Melanoma skin cancer is the most serious form of skin cancer in Canada. It starts in melanocytes — the cells that give your skin its colour. When these cells grow out of control, they can spread to other parts of the body. The good news is that melanoma skin cancer is highly treatable when caught early.
What Is Melanoma Skin Cancer?
Melanoma begins when pigment-producing cells called melanocytes become abnormal. These cells then grow uncontrollably and invade surrounding tissue. Unlike other skin cancers, melanoma can spread quickly if left untreated.
Melanoma is less common than other types of skin cancer, but it is by far the most dangerous. However, when doctors find it early — while it is still on the surface of the skin — the cure rate is very high. In more advanced stages, melanoma skin cancer can spread through the blood or lymph system to organs, bones, and the brain.
Common Causes of Melanoma Skin Cancer
The most important cause of melanoma skin cancer is exposure to ultraviolet (UV) radiation. UV rays damage the DNA inside melanocytes. Over time, this damage can trigger abnormal cell growth. Here are the main causes:
Sun exposure: UV radiation from the sun — especially between 10 a.m. and 3 p.m. — is the leading risk factor for melanoma.
Tanning beds: Indoor tanning equipment also emits UV rays and significantly raises your risk.
High altitude exposure: UV radiation is stronger at higher elevations, making outdoor workers and hikers more vulnerable.
Ozone layer thinning: Experts estimate that every 1% reduction in the ozone layer leads to a roughly 1% increase in melanoma cases.
Family history: Having multiple family members with melanoma raises your personal risk.
Weakened immune system: People who have had organ transplants, or who live with leukaemia or lymphoma, face a higher risk.
For more information on UV safety in Canada, visit Health Canada’s sun safety guidance.
Warning Signs: The ABCD Rule for Melanoma
The most important warning sign of melanoma skin cancer is a change in a mole or skin spot. You should watch for changes that develop over a period of one month to two years. A helpful tool is the ABCD rule, which helps you identify suspicious changes at home.
A — Asymmetry
One half of the mole does not match the other half. A normal mole is usually symmetrical. If you fold it in half mentally, both sides should look roughly the same.
B — Border
The edges of the mole are ragged, notched, or blurred. Healthy moles tend to have smooth, even borders. Irregular or uneven edges can be an early warning sign.
C — Colour
The colour is uneven or has multiple shades. You may notice a mix of brown, black, and tan. Red, white, or blue patches within the mole are also a concern. A colour that spreads from the edge of the mole onto the surrounding skin is a particularly important early sign of melanoma skin cancer.
D — Diameter
The mole is larger than 6 mm across — about the size of a pencil eraser. Any mole that is growing in size should be checked by a doctor, even if it is smaller than 6 mm.
Other Symptoms to Watch For
Beyond the ABCD rule, there are other changes that may signal melanoma skin cancer. These include:
A flat mole that suddenly becomes raised or thickened
Redness, swelling, or small new coloured spots appearing around a larger mole
Itching, tingling, or a burning sensation in or around a mole
A mole that becomes soft, crumbly, or bleeds easily
An open sore on the skin that does not heal
Melanoma can develop on an existing mole or on a completely normal patch of skin. It most often appears on the chest and back in men, and on the legs in women. Less commonly, it can grow on the palms, soles, under the fingernails, or on mucous membranes inside the mouth or rectum.
It is important to know that other skin conditions — such as seborrhoeic keratosis, warts, and basal cell carcinoma — can look similar to melanoma. Therefore, always get a professional opinion rather than trying to self-diagnose.
How Melanoma Spreads
Melanoma skin cancer is classified as either primary or metastatic. Primary melanoma is confined to the skin. With early treatment — usually surgery — most primary melanomas are curable.
Without treatment, melanoma rarely goes away on its own. In most cases, it spreads to other parts of the body. Doctors call this metastasis. Metastatic melanoma travels through the lymph system or the bloodstream to reach organs such as the brain, lungs, or liver.
The long-term outlook for primary melanoma depends on two key factors:
Depth of invasion: How deeply the melanoma has grown into the layers of the skin.
Ulceration: Whether the surface of the tumour has broken down into an open sore.
Metastatic melanoma is much harder to treat. This is why early detection is so critical. The Mayo Clinic’s overview of melanoma provides a detailed look at staging and treatment options.
