Collection of Information to Better Understand Young Onset Colorectal Cancer

This study collects medical data and stool samples from young adults diagnosed with colorectal cancer (under age 50) to understand why rates of early-onset colorectal cancer are rising. It also collects data from older patients (50+) for comparison. The goal is to identify unique risk factors in younger patients. **You may be eligible if...** - You are 18–49 years old with a confirmed diagnosis of a gastrointestinal cancer (for the young-onset cohort) - You are 50 or older with a confirmed colorectal adenocarcinoma diagnosis with no prior treatment (for the comparison cohort) - You have no known hereditary colorectal cancer syndrome or inflammatory bowel disease (for stool collection) **You may NOT be eligible if...** - You have already received treatment (surgery, chemotherapy, radiation, immunotherapy) for colorectal cancer (stool cohort only) - You have a prior history of gastrointestinal cancer Talk to your doctor to see if this trial is right for you.