Are moles cancerous? How to tell if your moles may be cancer

14 Feb

Are moles cancerous? It depends on what you mean by “mole”!

Most of our patients think of coloured and/or raised spots on their skin as moles —this means that yes, some “moles” actually are skin cancers.

A skin cancer doctor or a dermatologist thinks of moles and skin cancers as two separate things: a mole isn’t a skin cancer, and a skin cancer isn’t a mole. The difference between moles and skin cancers isn’t always obvious. Sometimes an early skin cancer looks like a mole, and sometimes an odd-looking mole looks like skin cancer.

But when people ask if their moles might be cancerous (a very common question) they aren’t using this strict interpretation.

For the purposes of this page, we consider a mole to be a spot or lump on the surface of the skin, because this is the way our patients tend to think.

Mole removal for benign (non-cancer) spots and lumps is usually a simple procedure which can be achieved with little scarring. Treatment of cancerous moles usually involves surgical excision (cutting out) but other treatments are sometimes used for very early/shallow skin cancers.

Are all moles cancerous?

Very few moles are skin cancers.

In general, a spot or lump on the skin is either a benign lesion (e.g. mole, skin tag, freckle) or a skin cancer from the time it first appears. Common moles and other non-cancer skin lesions don’t usually turn into skin cancers. One exception to this is solar keratoses (actinic keratoses), which sometimes progress to squamous cell skin cancer.

Malignant vs. benign moles

There are many different types of mole.

A “malignant mole” is a skin cancer. When skin cancer is diagnosed at the site of a longstanding mole, what has probably occurred is:

  • The “mole” was in fact a slow-growing skin cancer all along, or
  •  A new skin cancer developed in the same location as the pre-existing mole.
We can’t predict this in advance for any given mole, which means that removing moles doesn’t reduce the risk of skin cancer developing later.

What are the chances of a mole being skin cancer?

Any given mole has minimal risk of being a skin cancer, but there is some information about both the mole and the person that can suggest the risk of one of their moles being a skin cancer.

If the mole is an “ugly duckling” there’s a higher risk of it being a skin cancer.

An ugly duckling mole is one that doesn’t match any of the others on the person’s skin. There’s no specific shape or colour, and it doesn’t even need to be “ugly” — it’s an odd one out or outlier that looks unrelated to the other moles. There’s more information about the ugly duckling rule on our How to check your own skin page.

Examples of how a mole might appear as an "ugly duckling" that doesn't match the other moles

There’s a higher chance that one of your moles could be a skin cancer if you have risk factors. These include:

  • A previous history of skin cancer such as melanoma, squamous cell carcinoma or basal cell carcinoma
  • Many (more than 100) moles
  • History of dysplastic moles
  • Increasing age (by the age of 70, about two-thirds of all Australians have had at least one skin cancer)
  • Very fair skin, especially with red hair
  • History of solarium/tanning bed use
  • Sun-damaged skin, especially if there are solar keratoses present
  • History of multiple peeling or blistering sunburns while young
  • Occupational or other long-term exposure to the sun over many years
  • Smoking

Some general health conditions increase the risk of skin cancer:

  • Taking immune-modifying medications (e.g. for inflammatory bowel disease, rheumatoid arthritis, organ transplant or multiple sclerosis)
  • Some forms of lymphoma or leukaemia
  • History of radiotherapy
  • HIV infection with decreased immunity

When should you worry about a mole?

Some characteristics of a mole might mean that it is more likely to be a skin cancer.

As mentioned earlier, if a mole is an “ugly duckling” it might be more likely to be cancerous.

When examining an individual mole, the ABCDEFG rule can help identify a mole of concern.

A   Asymmetry: If you were to draw a line through the centre of the mole, the two sides would look different.
B   Border: The edge/border of the spot is irregular. It might be clear in one area and indistinct in another.
C   Colour: The spot has many different colours (not just shades of one colour)
D   Diameter: Most melanomas have a diameter greater than 5mm. In general, if the diameter (size from one side to the other) is increasing, it's a suspicious sign.
E / F / G   Elevated, firm, growing: Any raised lump that has a firm consistency and is growing is suspicious.

