Mondale, 45, was diagnosed with the tumors in May, but chose to undergo oral chemotherapy and radiation, which could either kill the tumors completely or reduce them to a size that makes surgery safer.
She spoke to reporters from her Minnesota farmhouse about her treatment at the Mayo Clinic in Rochester, Minn.
"It's bad but not that bad," she said. "I've got a really good chance to beat it."
Mondale moved back to Minneapolis a few years ago after high-profile jobs in New York City and Los Angeles, including modeling for Vogue, acting in "Three's Company" and dating millionaire celebrities.
Her father said he has received supportive calls from former President Jimmy Carter and former Secretary of State Madeleine Albright. He told the Minneapolis Star Tribune he shares his only daughter's optimism.