Alex Trebek, noting the "curves and unexpected events" of pancreatic cancer treatment, announced Tuesday that he's undergoing additional chemotherapy.

The beloved Jeopardy! host shared a video update in which he called previous assessments of his treatment needs "premature" and said doctors are currently re-examining the situation.

"This summer, because I was making such good progress, we thought I was finished with chemo," he said. "That was a bit premature and certainly overoptimistic. I began immunotherapy, but that didn't go very well at all. My numbers went south dramatically and quickly . . . It appears that I will be having more chemo treatments ahead of me."

Trebek added that he and his doctors are "expecting good results again" and thanked fans for their continued support. "Believe me, it means a lot," he said.

Trebek also discussed this update with the Good Morning America team on Tuesday's show:

Elaborating on his transition from chemo to immunotherapy in the GMA interview, Trebek said the effects of this chemo treatment can very greatly. 

"For some reason, and I don't understand why, occasionally it will cause excruciating pain in my lower back," he said. "Other times it's fatigue, other times it's nausea. It varies. Cancer is mysterious in more ways than one."

As for his decades-strong Jeopardy! legacy, Trebek said he plans to continue on as host, adding that he'll be happy "as long as I can walk out and greet the audience and the contestants and run the game."