"The memory of Wendie Jo is that of a walking inspiration," Hanks said in a statement. "She met the challenges of her illness with love, cheer, joy and altruism. We are going to miss her as surely as we are all better for knowing her."
After being diagnosed with breast cancer in 1997, Sperber, a native of L.A., became an advocate for cancer care. In 2001, she founded the weSPARK Cancer Support Center, which provides free emotional support, information and social activities for individuals and families affected by cancer. She also helped unveil and promote a breast cancer stamp for the U.S. Postal Service in 1998.
"I get e-mails and letters from people saying weSPARK has changed their life," Sperber told PEOPLE in a 2002 interview. "And I know that's healing me."
The actress appeared in dozens of TV shows and movies, including all three Back to the Future films. She also had roles in Steven Spielberg's 1941, Robert Zemeckis's I Wanna Hold Your Hand, and Neal Israel's Moving Violations and Bachelor Party (also alongside Hanks). Her small-screen credits include Murphy Brown, Private Benjamin, Will & Grace and 8 Simple Rules.
On the Buddies set, "I remember her lifting me up when I felt bad," costar Telma Hopkins told PEOPLE in 2002. "Wendie had this great giggle. Tom and Peter (Scolari) would draw faces on their underwear and flash us while we were doing a scene, and she and I would bust up laughing."
Sperber is survived by a son and daughter, her parents, two sisters and a brother, the Associated Press reports.
For more information on weSPARK, go to www.wespark.org.