"Ronan" is dedicated to a 3-year-old boy who died last year of neuroblastoma. Swift wrote the song after reading the blog of Ronan's mother, Maya Thompson, who is credited as a co-writer.
According to a person familiar with the show, but who asked not to be identified because they were not authorized to speak, the song has never been performed in public. After the telethon, it will be available on iTunes; proceeds will go to cancer-related charities.
"Stand Up to Cancer" will air on all the major networks and cable channels. Besides Swift, it will feature celebrities including Tom Hanks, Julia Roberts, Gwyneth Paltrow, Justin Timberlake and more.