In her buoyant pop track “Dance You Outta My Head,” the musician Cat Janice sings about “dancing on the edge of disaster.” As her own health outlook darkened amid a grim fight with cancer, the song caught fire online, with thousands of supporters heeding her call to sway, and even groove, in the face of tragedy.

Born Catherine Janice Ipsan, the singer and multi-instrumentalist started writing music as a teenager and released it throughout her 20s. But “Dance You Outta My Head,” which she shared on social media alongside candid discussion of her grueling cancer treatments, quickly became the biggest hit of her career.

Ms. Ipsan released the song on Jan. 19, a few days after entering hospice care. TikTok users — including celebrities like Jason Derulo — began to leave messages of support. Some used the song to accompany their videos as a show of solidarity with Ms. Ipsan and her 7-year-old son, Loren, to whom she said she had transferred the song’s rights, positioning the song as a gift to her son in perpetuity.

“I changed all the rights from my songs so every presave and every stream goes to Loren,” Ms. Ipsan wrote on Instagram last month. The song has been used in more than two million TikTok videos and became the singer’s first song to enter the Billboard charts.

“I’m praying my story isn’t over yet,” she wrote in a post on her birthday, the day after the song’s release. “But if it is, this is a pretty incredible way to say goodbye.”

Ms. Ipsan died on Wednesday at her family home in Annandale, Va. She was 31.

The cause was sarcoma, according to William Ipsan, her brother.