There is no single “first sign” of colorectal (bowel) cancer; symptoms vary and many overlap with benign conditions. Clinically, key warning signs include blood in stool (bright red or darker), a persistent change in bowel habits (constipation/diarrhea pattern shifts, narrower stools, going more or less often), and iron-deficiency anemia with unexplained fatigue. Abdominal cramps/pain, unintentional weight loss, and a feeling of incomplete emptying can also occur. The critical threshold is persistence—symptoms lasting beyond ~2–3 weeks or progressively worsening should not be ignored. Age, family history, and personal risk factors (prior polyps, inflammatory bowel disease) change screening and evaluation strategy. Bottom line: bleeding or sustained bowel change should trigger medical assessment; early detection significantly improves outcomes.