cover up – wear light-coloured, long-sleeved shirts and pants, a hat made from breathable fabric, and sunglasses with UVA and UVB protection
  • Limit your time in the sun – stay out of the heat between 11 and 3.
  • Use a sunscreen labelled “broad spectrum” with an SPF of at least 30 and preferably water resistant
  • Avoid using tanning equipment. There is no such thing as a healthy tan, and any tanning equipment will damage your skin in the same way that the sun will.
  • Ask your doctor, nurse or pharmacist if any of the medications you are taking could be harmful to you if you are exposed to UV rays.
  1. Goldsmith, L. A. "My Organ Is Bigger than Your Organ." Archives of Dermatology 126, no. 3 (1990): 301-02. [PUBMED]
  2. "Skin Cancer." CancerQuest. Accessed July 24, 2019.
  3. "Skin Cancer." Mayo Clinic. February 20, 2019. Accessed July 24, 2019.
  4. Miller, Arlo J., and Martin C. Mihm. "Melanoma." New England Journal of Medicine 355, no. 1 (2006): 51-65. doi:10.1056/nejmra052166. [PUBMED]
  5. Meredith, Paul, and Tadeusz Sarna. "The Physical and Chemical Properties of Eumelanin." Pigment Cell Research 19, no. 6 (2006): 572-94. doi:10.1111/j.1600-0749.2006.00345.x.[PUBMED]
  6. Crombie, I. K. "Racial Differences in Melanoma Incidence." British Journal of Cancer 40, no. 2 (1979): 185-93. doi:10.1038/bjc.1979.165.
  7. "Skin Cancer." CancerQuest. Accessed July 24, 2019.
  8. Matthews, Natalie H. "Epidemiology of Melanoma." Cutaneous Melanoma: Etiology and Therapy [Internet]. December 21, 2017. Accessed July 24, 2019.