Arizona’s U.S. Senator John McCain has been called a fighter. The senior statesman learned last month that he is in for a very big fight—and it’s not just against fellow Republicans. On July 19, McCain’s office announced that the 80-year-old senator had a brain tumor, a glioblastoma, which is an aggressive type of cancer.

The next day, McCain tweeted, “I greatly appreciate the outpouring of support—unfortunately for my sparring partners in Congress, I’ll be back soon, so stand-by!”

True to his word, McCain returned to Washington, D.C., on July 25. After urging his colleagues to work toward a bipartisan overhaul of the Affordable Care Act (often called Obamacare), days later, in a surprise move, McCain voted with Republicans Susan Collins of Maine and Lisa Murkowski of Alaska to defeat the latest attempt to repeal the ACA.

McCain has faced his share of adversity. He was a prisoner of war in Vietnam for over five years after his plane was shot down. He has fought cancer before, too. McCain has had melanoma (skin cancer) and the cancers could possibly be related—a 2014 medical study found that gliomas occurred more often in people who had also had melanoma than in those who never had skin cancer.

McCain had surgery at the Mayo Clinic Hospital in Phoenix to remove a blood clot above his left eye on July 14. Days later, tests showed he had a glioblastoma. According to a statement from the senator’s office, scans show that all the tumor tissue was removed. But glioblastomas often reoccur or continue to grow from microscopic pieces. Treatment might include chemotherapy, radiation or a combination of the two.

In a letter released by Meghan McCain, she called her father “the toughest person I know.” She went on to say, “Cancer may afflict him in many ways: but it will not make him surrender. Nothing ever has.”