Warning signs of melanoma

Changes in a mole can be a sign of melanoma, although it's important to remember that there are many reasons why normal moles change and most changes are not due to melanoma or any other  skin cancer.

Changes in size, shape or colour

If a pre-existing mole changes in size (i.e. spreads out sideways), changes from a symmetrical shape to an irregular one, or develops new colours, it can be a melanoma warning sign.

Itching, painful or suddenly raised

A mole that feels itchy, painful or tender to touch may be melanoma, especially if it has changed from being flat to being more raised. Fortunately, most of the time itchy or painful moles are not due to melanoma.

Squamous cell carcinoma and basal cell carcinoma warning signs

Other, more common and less serious skin cancers such as basal cell carcinoma and squamous cell carcinoma may have subtle signs:

  • A pink pimple-like lump
  • A sore (bleeding, scabbed or eroded) that hasn't healed after 3 or more months
  • A crusted raised lump that has grown quickly and is tender to touch
  • An area of rough pink skin that resembles a small rash but hasn’t resolved after applying treatments for dermatitis or infection
  • A small area of rough pink skin that hasn’t settled after being frozen or applying treatments for solar keratosis

What are my options if a mole is cancerous?

Most of the time, if a mole is discovered to be a skin cancer, it isn’t a serious health risk. Nearly all skin cancers diagnosed in a skin cancer clinic are successfully treated.

If a skin cancer doctor or dermatologist suspects that amole might be a skin cancer, the options are:

  • Take a punch or shave biopsy to get more information (e.g. Is the diagnosis really skin cancer? How deep into the skin does it penetrate? Does the growth pattern look aggressive?)
  • Perform a surgical excision to completely remove the mole. This is almost always the better option if your doctor suspects that the mole is a more serious skin cancer such as melanoma or Merkel cell carcinoma.

Treatment options for cancerous mole removal

Once a diagnosis of cancer is confirmed, there are multiple treatment options, each with advantages and disadvantages.

Melanoma and more aggressive sub-types of squamous cell carcinoma and basal cell carcinoma pose a potentially serious health risk and must always be surgically excised (cut out) with a clear margin of normal skin around the edge to prove that the cancer has been completely removed.

Less serious forms of skin cancer can be treated by various surgical or non-surgical methods including:

  • Radiofrequency surgery
  • Electrosurgery, sometimes known as diathermy or electrocautery
  • Curettage (shaving off), followed by cautery of the base of the wound
  • Cryotherapy (freezing)
  • Prescription creams such as imiquimod, fluorouracil or fluorouracil/calcipotriol
  • Photodynamic therapy

For a comparison of these treatments for non-melanoma skin cancers see our blog article Non-surgical treatments for non-melanoma skin cancers.

Arranging a skin cancer check-up with a doctor

A skin cancer doctor or dermatologist can decide whether any given “mole” on the patient’s skin really is a mole, or if it is a skin cancer. This is usually done by examining with a dermoscope. At Spot Check Clinic we take high-magnification photographs of any moles of concern, which allows closer examination of the mole.

In some cases, we use AI-based image recognition or spectroscopic analysis of the mole to get further information about it.

At Spot Check Clinic, a doctor accredited by the Australasian Skin Cancer College can check your moles for signs of cancer.

  • If you are concerned about one or two spots only, and you don’t have skin cancer risk factors, you can usually book an appointment for a 1-3 spot check within 1-2 working days.
  • If you would like to have your whole body checked for signs of skin cancer, book a full body skin check
  • If you have many (hundreds) of moles, you may wish to have total body photography (“mole mapping”) to document them all and help track changes.

If you don’t know which type of skin check or mole check to book, you may find our Which service should I choose? page useful.