Diane Lane, Marcia Cross and Mark Harmon are set to join more than 100 celebrities for Friday's "Stand Up To Cancer" telethon.
Kyra Sedgwick, Jay Leno and Ryan Seacrest also have been added to the list for the hourlong fundraiser, to be simulcast commercial-free by ABC, CBS, Fox, NBC and a number of cable channels.
Other previously announced stars include Sally Field, Kareem Abdul-Jabbar and George Clooney.
Donations to the telecast are intended to fund innovative cancer research. The first telethon, in 2008, helped raise more than $100 million.
"Stand Up to Cancer," hosted by news anchors Katie Couric, Diane Sawyer and Brian Williams, will air at 8 p.m. EDT Friday. It also will be seen on the Armed Forces Network.