What is colorectal cancer?

Colorectal cancer (CRC) includes cancers of the colon and rectum — the lower portion of the gastrointestinal tract. Over 90% are adenocarcinomas developing from adenomatous polyps over 10-15 years. CRC is the 3rd most common cancer globally (1.93M new cases in 2020) and the 2nd leading cancer killer (940K deaths). Incidence and mortality vary enormously by region — reflecting differences in dietary patterns, screening access and healthcare quality.

What causes colorectal cancer?

The main modifiable risk factors are: high intake of processed meat (WHO Group 1 carcinogen) and red meat (Group 2A); low dietary fibre; obesity and physical inactivity; alcohol; tobacco; and type 2 diabetes. Non-modifiable factors: age (>50); personal/family history of adenomatous polyps or CRC; Lynch syndrome and other hereditary syndromes; and long-standing inflammatory bowel disease (IBD). Approximately 70-80% of CRCs are sporadic; 20-30% have a hereditary component.

Why is colorectal cancer screening so effective?

CRC has a uniquely long pre-cancerous window — adenomatous polyps develop over 10-15 years before becoming invasive cancer. This window allows colonoscopy to detect and remove polyps before they become malignant. Stage I CRC has >90% 5-year survival vs 14% for stage IV. Faecal immunochemical test (FIT) detects blood from early lesions. Population-based screening programmes reduce CRC mortality by 30-50% — among the strongest cancer screening evidence of any malignancy.

Who should be screened for colorectal cancer?

Average-risk individuals: WHO and most guidelines recommend starting colonoscopy or FIT screening at age 45-50. High-risk individuals start earlier: first-degree relative with CRC (start 10 years before their diagnosis age); Lynch syndrome (colonoscopy every 1-2 years from age 20-25); inflammatory bowel disease (colonoscopy every 1-5 years after 8-10 years of disease). Family history of adenomatous polyps also increases risk.

Why is colorectal cancer rising in young adults?

CRC in adults under 50 has been increasing since the 1990s in high-income countries — now accounting for approximately 10-12% of new cases in the US. Proposed mechanisms: Western dietary patterns (high processed meat, low fibre); obesity; reduced physical activity; microbiome alterations; and potentially early-life antibiotic use. The trend preceded adoption of widespread colonoscopy screening. Young adults presenting with rectal bleeding or altered bowel habits should be evaluated without dismissing symptoms due to age.

What are the symptoms of colorectal cancer?

Common symptoms: change in bowel habits (persistent constipation, diarrhoea or alternating); rectal bleeding or blood in stool; abdominal pain or cramping; unexplained weight loss; fatigue (from anaemia); and a feeling of incomplete bowel emptying. Many early CRCs are asymptomatic — emphasising the importance of screening. Right-sided colon cancers more commonly present with iron deficiency anaemia; left-sided tumours cause altered bowel habits and rectal bleeding.

How is metastatic colorectal cancer treated?

Metastatic CRC treatment is guided by RAS/BRAF mutational status, MMR/MSI status and patient factors. Standard first-line: FOLFOX or FOLFIRI chemotherapy plus bevacizumab (anti-VEGF) for most patients; or cetuximab/panitumumab (anti-EGFR) for RAS wild-type tumours. MSI-H/dMMR tumours: pembrolizumab immunotherapy (highly effective). BRAF V600E mutations: BRAF inhibitor combination. Median overall survival has improved from approximately 6 months (1990s) to 24-30 months (2020s) in high-resource settings.

What is Lynch syndrome?

Lynch syndrome is the most common hereditary cancer syndrome — caused by germline mutations in DNA mismatch repair genes (MLH1, MSH2, MSH6, PMS2). It affects approximately 1 in 300 people but most are undiagnosed. Carriers have a 50-80% lifetime CRC risk, starting at younger ages (often 40s), plus elevated risks of endometrial, ovarian, gastric and urothelial cancers. Universal testing of all CRCs for MMR deficiency (immunohistochemistry or MSI PCR) identifies Lynch syndrome cases and guides therapy. Prophylactic aspirin (Lynch syndrome CAPP2 trial) reduces CRC risk.

What is the processed meat and CRC link?

The WHO/IARC classified processed meat as a Group 1 carcinogen and red meat as Group 2A — based on epidemiological evidence of approximately 18% increased CRC risk per 50g/day of processed meat consumed. Proposed mechanisms: nitrosamines from cured meat; haem iron promoting reactive oxygen species; and heterocyclic amines from high-temperature cooking. WHO recommends limiting processed meat consumption as part of cancer prevention.

How does the microbiome relate to CRC?

The gut microbiome is increasingly recognised as a CRC risk factor. Certain bacteria — particularly Fusobacterium nucleatum and enterotoxigenic Bacteroides fragilis — are overrepresented in CRC tissue and may promote tumour growth. Antibiotic use (altering the microbiome) and dietary patterns that affect the microbiome may contribute to the rising CRC incidence in young adults. Microbiome-based CRC risk biomarkers and microbiome modulation as prevention are active research areas.

How does GMJ News cover colorectal cancer?

