A mole (nevus) is a common skin growth that develops when pigment-producing cells called melanocytes grow in clusters. Most people have multiple nevi, which are typically harmless and remain stable for decades. However, the concern about a long-standing mole changing into melanoma, the most serious form of skin cancer, is well-founded. While the vast majority of moles never become malignant, a small percentage can transform, making vigilance necessary.
The Potential for Transformation
The transformation of a stable, benign mole into malignant melanoma is a rare event rooted in cellular genetics. A common mole often forms due to an initial genetic change, such as an activating mutation in the BRAF gene, causing melanocytes to proliferate into a cluster. These cells typically enter a state of permanent growth arrest, known as senescence, which prevents them from developing further.
This stable state can be overcome if the cells acquire additional genetic mutations over time, particularly the inactivation of tumor suppressor genes like CDKN2A or PTEN. Accumulated damage, often from chronic ultraviolet (UV) radiation exposure, drives this accumulation of mutations. When these secondary genetic events occur, the senescent brake is released, allowing the once-stable nevus cells to begin uncontrolled growth and progress toward melanoma. Approximately 25 to 33 percent of cutaneous melanomas are estimated to arise from a pre-existing mole.
Identifying Concerning Changes
Monitoring existing moles for shifts in appearance is a practical way to detect potential malignancy at its earliest and most treatable stage. Dermatologists recommend using the ABCDE method as a structured guide for self-examination. A stands for Asymmetry, meaning that if you draw a line through the mole, the two halves would not match.
B represents Border irregularity; benign moles typically have smooth, well-defined edges, while concerning lesions may show notched, scalloped, or blurred borders. C is for Color variation, referring to a mole having multiple shades (tan, brown, black, red, white, or blue) within the same lesion, rather than a uniform color.
D stands for Diameter, as melanomas are often larger than six millimeters (roughly the size of a pencil eraser). E is for Evolving, the most important criterion, referring to any change in a mole’s size, shape, color, or elevation over weeks or months. Any mole that begins to itch, bleed, or feel tender without injury should also be considered a sign of evolution.
High-Risk Moles and Monitoring Frequency
Certain types of moles carry a higher probability of malignant transformation and require closer attention. Atypical or dysplastic nevi often appear larger than common moles with irregular shapes and mixed colors, similar to early melanoma. Individuals with five or more dysplastic nevi face a risk of developing melanoma about ten times greater than the general population.
Large congenital nevi, moles present at birth, also have an increased lifetime risk of becoming cancerous, with the risk correlating to the size of the lesion. People who have a high number of common moles (more than 50) are also considered an increased risk group. A monthly self-examination using the ABCDE method is advisable for all individuals to track changes. Those with high-risk features, such as numerous or dysplastic moles, should plan for an annual professional full-body skin examination by a dermatologist.
Seeking Professional Evaluation
If a mole meets two or more of the ABC criteria, or if the Evolving criterion is noted, professional evaluation is necessary. Urgent symptoms include a mole that begins to bleed spontaneously, develops a persistent sore, or causes itching or pain. The appearance of any new, unusually dark or fast-growing spot after the age of 30 should also raise suspicion.
During the consultation, a dermatologist will examine the mole using a handheld magnification tool called a dermatoscope to view pigmentation patterns beneath the skin. If the lesion is suspicious, the definitive step is a skin biopsy, where the mole or a part of it is removed and sent for microscopic analysis. Early detection significantly increases the likelihood of successful treatment, which typically involves surgical excision of the cancerous tissue.