How to distinguish between a mole and a melanoma?

A mole, or nevus, is a flat or raised spot that appears on the skin's surface. It's the result of an accumulation of melanocytes in the superficial layer of the epidermis. Most moles form in response to repeated exposure to UV rays: that's why congenital nevi, or moles present at birth, are so rare. They can also be triggered by hormonal changes, during adolescence or during pregnancy for example. Moles are generally benign but they should be closely monitored as they can evolve and become dangerous.

In rare instances, moles can evolve into melanoma, an aggressive form of skin cancer.

Melanomas are cancerous tumors that develop within melanocytes. They can form directly on the skin, but in 20 to 30% of cases, they form in an existing mole, according to a study conducted by STRATIGOS and his team. Heredity plays a key role in the development of certain skin cancers. A genetic mutation, often on the BRAF gene, can be the cause, leading to excessive activation of the MAPK signaling pathway, involved in cell growth. Sun exposure is also a factor in the occurrence of melanomas. Indeed, according to the National Cancer Institute, about 80% of melanomas result from excessive exposure to UV rays.

The emergence of a mole and that of melanoma do not follow the same rules or timeline. Moles typically form during childhood or adolescence, and their number tends to stabilize in adulthood. Some may appear later, but this is less common. It's worth noting that individuals with light skin, eyes, or hair generally have a greater number of moles.

The situation is different for melanomas. Although they can appear at any age, the average age of diagnosis is 60 years old. That's why the late development of a pigmented lesion is something to closely monitor. However, it's important to emphasize that melanomas are not only relevant to older individuals: it remains the most common cancer in adults between 25 and 50 years old in western regions.

Even though it's not always easy to distinguish a mole from a melanoma, their appearance is slightly different. A typical nevus usually has a well-defined shape, with clear and regular edges and a uniform color. It can be brown, black, sometimes slightly bluish, but its color is consistent across its entire surface. The surface of a mole is normally smooth, without significant texture or irregularities. Moreover, nevi are painless and do not cause itching sensations.

Melanoma, on the other hand, has a much more heterogeneous appearance. Its borders can be poorly defined and its shape is often asymmetrical. Moreover, a melanoma can sometimes be of different colors: this chromatic diversity is indicative of an abnormal proliferation of melanocyte cells. Another sign to watch for: a melanoma can be granular, rough, or present raised areas. Some lesions may even ooze, bleed spontaneously, or form a crust, which is not the case with a benign mole. Finally, unlike a nevus, a melanoma tends to evolve and grow quickly, often beyond 6 mm in diameter. When faced with a lesion presenting one or more of these characteristics, a prompt consultation with a dermatologist is essential.

Advice : To identify atypical moles that may develop into melanoma, it is advisable to refer to the ABCDE method.

While self-monitoring of moles is crucial, only a dermatologist can definitively confirm whether a pigmented lesion is a mole or a melanoma.

During a consultation, the dermatologist begins with a detailed clinical examination of the skin, assessing the size, shape, color, and texture of pigmented lesions. To delve deeper, they often use a dermatoscope, an optical instrument similar to a magnifying glass that allows for the observation of the internal structures of the mole with magnification. This reveals elements invisible to the naked eye, such as vascular irregularities or structural asymmetries, which could be a sign of malignancy. If a lesion appears concerning, a biopsy is performed, meaning a skin sample is taken for subsequent laboratory analysis under a microscope.

In the event of a confirmed melanoma, the approach relies on a surgical excision. The goal is to completely remove the tumor with a safety margin around the melanoma to reduce the risk of recurrence. If the cancer is at a metastatic stage, meaning it has spread, immunotherapy or, less commonly, chemotherapy, may be performed to enhance the immune response and halt the progression of the melanoma.

Early detection makes all the difference: a melanoma diagnosed early is much easier to treat than a metastatic melanoma.

• BONIOL M. & al. Reviews on sun exposure and artificial light and melanoma. Progress in Biophysics and Molecular Biology (2011).

• HATZISTERGOS K. E. & al. How, and from which cell sources, do nevi really develop? Experimental Dermatology (2014).

• BOSENBERG M. & al. Melanocytic nevi and melanoma: unraveling a complex relationship. Oncogene (2017).

• STRATIGOS A. J. & al. A review of nevus-associated melanoma: What is the evidence? Journal of the European Academy of Dermatology and Venereology (2022).