Compound nevus

by Allison Osmond MD FRCPC and Archan Kakadekar MD
March 9, 2023

What is a compound nevus?

A compound nevus is a very common non-cancerous type of skin tumour made up of specialized cells called melanocytes. Compound 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 compound nevus a type of cancer?

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

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, because compound nevi are so common, the actual risk of a compound nevus turning into melanoma over time is very low.

What causes a compound nevus?

A compound 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 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.

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

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.

How do pathologists make the diagnosis of compound 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 compound nevus look like under the microscope?

When examined under the microscope, compound nevi are made up of large round melanocytes. The melanocytes are found in both the epidermis (the layer of tissue at the surface of the skin) 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.