Melanoma–threatening nevi are pigmented benign neoplasms of the skin that have the greatest risk of malignancy and degeneration into malignant melanoma. There are several varieties of such moles that differ in appearance, age of appearance, histological structure and other factors. Diagnosis of melanoma-threatening nevi is carried out by examining the neoplasm and histological examination of tissues obtained as a result of its removal. Treatment of formations in most cases is surgical, the degree and volume of intervention depends on the type, structure and size of the mole. In the future, dispensary observation by a dermatologist or oncologist is required.
Melanoma–threatening nevi are several types of benign pigmented skin formations that quite often degenerate into melanoma. According to medical statistics, such neoplasms are a fairly common condition – their share among moles of all types is about 10%. At the same time, the incidence of melanoma is much lower – about 2 cases per 100,000 population, which indicates that melanoma-threatening nevi do not always lead to the development of a malignant tumor. Nevertheless, their presence significantly increases the risk of this disease and significantly potentiates the influence of carcinogenic factors of various nature. For this reason, in dermatology, the presence of melanoma-threatening nevi is considered a rather serious condition that requires medical measures and supervision by a specialist for the timely detection of melanoma.
The causes of the development of melanoma–threatening nevi, as well as other pigmented neoplasms of the skin, is a violation of the processes of division of melanocytes – skin cells containing melanin granules. Usually such cells are more or less evenly distributed in the skin and protect the body from exposure to ultraviolet rays. For a number of reasons, such as hereditary and genetic factors, the influence of certain chemical compounds, damage to the skin by mechanical means, ultraviolet light or radiation, there is a violation of the cell division of melanocytes. As a result of this violation, a cluster of pigment cells forms on a limited area of the skin, which looks outwardly like a brown or almost black spot of various sizes.
Some researchers believe that the appearance of melanoma-threatening nevi and other similar formations always has an innate nature and is caused by disturbances in the migration of melanocytes into the epidermis from the neuroectoderm. Proponents of this theory believe that any other factors, the role of which is seen in the development of moles, only provoke a further aggravation of this violation. Thus, the development cycle of melanoma–threatening nevi from this point of view looks like “a violation of embryogenesis – the development of the birthmark itself under the influence of various factors – malignancy and the appearance of melanoma.” In the light of this theory, melanoma is considered as a condition caused by congenital factors. Moles are found either immediately at the birth of a child, or after a few years or even decades – such a delay does not mean that there is no “innateness” of a melanoma-threatening nevus, it’s just that at first the skin defect is so small that it is invisible even with the most thorough examination.
Classification and symptoms
All moles or nevi are divided into two large varieties – melanoma-threatening and melanomone-threatening. Among the first, there are several main types that differ in external manifestations, age of appearance, predominant localization on the body and other characteristics. In addition, melanoma-threatening nevi differ in the degree of oncogenic risk. The most typical representatives of such skin neoplasms include the following:
- Dysplastic melanoma–threatening nevus is the most severe type of melanoma-threatening formation. Throughout a person’s life, 90% of cases degenerate into malignant melanoma. This type of moles often has a hereditary character, sometimes their multiple formation on the body is observed (50 or more neoplasias). Localization of dysplastic nevi has no characteristic features, they can occur in different parts of the body. The color of the moles varies from light brown to almost black, the size is from 2 to 10 millimeters. They are usually registered shortly after birth, in some cases their spontaneous appearance is observed during puberty. Melanoma-threatening nevi of this type are flat, usually with fuzzy edges, before the onset of malignancy, their consistency does not differ from healthy skin to the touch.
- Blue melanoma-threatening nevus (Yadasson–Tiche type) – usually occurs throughout a person’s life and is a single (2-5 moles may occur less often) skin neoplasm of no more than 10 millimeters in size. Its surface protrudes above the skin in the form of a hemisphere, the covers of the nevus have a characteristic “tense” appearance, the color varies from light blue to dark or almost black. A favorite localization is the scalp, palms, soles, buttocks, but it can also occur in other parts of the body. Malignancy of the blue melanoma-threatening nevus most often occurs against the background of traumatization of the mole, including with its incomplete removal by cosmetological methods.
