Julia Louis-Dreyfus has breast cancer.
The Seinfeld and Veep star revealed the diagnosis on Twitter.
"One in eight women get breast cancer. Today, I'm the one," she wrote.
The Emmy Award-winning actress took the opportunity to call for universal healthcare in the US.
"The good news is that I have the most glorious group of supportive and caring family and friends, and fantastic insurance through my union.
"The bad news is that not all women are so lucky, so let's fight all cancers and make universal health care a reality."
The 56-year-old was a supporter of US President Barack Obama and failed contender Hillary Clinton. The current President, Donald Trump, is working to undo Mr Obama's healthcare reforms that expanded health insurance to millions who previously didn't have it.