Towle's death was announced in a post on her social media channels Thursday.
"An endless ray of sunshine. A daughter, sister, friend to so many," the post read in part.
A message in the post's caption added, "We will always love you so much Sydney. I am so proud of how hard you fought. I love you."
Towle first began documenting her health journey on social media in 2023, sharing at the time that she had been diagnosed with a rare cancer called intrahepatic cholangiocarcinoma, where cancer cells grow in the liver's bile ducts, according to the National Cancer Institute.
The NCI notes that there are no routine screening tests for bile duct cancers prior to exhibiting signs and symptoms, which can include yellowing of the skin or jaundice, dark urine, clay colored stool, abdominal pain, fever, itchy skin, nausea, vomiting or unexplained weight loss.
Towle began sharing her experience undergoing cancer treatment across her social media accounts more frequently starting in 2024, posting regularly about her chemotherapy and surgery in the years that followed.
In May this year, she revealed her doctor had told her she was nearing the end of her treatment options.
"This week, my oncologist who I've been seeing for about 2 years walked into my hospital room and told me I'm at the end of my rope," Towle wrote in part in an Instagram caption. "I don't think there's a way to process that sort of statement when internally you feel so full of life."
More recently, Towle shared several videos of herself from a hospital bed, including one on July 22, in which she stitched a previous video of herself saying "It's a great day to have a great day."
Towle shared her final video on July 23, writing in the caption that she had been in the hospital for "exactly one month."
"It doesn't quite feel that long I think because I've been in and out of hospitals for a lot longer than that," she wrote, adding, "Everything feels like a dream in a lot of ways. I'm constantly asking myself what is real and what isn't, which is both a struggle and also sometimes really good."
The Cholangiocarcinoma Foundation, which Towle partnered with as a community champion, remembered her this week as an advocate who wanted to help others.
"Syd had a genuine sense of how sharing her life could help others, and she used that to promote understanding of how isolating a rare disease can be, of young adults facing cancer, of the importance of research funding, and of the value of living in the moment," the foundation said in a statement to ABC News. "She could have stayed isolated in her experience, but she invited the world in, so no one had to be alone in their struggles."
"We have been able to provide resources to and support so many because of Syd's advocacy," the organization added. "We will always honor her legacy by being even more committed to supporting patients and caregivers and finding a cure. Syd wouldn't want anyone to go this alone."
This is a developing story. Please check back for updates.