What are the signs and symptoms of colon cancer?

Signs and Symptoms of Colon Cancer

The most common symptoms of colon cancer are change in bowel habits, abdominal pain, rectal bleeding, weakness, iron deficiency anemia, and unexplained weight loss—though symptoms typically indicate relatively large tumors or advanced disease stages. 1

High-Specificity Alarm Features

Only two symptoms have >95% specificity for colon cancer and strongly indicate the diagnosis:

• Dark red rectal bleeding (specificity >95%) 1
• Palpable abdominal mass (specificity >95%) 1

These findings from a systematic review and meta-analysis of over 19,000 cases should prompt immediate colonoscopy. 1

Common Presenting Symptoms

The following symptoms are frequently present but less specific for colon cancer:

• Rectal bleeding/hematochezia (45-58% of cases) 2, 3
• Abdominal pain (35-52% of cases) 2, 3
• Change in bowel habits (27-51% of cases), including altered stool caliber 2, 3
• Iron deficiency anemia (57-60% of cases) 2, 3
• Occult blood in stool (77% of cases) 3
• Unexplained weight loss 1
• Weakness and fatigue 1

Critical Red-Flag Symptoms for Early-Onset CRC (Age <50)

For patients younger than 50 years, four symptoms are particularly associated with increased risk:

• Abdominal pain (OR 1.34-2.23) 1, 4
• Rectal bleeding (hazard ratio 10.66) 1, 4
• Diarrhea (OR up to 5.13) 4
• Iron deficiency anemia (hazard ratio 10.81) 1, 4

Having multiple red-flag symptoms dramatically increases risk: 1 symptom confers 1.94-fold risk, 2 symptoms confer 3.59-fold risk, and ≥3 symptoms confer 6.52-fold risk. 4 The association is stronger in younger patients and for rectal cancers. 4

Location-Specific Symptom Patterns

Distal/left-sided colon and rectal cancers (75% of obstructing cancers) present with:

• Blood in stool (OR 4.37 for rectal vs. colon cancer) 5
• Changes to stool consistency or caliber (OR 1.78 for rectal cancer) 5
• Constipation (OR 3.16 for distal location) 3

Proximal/right-sided colon cancers present with:

• Abdominal pain (OR 0.30 for rectal vs. colon) 5
• Anemia (OR 0.40 for rectal vs. colon) 5
• Often more subtle or "proximal symptoms" (anorexia, nausea, vomiting) 3

Important Clinical Caveats

Symptoms are generally non-specific and associated with worse prognosis: 1

• The number (but not duration) of symptoms inversely correlates with survival 1
• Median symptom duration before diagnosis is 14 weeks (range 5-43 weeks) 3
• No association exists between symptom duration and tumor stage 3
• Early-stage cancers (Dukes' A) still present with significant symptoms in >50% of cases 2, 6

Early colon cancer produces minimal or no symptoms, which is why screening asymptomatic individuals remains essential for detecting early-stage disease. 1 Approximately 90% of cancers are not diagnosed until they have penetrated through the bowel wall or spread to lymph nodes. 1

Synchronous and metachronous tumors occur: 2.5% of patients have synchronous lesions at diagnosis, and up to 9% develop metachronous tumors over decades, necessitating complete colonoscopy and long-term surveillance. 1

Diagnostic Timing Considerations

Approximately 19.3% of early-onset CRC patients experience their first symptom 3-24 months before diagnosis (median diagnostic interval 8.7 months), while 49.3% have symptoms within 3 months of diagnosis (median interval 0.53 months). 4 Colonoscopy should ideally be performed within 30 days of presentation with alarming symptoms to prevent diagnostic delays that contribute to advanced-stage disease. 1