Etiology and Risk Factors for Rectal Cancer
Molecular Pathogenesis
- The majority of rectal cancers arise through the chromosomal instability (CIN) pathway, characterized by sequential accumulation of mutations in tumor‑suppressor genes and oncogenes. 1
- The WNT signaling pathway is the principal molecular driver in rectal carcinogenesis, with frequent mutations in the APC tumor‑suppressor gene. 2
- Inactivation of TP53 and TGF‑β tumor‑suppressor pathways together with activation of oncogenes such as KRAS and PI3KCA contributes to tumor development. 2
- Approximately 13 % of rectal cancers are attributable to deficient mismatch repair (dMMR); microsatellite instability is uncommon in this site. 1
- About one‑third of rectal cancers display aberrant DNA methylation patterns. 2
- BRAF mutations occur rarely in rectal cancer, distinguishing it from colon cancer. 2
Hereditary Factors
- Up to 15 % of rectal cancer cases have a hereditary component, though the contribution is greater for colon cancer. 2
- Lynch syndrome and familial adenomatous polyposis are the most common hereditary syndromes associated with rectal cancer, warranting genetic counseling for affected families. 1
- Roughly 40 common low‑penetrance colorectal‑cancer risk alleles have been identified; rare high‑penetrance variants add an additional ~16 % to hereditary risk. 3
Modifiable Risk Factors – Dietary
- High consumption of red or processed meat increases the risk of rectal cancer. 1
- Higher intake of dietary fiber is likely protective against rectal cancer. 2
- Consumption of garlic, milk, calcium, and foods rich in fiber is regarded as protective. 1
- Adherence to high‑quality dietary patterns, as measured by diet‑quality indices, is associated with a lower risk of colorectal cancer. 4
Modifiable Risk Factors – Lifestyle
- Tobacco smoking elevates the risk of rectal cancer. 1
- Moderate to heavy alcohol use raises rectal cancer risk. 1
- Physical inactivity is a significant risk factor, whereas regular exercise and a healthy lifestyle substantially reduce risk. 1
- Elevated body mass index or abdominal obesity increase rectal cancer risk. 1
Modifiable Risk Factors – Metabolic
- Type II diabetes is associated with an increased risk of rectal cancer, likely mediated by hyperinsulinemia and insulin‑like growth factors. 1
Medical Conditions
- Long‑standing ulcerative colitis and Crohn’s disease involving the rectum increase the risk of rectal cancer. 1
Demographic Factors
- Risk of rectal cancer rises with age; the median age at diagnosis is approximately 70 years. 1
- Incidence is projected to increase in both sexes, with the median age at diagnosis expected to shift upward. 1
Protective Factors
- Regular use of non‑steroidal anti‑inflammatory drugs (NSAIDs) is linked to a reduced incidence of rectal cancer, although formal primary‑prevention guidelines are lacking. 1
- Vitamin D may confer a protective effect through antitumor immunity, but evidence regarding supplementation remains mixed. 1
Distinctions from Colon Cancer
- Emerging evidence indicates that rectal cancer is etiologically distinct from colon cancer, reflecting different environmental exposures and molecular characteristics. 1
Knowledge Gaps
- The interplay among genetic susceptibility, gut microbiome, epigenetic alterations, and environmental factors in rectal cancer remains poorly characterized. 3
Rectal Cancer Diagnosis and Treatment
Introduction to Rectal Cancer
- Rectal cancer is defined as tumors with distal extension to ≤15 cm from the anal margin, while tumors beyond 15 cm are classified as colonic, according to the American Joint Committee on Cancer 5, 6, 7
Anatomical and Embryological Differences
- The rectum and colon have different embryological origins, which contributes to their distinct biological behaviors, as stated by the National Comprehensive Cancer Network 5, 6
- Rectal cancers are further subdivided into low (up to 5 cm), middle (>5 to 10 cm), and high (>10 to 15 cm from anal verge), with each requiring different surgical approaches, as recommended by the American College of Surgeons 5, 6
Epidemiological and Risk Factor Differences
- Evidence is accumulating that rectal cancer is distinct from colon cancer with different aetiologies and risk factors, possibly reflecting different environmental exposures, according to the International Agency for Research on Cancer 5, 6
- The hereditary component is more pronounced for colon cancer than rectal cancer, as stated by the American Society of Clinical Oncology 5, 8
Molecular and Pathological Differences
- Unique transcriptional subtypes with high Wnt signaling, stem cell and mesenchymal signatures occur specifically in rectal cancer and carry a poor prognosis, as reported by the National Cancer Institute 5, 6
- Microsatellite instability (MSI) is very rare in rectal cancer (only a few percent), whereas it occurs in about 13% of cases overall when considering both sites, according to the College of American Pathologists 5, 8
Critical Treatment Differences
- Rectal cancer requires specialized local staging with endoscopic rectal ultrasound (ERUS) or rectal MRI to determine the need for neoadjuvant therapy and surgical approach, as recommended by the European Society for Medical Oncology 6, 7, 8
- Neoadjuvant chemotherapy and radiation added to primary resection in patients with high-risk rectal cancer has been shown to decrease local recurrence and improve survival, according to the American Society for Radiation Oncology 9
- Rectal cancer requires total mesorectal excision (TME) for mid-to-low tumors, a specialized technique involving sharp dissection along the mesorectal fascia, as stated by the American College of Surgeons 10
Surveillance Differences
- Surveillance colonoscopy strategies differ between rectal and colon cancer due to the higher local recurrence rates in rectal cancer, as recommended by the American Gastroenterological Association 10
- Many clinicians perform more intensive local surveillance for rectal cancer patients, particularly examining the anastomosis or rectal remnant, whereas this is generally not undertaken for colon cancer, according to the National Comprehensive Cancer Network 10