Kassidy Pierson, Who Went Viral Documenting Her Battle with Metastatic Melanoma, Has Died of The Disease

"I know I'm not the face you want to see," she wrote. "I am [Pierson's] older sister. And so I'm coming on here to let you guys know that she did pass away on Tuesday night."

She continued, "I wanted to also come on and thank you all so much for following and supporting, and I can't tell you the amount of times that she would just break down crying because she couldn't believe how many people just loved her from this platform. So just thank you so much, for all that you have done for her."

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Pierson later told Buzzfeed that she didn't have any additional treatments after her mole was removed. But a scan performed a year later found that the cancer had metastasized throughout her body, including to her brain. She underwent six years of treatments and surgeries to help manage her cancer.

"I've done many different kinds of treatments, including immunotherapy, chemo, targeted therapies, studies that were available at the time, clinical trials, radiation and multiple surgeries," Pierson said.

One in five Americans will develop skin cancer by age 70, according to the Skin Cancer Foundation, and more than two people in the US die of skin cancer every hour. When detected early, the five-year survival rate for melanoma, the least common but most serious form of skin cancer, is 99%, the foundation says, making regular skin cancer checks crucial.

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Pierson told Buzzfeed that she talked openly with her son about her impending death and that she's tried to leave mementos for him in the future. "I am writing letters, making videos and getting gifts for my child to prepare for the moments I won't be around for him," she said. "I want him to know how much he means to me. I know they won't replace who I am or me being in his life. But it will help him know who I am and give him a reminder on those special moments that his mommy is always with him."

Pierson also said that her days were full. "I've been staying busy visiting with as many friends and family as possible," she shared. "My days are booked full, as we don't know how long it'll take me to die. It could be a couple days, weeks, months, or even years. It just depends on the cancer and how fast or slow it moves throughout my body. But I feel good now, and so spending as much time with the ones I love is what I've been doing with my days."

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