The 84-year-old Hollywood legend made the announcement Friday, saying she's already started chemo treatments, and that she feels very lucky, as it's treatable and about 80% of people diagnosed survive.

In true and incredible Jane fashion, she also took a moment to bring awareness on the importance of health care and as an advocate for it to be affordable to everyone, saying, "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."

Jane says she'll be doing chemo for 6 months, and is handling the treatments quite well ... letting everyone know she won't let the diagnosis interfere with her climate activism.

She says, "We also need to be talking much more not just about cures but about causes so we can eliminate them. For example, people need to know that fossil fuels cause cancer. So do pesticides, many of which are fossil fuel-based, like mine."

Continuing, "We’re living through the most consequential time in human history because what we do or don’t do right now will determine what kind of future there will be and I will not allow cancer to keep me from doing all I can, using every tool in my toolbox and that very much includes continuing to build this Fire Drill Fridays community and finding new ways to use our collective strength to make change."

She finishes with a call to action, "The midterms are looming, and they are beyond consequential so you can count on me to be right there together with you as we grow our army of climate champions."