Compound nevus

by Allison Osmond MD FRCPC and Archan Kakadekar MD
November 14, 2024

A compound nevus is a very common non-cancerous type of skin tumour made up of cells called melanocytes. This type of growth is more common in people with light-coloured skin but can be found anywhere on the body. Another name for a compound nevus is a mole, which is a common term used to describe any growth of melanocytes.

Can a compound 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, compound nevi are very common, and the risk of a compound nevus turning into melanoma over time is very low.

What does a compound nevus look like?

Most compound nevi are slightly raised 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 growths can look pink, brown, black, or blue, with most only showing a single colour.

What causes a compound nevus?

A compound nevus is caused by prolonged exposure to UV light (typically the sun) and genetic susceptibility.

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

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

How is this diagnosis made?

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

Microscopic features

When examined under the microscope, compound nevi are made up of large round melanocytes. The melanocytes are found in the epidermis (the layer of tissue at the skin’s surface) and the dermis (a thin layer of tissue just below the epidermis). The melanocytes form groups called nests, although single cells may also be seen.

Most compound nevi develop from a very similar growth called a junctional nevus. In a junctional nevus, the melanocytes are only found in the epidermis. Over time, the melanocytes in a junctional nevus spread down towards the dermis, forming a compound nevus. When the melanocytes are found only in the dermis, the growth is called a dermal (or intradermal) nevus.