The "Veep" star tweeted that she has been diagnosed with the disease and pleaded for universal health care to help others going through similar battles.
"1 in 8 women get breast cancer. Today, I'm the one," she wrote. "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."
This month she won her eighth individual Emmy Award, tying a record for actors set by Cloris Leachman. Louis-Dreyfus, 56, was diagnosed with cancer the day after the ceremony, a spokesperson from HBO confirmed.
"Veep" is entering its last season, and the HBO representative added that the production schedule will be adjusted if needed.
"Our love and support go out to Julia and her family at this time," HBO said in a statement. "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.'"
And former off-screen Vice President Joe Biden tweeted, "We Veeps stick together. Jill and I, and all of the Bidens, are with you, Julia."