On the episode, airing March 11, the 73-year-old actress appears with her husband, Tony Cacciotti, along with her "The Mary Tyler Moore Show" castmates Cloris Leachman and Ed Asner.
Harper reveals during the episode that Cacciotti initially hid the diagnosis from her after learning of it from her doctors because the prognosis was so short.
"I didn't get it because my husband hid it. Poor baby; he was so bereft," the actress says. " said there is nothing we can do for her and three to six months; maybe."
The CBS Television Distribution show will also have Harper's medical team from Cedars Sinai Medical Center in Los Angeles on the show to discuss her treatment. "The Doctors" co-host, Dr. Travis Stork, will also shed light on Harper's ailment.
Harper told People magazine that she has leptomeningeal carcinomatosis, which causes cancer cells to spread into the fluid-filled membrane around the brain.
Harper told the magazine that she is trying to maintain a positive outlook.
"I don't think of dying," she said. "I think of being here now."