Despite the tough news, we're happy to hear that it sounds like she's in great hands.
"The good news is that I have the most glorious group of supportive and caring family and friends, and fantastic insurance through my union," Louis-Dreyfus wrote. "The bad news is that not all women are so lucky, so let's fight all cancers and make universal health care a reality."
Breast cancer is the second leading cause of cancer death in women. More than 250,000 new cases will be diagnosed in women in 2017, according to the American Cancer Society.
Fans were quick to show their support on social media.
"Stay strong and keep fighting," one wrote. "We love you."
HBO, which recently announced "Veep" is ending, sent the following statement to The Hollywood Reporter:
"Julia received her diagnosis the day after the Emmys. It had no bearing in the decision to renew 'Veep' for a final season. The writers will continue prepping as business as usual, and HBO will adjust the production schedule as needed."
"Our love and support go out to Julia and her family at this time," the statement continued. "We have every confidence she will get through this with her usual tenacity and undaunted spirit, and look forward to her return to health and to HBO for the final season of 'Veep.'"