Jeopardy host Alex Trebek says he has had a setback and is undergoing chemotherapy again for pancreatic cancer.

The Canadian-born game-show host said that after a short period of optimism when he stopped chemotherapy and began immunotherapy, his "numbers shot up," he told ABC's Good Morning America on Tuesday

"I was doing so well. And my numbers went down to the equivalent of a normal human being who does not have pancreatic cancer, so we were all very optimistic. And they said, 'Good, we're gonna stop chemo. We'll start you on immunotherapy,'" he said.

"I lost about 12 pounds in a week and my numbers went sky high, much higher than they were when I was first diagnosed. So, the doctors have decided that I have to undergo chemo again and that's what I'm doing."

Doctors regularly monitor a cancer patient's blood cell counts to determine how his or her body is handling the particular treatment.

Trebek said his goals for the summer were to get his strength and hair back, and his progress on both fronts was "dismal."

The 79-year-old announced in March he had Stage 4 pancreatic cancer. He received an outpouring of support from fans, including from Canadians.

Despite the diagnosis, he hasn't missed a day on the show, which tapes its episodes in advance.

Alex Trebek is seen with a birthday cake presented to him in July during filming of the 36th season of Jeopardy. (Jeopardy/Twitter)

In late August, in a video teasing the forthcoming Jeopardy season, the show released a video in which the Sudbury, Ont.-born host declared: "I'm on the mend and that's all I can hope for right now."