Early-stage colon cancer may cause no noticeable discomfort; the most common first clue is a persistent change in bowel habits—diarrhea, constipation, or alternating patterns lasting more than two weeks. Stools become narrower, pencil-shaped, or are coated with mucus or blood, which may appear dark red or bright red. As the tumor grows, vague lower-abdominal cramping or bloating worsens after meals; if the lumen narrows, colicky pain and progressive distension develop. Systemic features include unexplained weight loss, fatigue, pallor from chronic blood loss, and low-grade fever. A hard, fixed mass may be palpable in the right or left lower quadrant. Perforation or complete obstruction presents with sudden severe abdominal pain, vomiting, and absence of stool or flatus, requiring emergency care. Late disease can manifest hepatomegaly, jaundice, ascites, or supraclavicular lymph-node enlargement. Any adult over 40 with altered bowel habits, blood in stool, or unexplained anemia should undergo prompt colonoscopy for diagnosis.
| Symptom Category | Key Features |
|---|---|
| Early warning | No discomfort; persistent change in bowel habit (>2 weeks): diarrhea, constipation, or alternating pattern |
| Stool appearance | Narrow, pencil-shaped; mucus or blood coating (dark red or bright red) |
| Abdominal signs | Vague lower-abdominal cramping / bloating, worse after meals; colicky pain & distension if lumen narrows |
| Systemic features | Unexplained weight loss, fatigue, pallor (chronic blood loss), low-grade fever |
| Palpable mass | Hard, fixed lump in right or left lower quadrant |
| Acute complications | Perforation / obstruction: sudden severe pain, vomiting, absence of stool or flatus → emergency |
| Late metastases | Hepatomegaly, jaundice, ascites, supraclavicular lymph-node enlargement |
| Action for high-risk | Any adult ≥40 years with altered bowel habits, blood in stool, or unexplained anemia → prompt colonoscopy |