The 84-year-old Fonda said she's confident of overcoming this health crisis.
"So, my dear friends, I have something personal I want to share. I’ve been diagnosed with non-Hodgkin’s Lymphoma and have started chemo treatments," she posted to Instagram.
"This is a very treatable cancer. 80% of people survive, so I feel very lucky."
Dr. William Dahut, chief scientific officer for the American Cancer Society, agreed that Fonda has a fighting chance — depending on a host of factors.
"It is potentially a curable malignancy, depending significantly upon the sub-type of non-Hodgkin lymphoma and the degree of spread at the time of diagnosis," the oncologist told NBC News.
"For her, being optimistic is certainly within the realm of possibility and could very well be realized."
The acclaimed actor also said she has the better chance of survival based largely on the privilege of having “health insurance and access to the best doctors and treatments.”
“Almost every family in America has had to deal with cancer at one time or another and far too many don’t have access to the quality health care I am receiving and this is not right,” she added.
Dr. Dahut said he was moved by Fonda's statement that she's luckier than most Americans.
"Your survival is better with a Stage 2 tumor than you are with Stage 1 tumor if you're underinsured," he told NBC News.
"I thought that was very powerful statement. Cancer is such a terrifying experience and to acknowledge one's own privilege and ability to get the best therapies is very powerful."
Fonda, who won Best Actress awards for her "Klute" and "Coming Home" performances, told supporters that this diagnosis will not slow her down.
"I will not let any of this interfere with my climate activism," she said.
While Fonda has been a long-time activist for a host of liberal causes, in recent years she has focused her efforts on climate change.
She's been a regular at protests on Capitol Hill, donning a red coat and calling for more attention to the world's climate crisis.
Cancer and the climate crisis are linked, said Fonda.
"We also need to be talking much more not just about cures but about causes so we can eliminate them," she added. "For example, people need to know that fossil fuels cause cancer."