John McCain, the Panama-born senior United States Senator from Arizona and former POW, was diagnosed with brain cancer following a surgery to remove a two-inch blood clot from above his left eye. McCain, who is 80, has battled cancer before, and his diagnosis has shocked and saddened his family and constituency.Cancer kills more than half a million Americans every year, and millions more battle cancer and survive. The Senator s battle against this deadly illness is a reminder of the fragility of human life, and of the importance of science, medical research, and healthcare coverage for the American people.Here s the statement released by his daughter on Twitter: Statement regarding my father @SenJohnMcCain: pic.twitter.com/SMte9Hkwkq  Meghan McCain (@MeghanMcCain) July 20, 2017Featured Photo by Chip Somodevilla/Getty Images