PENNSYLVANIA  —  A lot of people put on weight as they age, but a Pennsylvania woman’s weight gain was due to something much more serious.

According to NBC 10’s Randy Gyllenhaal, Mary Clancey lost 140 pounds in a matter of hours when doctors removed a massive tumor from her body.

“You can’t imagine in your wildest dreams something that huge,” she said.

The 71-year-old had been slowly gaining weight for 15 years, and first thought it was just old age, genetics, or maybe a bad diet. By last year, though, she weighed 350 pounds and had difficulty leaving the house.

“It got harder and harder to walk, when I laid on my back whatever was in there pressed against my lungs. I couldn’t get out of bed, and that’s when they took me to the hospital,” said Mary.

She went to Lehigh Valley Cedar Crest, where doctors did an MRI and found a 140-pound ovarian mass equal to 17 gallons of water.

“So this is predominantly liquid, 95% of it’s liquid,” said Dr. Richard Boulay of the Lehigh Valley Health Network.

Boulay had the tricky assignment of removing the tumor.

“And it’s slippery and nasty and if you pop one of these things it will have cancer cells inside it,” he said.

Mary will still be monitored for cancer, but now she can walk around again. She also warns that whatever grew inside her could happen to anybody gaining an unusual amount of weight.

“But it was a happy little cyst, it just kept growing and didn’t cause pain, and it just made itself comfortable in there. It probably would have killed me eventually, so I’m glad that I got to the hospital in time,” she said.

The giant mass more than doubled Mary’s body weight, being 365 pounds at her heaviest.