Is rectal cancer considered the same as colon cancer?

Rectal Cancer is NOT the Same as Colon Cancer

Rectal cancer and colon cancer are distinct disease entities that should be considered separately, not as a single "colorectal cancer" diagnosis, despite their anatomic proximity. 1

Key Distinctions Between Rectal and Colon Cancer

Anatomical and Embryological Differences

• Rectal cancer is defined as tumors with distal extension to ≤15 cm from the anal margin (measured by rigid sigmoidoscopy), while tumors beyond 15 cm are classified as colonic. 1

• The rectum and colon have different embryological origins, which contributes to their distinct biological behaviors. 2

• 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. 1

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. 1

• The hereditary component is more pronounced for colon cancer than rectal cancer. 1

• Physical activity helps prevent colon cancer but not rectal cancer, and the risk of developing rectal cancer is four times higher than colon cancer anatomically. 3

Molecular and Pathological Differences

• While The Cancer Genome Atlas showed common genomic profiles for non-hypermutated colon and rectal cancers, unique transcriptional subtypes with high Wnt signaling, stem cell and mesenchymal signatures occur specifically in rectal cancer and carry a poor prognosis. 1

• 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. 1

• BRAF mutations are rare in rectal cancer but more common in proximal colon cancers. 2

• EGFR is prevalently amplified or overexpressed in distal colorectal cancers (including rectal), while BRAF is preferentially mutated in proximal colon cancers. 2

Critical Treatment Differences

The most important clinical distinction is that rectal and colon cancer require fundamentally different treatment approaches:

Staging Requirements

• Rectal cancer requires specialized local staging with endoscopic rectal ultrasound (ERUS) or rectal MRI to determine the need for neoadjuvant therapy and surgical approach. 1

• Colon cancer staging focuses primarily on identifying advanced T stage and distant metastases, with locoregional nodal staging being of marginal clinical utility since neoadjuvant therapy has not been shown to significantly improve survival over surgery alone. 1

Neoadjuvant Treatment

• Neoadjuvant radiotherapy or chemoradiotherapy is administered solely for rectal cancer (particularly mid-to-low rectal tumors), not for colon cancer. 2

• 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. 1

• High rectal cancers (10-15 cm from anal verge) may not require routine preoperative chemoradiotherapy and can be treated more like colon cancer. 4

Surgical Approaches

• Rectal cancer requires total mesorectal excision (TME) for mid-to-low tumors, a specialized technique involving sharp dissection along the mesorectal fascia. 1

• High rectal tumors undergo wide mesorectal excision with removal of at least 5 cm of rectal mesentery, rather than complete TME. 4

• Colon cancer treatment relies primarily on radical hemicolectomy based on tumor location (right versus left), with removal of associated mesentery and regional nodes. 1

• Surgical options for rectal cancer are more varied and depend on the relationship of tumor to the sphincter and circumferential resection margins, with sphincter preservation being a critical consideration. 1, 5

Local Recurrence Patterns

• Local recurrence rates for rectal cancer can be 10 or more times higher than colon cancer, where anastomotic recurrence occurs in only 2-4% of patients. 1

• Risk of pelvic recurrence is higher in patients with rectal cancer compared with colon cancer, and locally recurrent rectal cancer is associated with a poor prognosis. 1

Surveillance Differences

• Surveillance colonoscopy strategies differ between rectal and colon cancer due to the higher local recurrence rates in rectal cancer. 1

• 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. 1

Clinical Implications

The term "colorectal cancer" should be abandoned in clinical practice, research, and classification systems because treating these as a single entity leads to suboptimal care. 3

• Despite their differences in metastatic pattern, composition of drug targets, and earlier local treatment, metastatic rectal and colon cancer are commonly regarded as one entity and treated alike—this practice should be reconsidered. 2

• Future clinical trials with targeted drugs should be designed separately for rectal versus colon cancer given their distinct molecular profiles. 2

• A specialized multidisciplinary team should discuss all rectal cancer cases to determine optimal sequenced multimodality therapy combining chemoradiotherapy, chemotherapy, and operative treatment. 1