Colorectal cancer rates are declining among older adults but rising dramatically in younger populations. People under 50 now see a 3% annual increase, while cases in those over 65 drop 2.5% per year. Most early-onset cases occur in the lower colon and rectum.
Doctors credit screening for the decline in older patients. Routine colonoscopies beginning at age 45 allow removal of precancerous polyps. But younger patients, often diagnosed later, face more aggressive, metastatic disease.
Researchers point to changes since the 1960s: rising obesity and sedentary lifestyles, increased antibiotic use in childhood, dietary shifts toward ultraprocessed foods and sugary drinks, and widespread microplastic exposure. These factors may disrupt the gut microbiome and promote chronic inflammation, a known cancer precursor. However, no single cause has been identified. The complex interaction between genetics, environment, and timing of exposure remains under investigation.
Symptoms include rectal bleeding, unexplained weight loss, anemia, abdominal pain, and changes in bowel habits. These often mimic benign conditions, delaying diagnosis. Experts urge patients under 45 with persistent symptoms to advocate for early screening, even if guidelines recommend starting at 45 for average-risk individuals.