Non-melanoma skin cancer is a malignant tumour that starts in cells of the skin. Malignant means that it can spread, or metastasize, to other parts of the body.
The skin is the body’s largest organ. It covers your whole body and protects it from injury, infection and ultraviolet (UV) light from the sun. The skin helps control your body temperature and gets rid of waste materials through the sweat glands. It also makes vitamin D and stores water and fat.
The skin has 2 main layers. The top layer, on the surface of the body, is called the epidermis. The dermis is below the epidermis. It has nerves, blood vessels, sweat glands, oil (sebaceous) glands and hair follicles. The epidermis is made up of 3 types of cells:
Cells in the skin sometimes change and no longer grow or behave normally. These changes may lead to non-cancerous, or benign, tumours such as dermatofibromas, epidermal cysts or moles (also called nevi).
Changes to cells in the skin can also cause cancer. Different types of skin cells cause different types of skin cancers. When skin cancer starts in squamous cells or basal cells, it is called non-melanoma skin cancer. When cancer starts in melanocytes, it is called melanoma. Find out more about melanoma.
When skin cells change and become abnormal, they can cause precancerous conditions. This means that the cells are not yet cancer but there is a higher chance these abnormal changes will become non-melanoma skin cancer. The most common precancerous conditions of the skin are actinic keratosis and Bowen’s disease.
Sometimes changes to squamous cells or basal cells can lead to skin cancer. Most often, non-melanoma skin cancers start in basal cells. This type of cancer is called basal cell carcinoma (BCC) of the skin. It makes up about 75% of all non-melanoma skin cancers. Non-melanoma skin cancers can also start in squamous cells. This type of cancer is called squamous cell carcinoma (SCC) of the skin. It makes up about 20% of all non-melanoma skin cancers.
Rare types of non-melanoma skin cancers can also develop. These include Merkel cell carcinoma and Kaposi sarcoma.