The Duchess of York’s illness is once which can spread to other areas of the body, according the NHS England.
It’s main cause is ultraviolet light, which comes from the sun and is used in sunbeds.
The NHS website states: “Things that increase your chances of getting melanoma include your age and having pale skin, a large number of moles and a family history of skin cancer.
“It’s often possible to prevent skin cancer by being careful in the sun – for example, by using sunscreen and reapplying it regularly.
“How melanoma is treated depends on where it is, if it has spread to other areas of your body and your general health. Surgery is the main treatment.”
The Duchess was diagnosed with breast cancer last years.
The disease was discovered after several moles were removed during treatment for her last cancer.
One of the moles was found to be cancerous and doctors are working to establish if it was caught early.
The 64-year-old is said to be in “good spirits” despite the fact another cancer diagnosis so soon after the last one has been “distressing”.
Her spokesman said: “Following her diagnosis with an early form of breast cancer this summer, Sarah, Duchess of York has now been diagnosed with malignant melanoma.
“Her dermatologist asked that several moles were removed and analysed at the same time as the Duchess was undergoing reconstructive surgery following her mastectomy, and one of these has been identified as cancerous.
“She is undergoing further investigations to ensure that this has been caught in the early stages.
“Clearly, another diagnosis so soon after treatment for breast cancer has been distressing but the Duchess remains in good spirits.
