Melanoma is a type of cancer that occurs in the melanin producing cells (melanocytes) of the skin. The skin is the body’s largest organ, and its job is to protect the body from injury, infection and damaging UV light. It also helps to regulate body temperature, and manufactures vitamin D. Melanin is the pigment that gives our skin colour.
Melanoma occurs when the cells acquire a genetic mutation, which causes them to rapidly divide and multiply out of control.
In 2017, it’s estimated that 7,200 new cases of melanoma will be diagnosed. The lifetime risk of developing melanoma in Canada is 1 in 57, and the average age at diagnosis is 59 years. Found early which it often is, melanoma is a highly treatable disease with an excellent cure rate.
Causes and Risk Factors
Exposure to ultraviolet (UV) radiation from sunlight or tanning lamps and beds increases the chances of developing melanoma. A single blistering sunburn doubles the risk of melanoma. UV B light is known to cause cancer by altering the DNA in skin cells. However, UV A is more likely to cause damage to melanocytes, leading to melanoma.
Risk factors for melanoma include a prior diagnosis of melanoma, family history, multiple atypical moles, rare inherited genetic mutations such as CDNK2A, the inability to tan, and fair skin that sunburns easily. Caucasians who have blonde or red hair, blue eyes, or freckles are at higher risk of developing melanoma.
All atypical moles or moles that exhibit changes should be checked by a dermatologist or nurse specialist. Self-examinations are helpful in catching early signs. The “ABCDE” rule is a memory prompt that details the 5 warning signs:
A: Asymmetry – irregular shape of the mole
B: Border – the edges of the mole look uneven, ragged
C: Colour – shades of black, brown, tan, pink or other colours visible
D: Diameter – larger than 6mm (size of pencil eraser)
E: Evolving – changes in size, shape, appearance, texture, or colour, or growing in an area of previously normal skin
Melanoma is usually painless and first appears as a change in the size, color, shape, or texture of an existing mole. Other suspicious changes may include scaliness, itching, changes in texture, spreading of pigment from the mole into the surrounding skin, oozing or bleeding. Melanoma can also develop on previously normal-appearing skin.
Types and Prognosis
Melanoma is the most serious type of skin cancer. Although it represents the smallest percentage of all skin cancers, it has the highest number of deaths. Survival depends on the depth of the lesion and the extent of its spread at diagnosis.
A normal mole is usually uniform in shape and colour with a distinct border separating it from surrounding skin. Most people have about 10 to 40 moles and majority of these develop before the age of 20. Larger moles with irregular borders, and multi colours are called dysplastic nevi. After puberty, these moles are much more likely to turn into malignant melanoma than are normal moles.
Superficial spreading melanoma is the most common type and represents 70% of all melanomas. It’s most often found on the legs, chest and back. It is slow growing initially. Superficial spreading melanoma is often flat and irregular shaped, and is black and brown in colour.
The second most common type is nodular melanoma, a faster growing type of melanoma. It’s most often found on the chest, back, neck and head. If not removed, it can quickly spread and become dangerous. It begins as a raised area of dark black, blue or red colour. Occasionally nodular melanoma is flesh-coloured.
Other less common types include lentigo maligna melanoma, more common in older individuals who have had over exposure to sun over a period of many years, and acral lentiginous melanoma. The latter is quite rare, and can occur on the hands, soles of the feet or within nail beds.
Scientists believe that hidden varieties of melanomas suggest a strong genetic predisposition to the disease even in the absence of exposure to sun. When melanoma occurs in individuals with darker complexions, it is most often in hidden areas such as between the toes, on the palms, soles, scalp or genitals.
Subungual melanoma is a rare form of melanoma that occurs on the nail bed. It appears as a brown or black discoloration that can be mistaken for a bruise. If this type of discoloration takes more than two months to heal or starts spreading to involve the cuticle, a dermatologist should immediately be involved. It is at this stage the disease is most treatable.
Melanomas in the mouth, digestive tract, urinary tract or the vagina also occur. These are harder to detect and symptoms are often mistakenly attributed to other ailments. For example, a melanoma in a woman’s vagina may cause itching and bleeding—which could be attributed to a yeast infection or menstrual irregularities.
Ocular melanoma occurs in the pigment-containing cells in the retina. These melanomas can only be detected during regular eye exams as they do not produce any symptoms. On the other hand, melanomas that occur in the conjunctiva (lining of the eyelid) or the choroid (pigmented coating within the eyeball) may cause a scratchy feeling under the eyelid or dark spots in the vision. Wearing sunglasses that block 99 to 100 percent of UV A rays prevents the development of ocular melanoma.
When melanoma spreads to distant sites it is most often to the lungs, liver, brain, GI tract, bone and adrenal glands.
Because it is so often caught early, melanoma has an excellent cure rate. The 5-year relative survival rate is a high 89%.
Diagnosis and Medical Work-up
Everyone should perform a monthly skin self-exam to help familiarize you with your moles, freckles and birthmarks so that changes can be easily spotted.
In individuals who are at high risk, if melanoma is suspected, a general practitioner or specialist conducts a thorough skin examination looking for abnormal changes in the pigmented areas of the skin. In some cases a diagnostic tool called dermoscopy is used to examine a lesion before a biopsy is performed. This tool is capable of magnifying a skin cell up to 10 times in size.
Once an abnormal lesion is found, a skin biopsy is performed. All or part of the suspicious lesion is removed and the sample is sent for analysis. If the lesion is small in size, an excisional biopsy (either a punch or an elliptical excision) which involves the removal of the entire growth along with a small border of normal-appearing skin, is performed. An incisional biopsy removes the most irregular part of a growth, and is used for larger moles.
A non-invasive device called the Aura Device visually scans a mole or lesion to determine if it’s cancerous. Raman spectroscopy capable of analyzing chemical reactions in the skin is used to provide instant accurate results. This can reduce the number of unnecessary biopsies, and decrease wait times for skin cancer surgery.
Once you have received a diagnosis of melanoma, the pathologist examines the thickness and depth of the cancerous lesion. Imaging techniques such as x-rays, CT scans, MRIs, or PET scans are also performed to determine the extent of the disease and inform the most appropriate treatment.
Melanoma can be treated through surgery, chemotherapy, radiation and biologic therapy.
The purpose of surgery is to remove the tumour in its entirety. Early-stage melanomas are often removed completely during the biopsy and require no further treatment. Surgery for more invasive melanomas involves cutting out the cancer along with a large border of normal skin— a wide local incision. In these cases, a skin graft (taking skin from another part of the body) may be performed to replace the skin that is removed.
Systemic chemotherapy prevents cancer cells from dividing throughout the body, while regional chemotherapy directs chemicals to specific sites, avoiding damage to normal cells. If melanoma is found on an arm or leg, chemotherapy may be regionally delivered as a hyperthermic isolated limb perfusion.
Radiation therapy directs high beam x-rays at the targeted site to kill cancer cells. It is used for small tumours, and to destroy cancer cells remaining after surgery.
Biologic therapy deploys the body’s immune defenses to fight the cancer, using re-conditioned lymphocytes from the patient.
Targeted therapy targets specific genes, proteins and tissue of the cancer to inhibit the growth and spread of the cancer. This type of therapy may be used to treat metastatic or inoperable melanoma with a BRAF V600E genetic mutation.
- Canadian Cancer Society
- Melanoma Network of Canada
- Canadian Skin Cancer Foundation
- Canadian Dermatology Association
- CBC News Health