- Borderline pigmented nevus – this melanoma-threatening type of mole in the vast majority (80%) of cases is a congenital condition, in the remaining 20% of patients, nevus appears in early childhood. The size of the formation usually increases with age, usually 8-15 millimeters, in some cases more. This type of melanoma-threatening nevus has a brown color, which changes its intensity from the center to the periphery of the neoplasm, sometimes with the formation of concentric rings. Degeneration into melanoma most often occurs under the influence of trauma or ultraviolet radiation.
- Giant pigmented nevus is the most noticeable type of such neoplasms. It has an exclusively innate character. This type of melanoma-threatening nevi increases as a person grows, often reaches 5-7 centimeters in diameter. There are cases when neoplasms of this type covered a significant part of the patient’s body and reached the size of 30-40 centimeters. At the same time, the mole protrudes above the surface of the skin and has a brown or black color, forming a pronounced cosmetic defect. Malignancy of giant pigmented nevus is registered in about 10% of patients.
- Nevus Ota is a melanoma–threatening neoplasm that develops exclusively on the face in the area of innervation of the branches of the trigeminal nerve (on the skin of the zygomatic or subglacial region). It is a congenital condition caused by disorders of migration and differentiation of melanocytes. Melanoma-threatening nevus Ota is characteristic of Asian peoples of the Mongoloid race, other nationalities do not have such formations. Over time, it can reach a diameter of several centimeters, degeneration into melanoma is rarely observed, mainly under the influence of ultraviolet radiation.
- Dubreuil’s limited precancerous melanosis is a condition of unknown etiology, which by some dermatologists refers to melanoma–threatening nevi, by others to precancerous dermatosis. Most often, the disease occurs in the elderly. At first, a pigment spot forms on the surface of the skin of the face and neck, less often than other parts of the body, which has uneven edges resembling the contours of geographical maps. The spot gradually increases in size, papules, nodules and other formations appear on its surface over time. Dubrey’s limited precancerous melanosis is an obligate precancerous condition, in the absence of treatment it almost always leads to the development of malignant melanoma.
In most cases, the determination of melanoma-threatening nevi is made by examining the neoplasm by a dermatologist. The doctor pays attention to the color, size, shape and nature of the contours of the mole (smooth or torn, fuzzy), by palpation determines its consistency and the presence of seals or other changes relative to healthy skin. When questioned, the specialist determines the age at which this nevus was first recorded, finds out whether there were any facts of its growth in the anamnesis, how fast the growth was, whether there were any other subjective symptoms (itching, burning, pain) at the location of the neoplasm. All this makes it possible to diagnose a melanoma-threatening nevus and pre-determine the signs of its malignancy.
A tissue biopsy with their subsequent study can provide more accurate data on the nature of the nevus. However, since a mechanical injury can trigger the development of a malignant process, oncologists and dermatologists avoid using this method to study melanoma-threatening nevi. Histological examination is possible only after the removal of the neoplasm surgically in compliance with all precautions. The structure of the tissues of melanoma–prone nevi is characterized by a large number of melanocytes of varying degrees of differentiation – the lower it is, the higher the probability of developing melanoma. In some cases, additional research methods are used to determine this condition – dermatoscopy, thermographic examination of the affected areas of the skin and a number of others.
The only reliable method of treating a melanoma-threatening nevus is surgical removal of a neoplasm with a wide excision of skin tissues. If the mole has a very large size (giant pigmented nevus), a skin transplant from a donor or from other parts of the patient’s body may be required. In many cases, skin plastic surgery is performed not only for preventive, but also for cosmetic purposes, especially with a significant size of the mole and its location on a noticeable part of the body. Removal of a melanoma-threatening nevus must be performed only with the participation of an oncologist – cosmetic removal techniques (cryodestruction, electrocoagulation, and others) may not only not rid the patient of this formation, but also cause his rebirth into melanoma.
Prognosis and prevention
The prognosis in the presence of melanoma-threatening nevi depends on a huge number of factors: the type of neoplasm, its location, working conditions and lifestyle of a person, and even the climate in which he lives (in southern areas, the skin is exposed to more intense UV rays, which increases the risk of developing melanoma). After surgical excision of the nevus, dispensary observation by an oncologist or dermatologist is necessary for timely detection of signs of malignancy. A similar approach is used for other moles with a relatively low oncogenic risk (for example, with blue nevus) – patients with non-removed neoplasms are examined by a specialist every 3-6 months.