Signs That Melanoma Has Spread
If melanoma skin cancer has reached other parts of the body, the symptoms can be harder to recognize. They may include:
Swollen lymph nodes, especially in the armpits or groin
A lump or thickened area under the skin
Unexplained weight loss
Grey or darkened skin tone (a condition called melanosis)
These symptoms can have many causes. However, if you notice any of them — especially alongside skin changes — it is important to speak with a healthcare provider right away.
Who Is at Risk?
Melanoma skin cancer can affect anyone. However, certain factors increase your risk. These include:
A history of sunburns, especially blistering burns in childhood
Fair skin, light hair, or light eyes
Many moles, or unusual (dysplastic) moles on the body
A personal or family history of melanoma
Working outdoors or spending a lot of time in the sun
Using tanning beds, especially before age 35
Living at high altitude or near the equator
Having a suppressed immune system
In Canada, people who work outdoors — including construction workers, farmers, and postal carriers — face higher levels of UV exposure over their lifetimes. This makes regular skin checks especially important for these groups. The World Health Organization’s fact sheet on ultraviolet radiation explains how UV exposure contributes to skin cancer risk globally.
When to See a Doctor About Melanoma
If you notice any of the ABCD warning signs, or any new or changing skin spot, do not wait. Book an appointment with your family doctor as soon as possible. Early detection saves lives.
If you do not have a family doctor, a walk-in clinic can assess suspicious moles and refer you to a dermatologist if needed. Most provincial health plans in Canada cover visits to your family doctor or walk-in clinic for skin concerns. Your doctor may refer you to a specialist for a biopsy if a mole looks unusual.
You should also do a full-body skin self-exam once a month. Use a mirror to check hard-to-see areas. Ask a partner or family member to help with areas like your back and scalp. Early action is the single most effective way to improve your outcome with melanoma skin cancer.
Always consult your family doctor or a qualified healthcare provider before making any decisions about your health. This article is for informational purposes only and does not replace professional medical advice.
Frequently Asked Questions About Melanoma Skin Cancer
What does melanoma skin cancer look like in the early stages?
In its early stages, melanoma skin cancer often looks like an unusual mole or dark spot on the skin. It may be asymmetrical, have uneven borders, contain multiple colours, or be larger than 6 mm. Using the ABCD rule regularly can help you spot changes before they become serious.
Can melanoma develop on skin that has no moles?
Yes, melanoma skin cancer can develop on completely normal skin with no existing mole or mark. In fact, many melanomas appear on areas of skin that previously looked healthy. This is why it is important to inspect all areas of your skin regularly, not just existing moles.
Is melanoma skin cancer hereditary?
Melanoma can run in families. If you have two or more close relatives who have been diagnosed with melanoma, your personal risk is higher than average. However, most cases of melanoma occur in people with no family history. Tell your doctor if melanoma has appeared in your family so they can recommend more frequent screening.
Does sunscreen actually prevent melanoma skin cancer?
Regular use of broad-spectrum sunscreen with SPF 30 or higher can significantly reduce your exposure to UV radiation, which is the leading cause of melanoma skin cancer. Sunscreen works best as part of a broader approach that includes wearing protective clothing, seeking shade, and avoiding peak sun hours between 10 a.m. and 3 p.m.
How is melanoma diagnosed in Canada?
In Canada, melanoma is typically diagnosed through a skin biopsy. Your family doctor or a dermatologist will remove a small sample of the suspicious skin and send it to a lab for analysis. Most provincial health plans cover this process, so speak with your family doctor or visit a walk-in clinic if you have a concerning mole.
What is the survival rate for melanoma skin cancer?
When melanoma skin cancer is caught early and treated before it spreads, the five-year survival rate is very high — often above 95%. However, once it has spread to distant organs, treatment becomes much more difficult and outcomes are less predictable. Early detection is by far the most important factor in improving survival.
Key Takeaways
Melanoma skin cancer is the most dangerous form of skin cancer, but it is highly treatable when found early.
UV radiation from the sun and tanning beds is the leading cause of melanoma.
Use the ABCD rule — Asymmetry, Border, Colour, Diameter — to monitor your moles at home.
Melanoma can appear on normal skin, not just on existing moles.
If melanoma spreads to other organs, it becomes much harder to treat — early action matters.
Canadians can see their family doctor or visit a walk-in clinic if they notice any suspicious skin changes. Most provincial health plans cover these visits.
Protect yourself with sunscreen, protective clothing, and shade — especially during peak UV hours.
Always speak with a healthcare professional if you are concerned about a mole or skin change.
