Is a melanocytic (pigmented cell) naevus (mole) cancerous?

From the Guidelines

No, a melanocytic nevus (commonly called a mole) is not cancerous. It is a benign growth of melanocytes, which are the pigment-producing cells in the skin. These moles are extremely common, with most people having between 10-40 of them on their body. While melanocytic nevi are not cancerous themselves, they should be monitored for changes as some can potentially develop into melanoma, a dangerous form of skin cancer.

Key Points to Consider

• You should watch for changes in size, shape, color, or symmetry using the ABCDE rule: Asymmetry, Border irregularity, Color variation, Diameter larger than 6mm, and Evolution or change over time, as recommended by the US Preventive Services Task Force 1.
• Regular skin self-examinations and dermatologist check-ups are recommended, especially for those with numerous moles, atypical moles, or a family history of skin cancer.
• If you notice concerning changes in a mole, consult a dermatologist promptly for evaluation.
• The use of dermoscopy by an experienced physician can enhance diagnostic accuracy, and automated videodermoscopy systems can provide improved diagnostic accuracy for patients with multiple atypical naevi in the follow-up, as noted in the ESMO clinical practice guidelines for diagnosis, treatment, and follow-up of cutaneous melanoma 1.
• Machine-learning algorithms trained on either standard or dermatoscopic images have been shown to correctly diagnose pigmented skin lesions, with a success rate comparable to that of a panel of 21 board-certified dermatologists, although their use in clinical practice remains to be evaluated 1.

From the Research

Melanocytic Naevus and Cancer

• Melanocytic naevus is generally considered a benign skin condition, but it can be challenging to differentiate from cancerous lesions like melanoma 2.
• The classification of melanocytic lesions has traditionally been dichotomous, with lesions being classified as either benign (nevus) or malignant (melanoma) 3.
• However, recent studies have proposed the concept of "intermediate" melanocytic tumors, which have genetic progression events beyond those of melanocytic naevi but are not fully malignant 4, 5.
• These intermediate tumors, also referred to as melanocytomas, are thought to have an increased risk of malignant transformation compared to nevi 5.

Diagnosis and Classification

• Several methodologies have been proposed to diagnose melanoma and differentiate it from benign skin conditions, including the ABCD rule, Menzies method, and score-based methods like the 7-point checklist and CASH algorithm 2.
• Reflectance confocal microscopy (RCM), integrated clinical and dermoscopic risk scoring system (iDscore), and deep convoluted neural network (DCNN) are also used to aid in diagnosis 2.
• The classification of melanocytic naevi is based on clinical, histopathological, and genetic features, with specific subtypes of nevi having distinct genetic mutations 4, 5.

Relationship between Melanocytic Naevus and Melanoma

• Melanocytic naevi are thought to exist on a genetic spectrum that corresponds to biological behavior, with multiple pathways to melanoma development 4.
• The precise placement of tumors on these pathways and the corresponding risks of progression remain to be established 4.
• Melanocytomas are considered to be intermediate lesions with an increased risk of malignant transformation, but the exact risk is not yet quantified 5.