Junctional nevus

by Allison Osmond MD FRCPC and Archan Kakadekar MD
October 25, 2022

What is a junctional nevus?

A junctional nevus is a very common non-cancerous type of skin tumour made up of specialized cells called melanocytes. Junctional nevi (nevi is the plural of nevus) are more common in people with light-coloured skin and can be found anywhere on the body. Another name for this type of tumour is a mole. Mole is a common term used to describe any kind of growth made up of melanocytes.

Is a junctional nevus a type of cancer?

No. A junctional nevus is a non-cancerous growth.

Can a junctional nevus turn into melanoma over time?

About one-third of all melanomas (a type of skin cancer made up of melanocytes) are believed to arise from previously non-cancerous melanocytic nevi. However, because junctional nevi are so common, the actual risk of a junctional nevus turning into melanoma over time is very low.

What causes a junctional nevus?

A junctional nevus is caused by a combination of prolonged exposure to UV light (typically the sun) and genetic susceptibility.

What is the difference between a congenital nevus and an acquired nevus?

A junctional nevus that develops shortly after birth is called a congenital nevus. A junctional nevus that develops later in life (as a child or an adult) is called an acquired nevus.

What does a junctional nevus look like when examined without a microscope?

Most junctional nevi are flat and round to oval in shape. The border between the nevus and the surrounding normal skin is usually well-defined and easy to see. Without a microscope, these tumours can look pink, brown, black, or blue with most only showing a single colour.

How do pathologists make the diagnosis of junctional nevus?

This diagnosis can only be made after a tissue sample is examined under the microscope by a pathologist. This usually involves removing the entire nevus in one piece along with a small amount of surrounding normal-appearing skin.

What does a junctional nevus look like under the microscope?

When examined under the microscope, junctional nevi are made up of large round melanocytes. The melanocytes in a junctional nevus are found in a thin layer of tissue at the surface of the skin called the epidermis. Within the epidermis, the melanocytes are found either in small groups called nests or spread out as single cells near the bottom of the epidermis. Over time, the melanocytes in a junctional nevus will spread down towards another layer of tissue called the dermis. When the melanocytes are found in both the epidermis and the dermis, the growth is called a compound nevus. When the melanocytes are found only in the dermis, the growth is called a dermal (or intradermal) nevus.