Sarah Ferguson, Duchess of York, said she has malignant melanoma, a form of skin cancer.
The diagnosis came after Ferguson had reconstructive surgery to treat breast cancer.
Writing in an Instagram post, the duchess said the news has been a shock.
Representatives for the Duchess of York told The Guardian on Sunday that the cancer was discovered while Ferguson was undergoing reconstructive surgery following a breast cancer diagnosis in June 2023.
"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," the spokesperson said in part of the statement.
Writing on Instagram, Ferguson said the new diagnosis had been a "shock" but that she has remained in "good spirits."
"I have been taking some time to myself as I have been diagnosed with malignant melanoma, a form of skin cancer, my second cancer diagnosis within a year after I was diagnosed with breast cancer this summer and underwent a mastectomy and reconstructive surgery," Ferguson wrote alongside a photo of herself.
Ferguson wrote that it was due to the "great vigilance of my dermatologist" that the melanoma was discovered.
"Naturally another cancer diagnosis has been a shock but I'm in good spirits and grateful for the many messages of love and support," she wrote.
Malignant melanoma can be caused by sun exposure
Malignant melanoma is a form of skin cancer that occurs when melanocytes, the cells that produce the melanin that gives skin its color, grow out of control. This can be caused by damage from the sun's UV radiation, but not always.
It's less common than other types, only accounting for around 1% of skin cancers, according to the American Cancer Society, but it causes a large majority of deaths from skin cancer in the US.
The symptoms of malignant melanoma include a new mole on the skin; a spot that changes in size, shape, or color; or a spot that looks different from all the other spots on your skin, according to the ACS.
How malignant melanoma is treated depends on the stage of the disease. Treatments commonly include the surgical removal of the melanoma for early-stage cancers and immunotherapy and radiation for later stages.
99% of people diagnosed with malignant melanoma will survive five years past diagnosis if the melanoma is detected early, but this drops to 35% if the cancer spreads to other organs.
Ferguson said: "I believe my experience underlines the importance of checking the size, shape, color and texture and emergence of new moles that can be a sign of melanoma and urge anyone who is reading this to be diligent."
Ferguson's statement comes less than a month after announcing in an Instagram post that she had fully recovered from breast cancer.
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