Why Do Some Moles Turn Cancerous While Others Do Not?

by Eileen Bailey Health Writer

Scientists understand what makes moles form but have long questioned why they stop growing and why some moles become cancerous while the majority do not. A recent study sheds some light on this question. Scientists at Perelman School of Medicine at the University of Pennsylvania have identified a genetic factor that keeps moles in a noncancerous form.

What causes moles to form?

Your skin contains cells called melanocytes. These cells contain melanin, which produce the color, or pigment, in your skin. Usually, the melanocytes are evenly spread out, however, when they grow in a cluster, a freckle, spot or mole develops. They can be light or dark, flat or raised, smooth or rough. Most people develop moles before the age of 20. Moles can remain throughout your life or disappear with time. Certain times of your life - pregnancy, teen years and over the age of 50 - are the most common times for moles to change.

Moles are formed because of a certain gene mutation, the BRAF gene. In a common mutation, this gene is stuck in the “on” position and causes the cells to grow in clusters. Once the mole is formed, the cells stop multiplying in this way.

Why don’t all moles develop into melanoma?

The question scientists faced is: why do the cells grow in clusters to form a mole and then stop once the mole reaches a certain size, usually a few millimeters in diameter? What stops the cells from continuing to grow and develop into melanoma in most moles?

Researchers at the University of Pennsylvania think they have come up with the answer, or at least a better understanding of why some moles remain benign and others develop into melanoma. The scientists discovered that a protein, called p15, was present in much higher quantities in benign moles. When they looked at moles which had developed into melanoma, the p15 protein was extremely low or undetectable. The research team inserted p15 into normal cells and cell growth completely stopped.

What does it all mean?

Right now, it is still too early to say whether or not this discovery will have any impact on the way we fight melanoma. The researchers hope that this knowledge can lead to more targeted treatments for melanoma. Dr. Todd Ridky, the lead author of the study, plans to further the research, looking for more understanding in how melanoma develops, how understanding p15 can help fight melanoma and what role the protein might play in other forms of cancer.

For more information on moles:

Moles, and Other Common Precancerous Skin Lesions

Atypical Mole Removal: A Dermatologist Answers Your Questions

Are your moles and freckles precancerous?

I have a Strange Looking Mole-Is it Skin Cancer?

What it is like to have a Mole Removed


“Atypical Moles,” Date Unknown, Staff writer, American Osteopathic College of Dermatology

“Moles,” Reviewed 2014, Oct. 10, Staff Writer, National Health Services (NHS-UK)

Eileen Bailey
Meet Our Writer
Eileen Bailey

Eileen Bailey is an award-winning author of six books on health and parenting topics and freelance writer specializing in health topics including ADHD, Anxiety, Sexual Health, Skin Care, Psoriasis and Skin Cancer. Her wish is to provide readers with relevant and practical information on health conditions to help them make informed decisions regarding their health care.