The Duchess of York has been diagnosed with malignant melanoma, her spokesman has said.
The disease was discovered after several moles were removed when she was treated for breast cancer in June.
One of the moles was found to be cancerous and doctors are working to establish if it was caught early.
Here the Telegraph answers some common questions on the condition.
What is melanoma?
It is an aggressive and deadly form of skin cancer that occurs in cells in the skin called melanocytes.
It is one of the two main types of skin cancer, the other being non-melanoma, which is considered less aggressive and more treatable if caught early enough because it spreads less quickly.
What are the symptoms of melanoma?
Melanomas can appear anywhere on the body but are more common in areas that are often exposed to ultraviolet light from the sun.
Rarer types can also affect the eyes, soles of the feet, palms of the hands or genitals.
What puts someone at risk of developing this cancer?
The main cause of melanoma is ultraviolet light, from the sun and sunbeds.
Older people are more likely to develop it than younger people, and those with red or blonde hair, green or blue eyes, and pale skin, are all at increased risk.
Other factors include a family history of skin cancer, having lots of moles or freckles, prolonged exposure to the sun or sunbeds, and regularly being sunburnt.
The NHS encourages all people, and children in particular, to use sun protection and avoid the sun at the hottest part of the day. People with black or brown skin are less at risk.
How does melanoma get diagnosed?
The GP will take pictures of any areas of concern to be examined and if referred to a specialist, a dermatologist, a biopsy, or sample of the skin, will usually confirm a diagnosis.
Further tests may follow, including blood tests, and CT and MRI scans, to assess if and how far the cancer has spread. This will affect the treatment.
How is melanoma skin cancer treated?
Surgery is the most common form of treatment, with the aim of removing the melanoma, for example the affected mole, and an area of healthy skin around it, to help reduce the chance of it returning.
If it has spread to other areas, these will also need to be removed, which can include swollen lymph glands that make up part of the body’s immune system.
Radiotherapy may be used to reduce the size of the cancer, and targeted immunotherapy drugs, which help the body identify and attack the cancer cells itself, can be used in cases where it has spread and/or surgery is not an option or has not been effective.
Chemotherapy is less effective for skin cancer and usually reserved to treat advanced cancer that has spread to other parts of the body.
What are the chances of survival?
If it is caught and treated early enough – at stage 1 – when the cancer is only in the skin and has not spread, almost everyone survives beyond five years, according to Cancer Research UK.
This drops to 80 per cent for people diagnosed at stage 2, 70 per cent at stage 3, when it has spread to nearby areas like lymph nodes, and then 30 per cent at stage 4, where it is advanced and has spread to other parts of the body.
Overall, 85 per cent of melanoma patients are alive 10 years or more after diagnosis.