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Can birthmarks turn into cancer?

This page is about birthmarks and cancer. There is information about


What birthmarks are

Birthmarks are coloured marks on the skin and there are many different types. The medical word for a birthmark is congenital naevus (pronounced nee-vus) or naevi (pronounced neev-eye) if there is more than one.

Birthmarks can start in the outside layer of the skin (epithelial naevi) or in the deeper layers (dermal or subcutaneous naevi). Different types of birthmarks are made up of different types of cells. For example, melanocytic naevi, are made of cells called melanocytes.


Birthmarks and skin cancer

Most birthmarks, such as the common port wine stains and strawberry marks, carry no risk of developing into a cancer. But a very rare type of birthmark, called a congenital giant melanocytic naevus, can develop into a melanoma. Melanoma is the most serious type of skin cancer.

Congenital birthmarks are brown or black moles that are present at birth or develop within the first few months. They are put into groups according to their size

  • Small – less than 1.5cm
  • Medium – bigger than 1.5cm but less than 20cm
  • Large – bigger than 20cm

The risk of small or medium sized congenital birthmarks developing into melanoma is similar to the average risk of developing a melanoma. There is a greater risk of a larger congenital birthmark – a giant congenital melanocytic naevus – becoming melanoma. They are very common on the buttock and are sometimes called bathing trunk naevi.

About half (50%) of the melanomas that develop in large congenital birthmarks do so by the age of 3 to 5 years. Doctors recommend that you check small or medium birthmarks regularly. But they recommend that if possible large congenital birthmarks are completely removed at an early age. Often this is not possible and the birthmark should be checked regularly for any signs of change. UK guidelines recommend that people who have large congenital melanocytic naevi should have their skin checked every year by a skin specialist (dermatologist). 

Other types of birthmarks that can develop into a skin cancer are those in the epidermis (upper layer of skin). These are called epidermal naevi. Some of these increase your risk of developing a type of skin cancer called basal cell carcinoma (BCC). These are not as serious as melanoma. They are usually easily removable with surgery. For most people, this will be all the treatment you need.

There is information about melanoma and non melanoma skin cancer, including basal cell carcinoma on this website.

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Updated: 16 September 2014