GMJ News tracks GLOBOCAN CRC data, screening programme recommendations, the young adult CRC epidemic, Lynch syndrome awareness, and treatment advances including immunotherapy for MSI-H tumours. CRC burden in Georgia — where dietary patterns include significant processed meat and low fibre consumption — is a direct public health concern for PHIG and the Georgian Medical Journal.

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Colorectal Cancer

GMJ News knowledge hub · last reviewed September 2026 · Georgian Medical Journal

Summary Statistics Glossary GMJ news FAQ Documents Organizations Research

Colorectal cancer (CRC) is the third most common cancer globally and the second leading cause of cancer death: 1.93 million new cases and 940,000 deaths in 2020 — with incidence rising rapidly in younger adults, an alarming global trend reversing decades of progress (IARC/WHO). CRC is one of the most detectable and treatable cancers when diagnosed early — colonoscopy detects and removes pre-cancerous polyps before cancer develops, and early-stage 5-year survival exceeds 90%. Dietary risk factors (processed meat, low fibre), physical inactivity and obesity are major drivers; population-based screening programmes dramatically reduce mortality.

Key messages

3rd most common, 2nd deadliest

Colorectal cancer (CRC) — cancers of the colon and rectum — is the 3rd most common cancer globally with 1.93 million new cases, and the 2nd leading cause of cancer death with 940,000 deaths in 2020 (IARC GLOBOCAN 2020).

Screening transforms outcomes

CRC is one of the most effectively screened-for cancers: colonoscopy detects and removes adenomatous polyps before they become cancerous; faecal immunochemical test (FIT) detects blood in stool. Population-based screening reduces CRC mortality by 30-50%.

Rising in young adults

CRC incidence in adults under 50 has been rising sharply in high-income countries since the 1990s — an alarming trend driven by dietary patterns, obesity, microbiome changes and sedentary lifestyles. Young adults now account for approximately 10% of new cases in the US.

Diet and lifestyle modifiable

Major modifiable risk factors: consumption of processed and red meat; low dietary fibre; obesity; physical inactivity; alcohol; tobacco; and a history of inflammatory bowel disease. High-fibre diets, physical activity and weight control reduce CRC risk substantially.

Lynch syndrome

Lynch syndrome — a hereditary DNA mismatch repair deficiency — is the most common hereditary cancer syndrome, conferring 50-80% lifetime CRC risk. It affects approximately 1 in 300 people. Universal tumour testing for Lynch syndrome at CRC diagnosis is now recommended.

MSI/MMR and immunotherapy

Microsatellite instability-high (MSI-H) and mismatch repair deficient (dMMR) CRCs respond dramatically to immune checkpoint inhibitors (pembrolizumab). MSI/MMR testing guides therapy in metastatic CRC and — increasingly — in the adjuvant setting.

Key statistics

1.93M

new CRC cases/year (2020)

IARC GLOBOCAN

940K

CRC deaths/year (2020)

IARC GLOBOCAN

leading cause of cancer death

IARC

90%+

5-year survival — stage I

SEER

30-50%

mortality reduction with screening

Cochrane/USPSTF

1 in 300

people have Lynch syndrome

ESMO/ASCO

CRC age-standardised incidence rate (per 100,000) by world region — GLOBOCAN 2020

Source: IARC GLOBOCAN 2020. Highest rates in Australia, New Zealand and Europe; rising in East Asia.

Glossary of key terms

Adenoma / polyp
WHO/ACGPre-cancerous growths in the colon that can develop into colorectal cancer over 10-15 years. Adenomatous polyps (adenomas) are the main precursor. Colonoscopy detects and removes polyps, preventing their progression to cancer.

Faecal immunochemical test (FIT)
WHOA stool test detecting human haemoglobin — indicating blood in stool that may indicate colorectal neoplasia. Performed annually; positive results require diagnostic colonoscopy. Used as a first-line screening test in most national CRC screening programmes.

Lynch syndrome
ESMO/ASCOThe most common hereditary cancer syndrome — caused by germline mutations in mismatch repair genes (MLH1, MSH2, MSH6, PMS2, EPCAM). Confers 50-80% lifetime CRC risk and elevated risk of endometrial, ovarian, gastric and other cancers. Affects 1 in 300 people; most are undiagnosed.

Microsatellite instability (MSI)
ESMO/ASCOA marker of deficient DNA mismatch repair (dMMR) in CRC — found in approximately 15% of CRCs. MSI-H/dMMR CRCs respond dramatically to immune checkpoint inhibitors (pembrolizumab). Routine testing of all CRCs is now recommended for treatment guidance and Lynch syndrome detection.

FOLFOX/FOLFIRI
ESMO/ASCOStandard chemotherapy regimens for advanced CRC: FOLFOX (oxaliplatin, leucovorin, fluorouracil) or FOLFIRI (irinotecan, leucovorin, fluorouracil). Combined with bevacizumab (VEGF inhibitor) or cetuximab/panitumumab (EGFR inhibitors — for RAS wild-type tumours) in first-line metastatic treatment.

Inflammatory bowel disease (IBD)
WHO/ECCOCrohn's disease and ulcerative colitis substantially increase CRC risk — through chronic mucosal inflammation. Risk correlates with disease duration (>8-10 years), extent and severity. Surveillance colonoscopy every 1-5 years is recommended for long-standing IBD.