On the "Today" show, a clip of Harper's interview with Vieira shows the actress talking candidly about her battle with brain cancer. Harper's doctor said that she has "defied the odds." A one-on-one interview with Harper and Vieira will air Sept. 19 on NBC.
Despite her illness, TMZ reports that Harper is among the upcoming cast of the 17th season of ABC's "Dancing With the Stars." An official cast announcement will be made Sept. 4 on "Good Morning America."
Harper also recently filmed a TV movie in Canada entitled "The Town That Came A-Courtin'." The movie, also featuring Lauren Holly, Cameron Bancroft and Lucie Guest, will air in January 2014.
Harper, who starred as Rhoda Morgenstern on "The Mary Tyler Moore Show" and its subsequent spin-off "Rhoda," was told she may have "as little as three months left to live" in March 2013. Read more about her diagnosis here.
Harper's Broadway outings include Looped, The Tale of the Allergist's Wife, Ovid's Metamorphoses, Paul Sills' Story Theatre, Something Different, Subways Are for Sleeping, Wildcat and Take Me Along.
Watch the interview with Harper below: