People from across Japan and around the world are sending messages of encouragement to Rikako Ikee.
One is from Rio de Janeiro Olympic gold medalist Sarah Sjostrom. Ikee practiced with the Swedish swimmer last October.
Japan's Sports Agency chief Daichi Suzuki is also an Olympic gold medalist in swimming. He said that when he first heard the news, he was stunned and at a loss for words. He said he hopes she will focus on her treatment and get well so we can see her swimming again.
Actor Ken Watanabe has been fighting leukemia for three decades. His message read: "Believe in today's medicine, believe in your own power to live, look forward, try not to be frustrated, and focus on your treatment. With heartfelt prayers."