How Do Melanomas Form?

  • Medical Author: Jeffery John Meffert, MD
  • Medical Editor: Melissa Conrad Stöppler, MD
    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

Ask the experts

How do melanomas form?

Doctor's response

A changing skin spot may be a problem, but not every change means cancer. A mole may appear and then get bigger or become raised but still be only a mole. It is normal for many moles to start flat and dark, become raised and dark, and then later lose much of their color. This process takes many years.

Most public-health information about melanoma stresses the so-called ABCDEs:

  • Asymmetry: One half of the mole is different from the other half.
  • Border irregularity: The spot has borders which are not smooth and regular but uneven or notched.
  • Color: The spot has several colors in an irregular pattern or is a very different color than the rest of one's moles.
  • Diameter: The spot is larger than the size of a pencil eraser (6 mm).
  • Evolving: The mole is changing in size, shape, color, or overall texture. This may also include new bleeding.

These guidelines are somewhat helpful, but the problem is that many normal moles and other benign lesions of the skin are not completely symmetrical in their shape or color. This means that many spots, which seem to have one or more of the ABCDEs, are in fact just ordinary moles and not melanomas. Additionally, some melanomas do not fit this description but may still be spotted by a primary-care physician or dermatologist. Not all melanomas have color or are raised on the skin. Amelanotic melanomas have little or no color to the naked eye and may be confused with traumatized benign nevi or basal cell carcinoma. Desmoplastic melanoma may appear to be a thickened area of skin like a scar. These are treated the same way as more typical melanomas but, in the latter case, may be more difficult to determine the exact margins of the tumor.

As a rule, melanoma is not painful unless traumatized. They sometimes itch, but this has no diagnostic or prognostic importance.

The more rapid and dramatic the skin change, the less serious the problem.

When changes such as pain, swelling, or even bleeding come on rapidly, within a day or two, they are likely to be caused by minor trauma, often a kind one doesn't remember (like scratching the spot while sleeping). If a spot changes rapidly and then goes back to the way it was within a couple of weeks, or falls off altogether, it is not likely to represent anything serious. Nevertheless, this would be a good time to say once again: Nobody can diagnose him- or herself. If one sees a spot that looks as though it is new or changing, show it to a doctor. If one see a spot that doesn't look like one's other spots, it should be evaluated.

How can people estimate their level of risk for melanoma?

Individual sunburns do raise one's risk of melanoma. However, slow daily sun exposure, even without burning, may also substantially raise someone's risk of skin cancer.

Factors that raise one's risk for melanoma include the following:

  • Caucasian (white) ancestry
  • Fair skin, light hair, and light-colored eyes
  • A history of intense, intermittent sun exposure, especially in childhood
  • Many (more than 100) moles
  • Large, irregular, or "funny looking" moles
  • Close blood relatives -- parents, siblings, and children -- with melanoma

The presence of close (first-degree) family with melanoma is a high risk factor, although looking at all cases of melanoma, only 10% of cases run in families.

Having a history of other sun-induced skin cancers, such as the much more common basal cell or squamous cell carcinomas, indirectly raises one's risk of melanoma because they are markers of long-term sun exposure. The basic cell type is different, however, and a basal cell or squamous cell carcinoma cannot "turn into melanoma" or vice versa.

The best way to know one's risk level is to have a dermatologist perform a full body examination. That way one will find out whether the spots one has are moles and, if so, whether they are abnormal in the medical sense.

The medical term for such moles is atypical. This is a somewhat confusing term, because among other things the criteria for defining it are not clear, and it's not certain that an atypical mole is necessarily precancerous. Patients who have lots of "atypical moles" (more than 24) do have a higher risk for developing melanoma but not necessarily within one of their existing funny-looking moles. It may be a challenge to find the "baby melanoma" in the middle of a back full of large, dark, or irregular moles. If someone has such moles, a doctor will recommend regular surveillance and may recommend biopsy of the most unusual or worrisome looking moles.

Sometimes, one learns at a routine skin evaluation that one does not necessarily need annual routine checkups. In other situations, a doctor may recommend regular checks at 6-month or yearly intervals.

For more information, read our full medical article on melanoma symptoms, treatment, staging, and prognosis.

REFERENCES:

"Melanoma: Clinical features and diagnosis"
UpToDate.com

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Reviewed on 10/3/2017