Meilin Keen was diagnosed with stomach cancer at 26. She’s part of a growing demographic of people who are getting cancer diagnoses before the age of 50. And doctors don’t know why. WSJ’s Brianna Abbott explains what we know so far. Further Reading: -Cancer Is Striking More Young People, and Doctors Are Alarmed and Baffled.  -Many Cancers Are on the Rise in the U.S., Even as Overall Deaths Fall.  -Uterine Cancer Was Easy to Treat. Now It’s Killing More Women Than Ever.  Learn more about your ad choices. Visit megaphone.fm/adchoices