After getting engaged, the only words journalist Mrinali Dhembla expected to hear were “I do.” Instead, she was told, “You have cancer.” “When I first heard the words, ‘You have cancer,’ I was obviously very shaken because when you’re in your 20s, you just think that a little disturbance in your bowels isn’t a big thing. You can just live through it,” said Dhembla, 27. Dhembla was diagnosed early last year with an aggressive Stage 3 rectal cancer that had already spread to her spine, part of a troubling rise in colorectal cancer among adults under 50. Treatment would typically…