Melanoma: When is a mole more than a mole?
The term “mole” is the common name for a skin lesion often called a “melanocytic nevus”, but can also be broadly applied to any dark-colored skin lesion (brown, tan, or skin-colored) that has a sharp border. The lesions are more often than not completely benign — and not melanoma — and often referred to as birthmarks if present at birth or beauty marks. Nevi can be classified in many ways but most easily are thought of as congenital (present at birth) or acquired (develop later in life sometime). They can present as a variety of colors and can be flat, raised, or even produce hair. There are many other “named” types of moles but most are harmless and are given names by location, microscopic findings, or physical characteristics.
Most moles have a very small chance of converting to melanoma, a form of skin cancer, however a significant number do arise from a mole. This risk is higher if you have numerous acquired moles (> 50) or you have a mole that has been present since birth (congenital nevus). The risk of conversion to a melanoma depends on a lot of factors, such as size of the mole, genetics, and sun/UV exposure. Certain families harbor genes that create lots of moles and a higher chance of skin cancers. People in this category need to be vigilant to avoid the sun and have routine skin examinations.
Congenital moles are removed for a number of reasons. The most important is to decrease the risk of developing skin cancer. This risk is proportional to the size, therefore congenital nevi as classified based on size: small (< 1.5 cm2), medium (1.5 – 20 cm2), and Giant (> 20 cm2). Small nevi have a lifetime risk of melanoma of 1 to 5%. These can often be observed and biopsied if there are any changes noted. If the lesion is in a difficult place to monitor (on the back or hidden by clothes) then it is reasonable to remove, even if benign. Medium-sized nevi have an intermediate risk of conversion to melanoma but rarely do before puberty. If there is concern – removal any time before puberty is appropriate. The increased size of these lesions can make them unsightly. In certain locations (i.e. face) they may cause problems with social interactions. Many parents choose to have them removed around school age to avoid teasing. Giant nevi are sometimes hairy or have a rough surface. If they are over the middle of the back they may involve the underlying spine. Giant nevi have a 5-10% lifetime risk of melanoma with 50% of these cases between 3 to 5 years of age. For this reason giant nevi should be removed as early as feasible.
Acquired nevi are usually not treated until adulthood since they have a lower chance of malignancy. Anything that is atypical or changing should be biopsied. The characteristics I look at for determining if something should be biopsied are the “ABCDE’s”: Asymmetry, Border irregularity (most have smooth border), Color variegation (anything more than 1 solid color), Diameter more than 6 mm (size of pencil eraser), or Evolution (changing). I always recommend a “punch” or “excisional” biopsy of a portion of the nevus over a “shave” since this allows the pathologist a better look at the depth of the lesions. One a biopsy is done you forever lose the accuracy of the depth measurement which is critical for determining prognosis and treatment. This does sometimes require a dissolvable stitch but often heals without any noticeable scar and gives better information. Unsightly lesions that are obviously non-cancerous can be burned to remove but have a chance of coming back, and there is the possibility of “missing” something. There are laser and topical treatments that can lighten moles however this does NOT reduce risk, and this cosmetic treatment should be used very cautiously so that you don’t delay treatment of potential malignancy.
If something on pathology shows up then you may have the entire lesion removed to either cure the cancer or reduce the risk of it developing cancer. These can spread to other organ systems (bone, lungs, lymph node, etc.) and result in death, so should not be taken lightly. If you think you have a mole that is changing or fits one of the above criteria you should seek treatment from a dermatologist, plastic surgeon, or other provider skilled at evaluating these lesions. The two best things you can do for your skin is protect yourself from sun exposure either by covering up or wearing sunscreen and regularly checking the entire body for new or changing moles.