3.1.1 Melanocytic Nevus

Mole, sometimes just called “nevus”.

Melanocytic naevi are very common (even ubiquitous, even in African populations) and may be present at birth. The number of melanocytic naevi increases with age until the age of around 30 years but there may be involution over time as well. A new melanocytic lesion appearing after the age of 30 years should raise clinical suspicion for malignant melanoma.

Acquired benign neoplasms of melanocytic lineage are termed melanocytic nevi (the plural of nevus). They are collections of melanocytes (naevus cells) in the epidermis, dermis or both.

Acquired melanocytic nevi express a high diversity of clinical appearance and histomorphology, age of onset mostly during first two decades of life, anatomic site, and genetic alterations. Melanocytes arise from the neural crest and migrate to the skin during embryogenesis. Most melanocytic naevi appear during the first two decades of life. Increased exposure to UV light in childhood seems to be a promoting factor, particularly episodes of sunburn. Melanocytic nevi tend to disappear with aging.

These skin-coloured or mostly pigmented macular, papular or nodular lesions are usually asymptomatic, but can occasionally be itchy or uncomfortable if irritated. They should be symmetrical, with a smooth outline, homogeneous, with a regular border, of small diameter (<6 mm) and stable over time. (see ABCDE rules/’ugly duck’ concept in the Melanoma chapter; for Atypical melanocytic nevus see chapter 9.7.).

Melanocytic nevi may occur anywhere on the body, sometimes on the oral and genital mucosa or in the sclera or retina of the eye.

Variants: junctional nevus, dermal nevus and combination of both compound nevus; blue nevus, combined nevus ( acquired plus blue nevus), Mongolian spot, congenital (hairy) nevus, halo naevus. Spindle- and epithelioid cell nevus.

No laboratory tests are needed.

Proliferation of melanocytes, single or in nests, epidermal (junctional nevus), dermal (dermal nevus), or at both levels (compound nevus). Melanocytic naevi with histological signs of atypia are referred to as dysplastic naevi (see separate chapter 9.7 Atypical melanocytic nevus).

Progression towards atypical melanocytic nevi possible, for melanoma is exceptional (except in cases of giant congenital nevus, see chapter 3.1.6 Congenital Melanocytic Nevus), but patients with more than 100 nevi are at higher risk of developing a melanoma. Multiple enlarged acquired nevi have increased melanoma risk.

The number of melanocytic naevi (>50), along with skin type and history (severe sunburns in childhood) are the most important risk factors for melanoma. Irritated or excoriated naevi are sometimes mistaken for cancer.

ABCDE rules/’ugly duck’/’mole out of context’ concept may help distinguish benign from malignant lesions. Clinical features, dermatoscopy (where images are magnified x10), histology. 

Other pigmented, usually acquired skin lesions including seborrheic keratosis, pigmented basal cell carcinoma; less often dermatofibroma, haemangioma. Different subtypes of early melanomas.

Abstention, excision if there is esthetic discomfort, irritated nevi by trauma or localization or in case of atypical nevi or suspicious melanoma.

Excision if there is an  irritated nevus by trauma or localization with constant irritation. Usually observation/ abstention (using the ABCDE rules to guide decision) if there is diagnostic doubt or functional problems. Digital images in the clinical record may be helpful to facilitate accurate long-term follow-up. Visible change in the digital record within three months of follow-up is an absolute indication for excision.