Hi, just found out I have stage 3 rectal cancer

I'm 46, don't have any health issues, went in for routine colonospy and found out I have stage 3 rectal cancer with 4 suspected lymph nodes infected. My tumor is so low in rectum I'm being told that a colostomy is the most probable outcome. I will begin chemo and radiation before surgery. I'm scared, I've broken down a few times, Reading these posts has helped, thank you all for sharing. I have so many questions. But the one that concerns me most is, how often is does stage 3 diagnosis become a stage 4 at a later date after all treatments are completed