Signs and Symptoms of Colon Cancer
Colon cancer most commonly presents with rectal bleeding (hematochezia), iron deficiency anemia, and unexplained weight loss—these three "alarm symptoms" are the strongest predictors of colorectal malignancy and mandate immediate colonoscopy. 1, 2
High-Risk Alarm Symptoms (Require Immediate Colonoscopy)
Primary Red Flag Symptoms
- Rectal bleeding (hematochezia): Present in 46-58% of colorectal cancer cases, with a hazard ratio of 10.66 for colorectal cancer 1, 2, 3
- Iron deficiency anemia (ferritin <15 ng/dL): Occurs in 13-57% of cases, with a hazard ratio of 10.81 for colorectal cancer 1, 2
- Unexplained weight loss ≥5 kg (>11 pounds) within 5 years: Associated with 2.23 times higher odds of colorectal cancer, present in 10% of cases 1, 2
Additional Alarm Features
- Dark red rectal bleeding and palpable abdominal mass: Both have >95% specificity for colorectal cancer 1
- Bloody stool: Fresh blood in or on feces, particularly associated with lower intestinal bleeding 1
Common But Less Specific Symptoms
Gastrointestinal Symptoms
- Change in bowel habits: Present in 38.8-51% of cases, though less specific than bleeding 1, 3, 4
- Abdominal pain or discomfort: Occurs in 39.3-52% of cases, but has limited specificity 1, 3, 4
- Constipation: More predictive of distal colon cancers (odds ratio 3.16) 3
- Diarrhea: Can occur but is non-specific 1, 5
- Abdominal distention: Associated with larger tumors or advanced disease 1
Systemic Symptoms
- Fatigue and weakness: Common due to chronic blood loss and anemia 1, 3
- Anorexia: More associated with proximal (right-sided) colon cancers 3
Location-Specific Symptom Patterns
Distal/Left-Sided Colon and Rectal Cancers
- More likely to present with rectal bleeding (38% of hematochezia cases are rectal cancers) 1, 2
- Constipation is more predictive of distal location 3
- Anorectal stimulating symptoms occur in 17.3% of cases 4
Proximal/Right-Sided Colon Cancers
- More likely to present with iron deficiency anemia (20% of anemia cases) 1, 2
- Proximal symptoms including anorexia, nausea, vomiting, and abdominal pain 3
Critical Clinical Context
Symptom Combinations Increase Risk
- One red-flag symptom: 1.9-fold increased risk 2
- Two red-flag symptoms: 3.6-fold increased risk 2
- Three or more symptoms: 6.5-fold increased risk 2
- Multiple symptoms at presentation: Occurs in 44-50.8% of cases 2, 4
Timing and Stage Considerations
- Symptoms indicate relatively advanced disease: Most symptomatic patients present with larger tumors and/or advanced stages (>50% are stage IIb or later at symptom onset) 1, 4
- Median symptom duration before diagnosis: 14 weeks (range 5-43 weeks), though duration does not correlate with stage 3
- Number of symptoms inversely related to survival: More symptoms at presentation correlate with worse prognosis 1
Critical Pitfalls to Avoid
Do NOT Use FIT Testing for Symptomatic Patients
- Fecal immunochemical testing (FIT) should NEVER replace colonoscopy in patients with alarm symptoms, as it delays diagnosis and increases risk of advanced-stage disease 1, 2, 6
Do NOT Dismiss Non-Specific Symptoms
- While abdominal pain and change in bowel habits alone have limited specificity, when combined with other alarm symptoms, they significantly increase cancer risk 1, 2, 5
- Do not attribute symptoms to benign conditions (hemorrhoids, IBS) without proper colonoscopic evaluation, especially in patients ≥45 years 1, 7
Do NOT Delay Based on Age
- Patients ≥45 years with new-onset symptoms require colonoscopy regardless of symptom type 7
- Younger patients (<45 years) with alarm symptoms also require immediate colonoscopy 1, 6
Diagnostic Approach
Immediate Colonoscopy Required For:
- Any patient with hematochezia, unexplained iron deficiency anemia, or unexplained weight loss 1, 2
- Colonoscopy must be complete to the cecum to detect synchronous lesions (present in 2.5% of cases) 1, 2, 6