JACKSONVILLE, Fla. -

Russ Dunn came to Florida to enjoy retirement, but now he's fighting cancer.

The 67-year-old was diagnosed after he received a liver transplant at the Mayo Clinic in Jacksonville.

Doctors say the new liver caused his cancer, and according to at least one independent expert and other medical sources, this probably could not have been prevented.

"It's a hard, hard existence knowing we all have a finite end, but mine's coming up pretty rapidly," said Dunn, who undergoes chemotherapy regularly.

He said it's how he developed cancer that is most frustrating. Two years ago, Dunn had a liver transplant at Mayo Clinic.

"I thought I'd live to see my grandkids. I was thrilled," Dunn said. "It was a hard operation. It was very difficult, but I was thrilled because I had a new lease on life. I was as optimistic as can be, and when I heard I had cancer, I was devastated. Absolutely devastated."

Ten months after the transplant, doctors diagnosed Dunn with cancer.

The paperwork from Mayo Clinic shows the transplanted liver is the source of the cancer.

Mayo Clinic issued this statement:

"To ensure the high quality of donated organs, Mayo Clinic works closely with outside organ procurement agencies to assess and evaluate donor organs. In our region, the organ procurement organization is LifeQuest located in Gainesville, Fla. Mayo Clinic's highest priority is ensuring that each patient receives the most effective, compassionate and safest care. Organ procurement organizations carefully screen donated organs and actively try to prevent disease transmission whenever possible. The risk of such transmission can never be zero."

A spokesperson for LifeQuest said all of its organs are run through a series of tests and that information is then shared with the transplant hospital.

LifeQuest said transmitting a disease through organ donation is not common, but happens.

Charlie Alexander, the CEO of the Living Legacy Foundation of Maryland, one of the other 58 organ procurement organizations in the United States but unrelated to this transplant, confirmed what LifeQuest said is true.

"Unfortunately, it is absolutely impossible to screen for every possible risk associated with receiving a transplant," Alexander said.

Dunn wants a new liver, but doctors are telling him he's not a candidate. So for now he'll keep fighting his cancer.

"I'm a dead man walking," he said.

Alexander said Mayo Clinic doctors are doing the right thing treating the cancer instead of performing another liver transplant.

As of now, Dunn is not planning litigation against Mayo Clinic.