Transcript for Valarie Harper on 'Dancing With the Stars'
And now we move onto a kind of gladiator of hope and living life today. Valerie harper, earlier this year the actress revealed she had been diagnosed with terminal cancer and today she surprised fans, staring down her disease, joining the cast of abc's "dancing with the stars" and explaining when life asks you to dance, you just have to dance. Here's abc's linsey davis. It's a privilege and an honor to welcome valerie harper to our season 17 cast. Reporter: In january, doctors told her she had three to six months to live. Now, 9 months later, valerie harper is about to debut on "dancing with the stars." Reporter: She is the tv legend many know from her "mary tyler moore" days simply as -- rhoda! Reporter: Despite being diagnosed with terminal brain cancer, the 74-year-old says she is not about to sit on the couch and wait for death. I have a chance to do what i did 40 years ago, dance. Reporter: Her response to people who ask why -- more than anything, it's why not? I have this formal death sentence which is being extended out. And as long as I'm feeling well, I might as well dance. And if anybody gets even the slightest inspiration or utz or push toward life while we're living, mission accomplished. Reporter: Another mission of hers? To beat the cancer. Each two-month increment, the brain scan has looked better. And while doctors say the potential for bone weakness and exhaustion are possible concerns, they say many cancer patients get a tremendous psychological boost from physical activity. I'm looking for some old broads! Reporter: And now, the feisty sidekick who's kept us laughing for decades is teaching us all a lesson about living life to the fullest. If you're worried about dying, you can't be in the moment living. So that's my message to everybody. And in that moment, you might dance! Linsey davis, abc news, new york.
This transcript has been automatically generated and may not be 100% accurate.