# Colorectal Cancer: Surgical Principles

## Epidemiology

Colorectal cancer is the third most common cancer worldwide and the second leading cause of cancer death. The lifetime risk is approximately 4-5% in average-risk individuals. Notably, the incidence in patients under age 50 is rising, which has prompted earlier screening recommendations (beginning at age 45, per the 2021 USPSTF update). Approximately 70% of colorectal cancers arise in the colon, with the remaining 30% occurring in the rectum.

## Staging and Workup

### TNM Staging (AJCC 8th Edition)

The AJCC TNM system classifies tumor depth as follows:

| T Stage | Depth of Invasion |
|---------|------------------|
| T1 | Submucosa |
| T2 | Muscularis propria |
| T3 | Through muscularis into pericolorectal tissues |
| T4a | Penetrates visceral peritoneum |
| T4b | Directly invades adjacent organs/structures |

| N Stage | Positive Lymph Nodes |
|---------|---------------------|
| N0 | 0 |
| N1 | 1–3 |
| N2 | ≥4 |

T1 denotes invasion of the submucosa, T2 invasion of the muscularis propria, T3 invasion through the muscularis propria into pericolorectal tissues, T4a penetration of the visceral peritoneum, and T4b direct invasion of adjacent organs or structures. Nodal staging is based on the number of positive regional lymph nodes, with N1 indicating 1-3 positive nodes and N2 indicating 4 or more. A minimum of 12 lymph nodes must be examined for adequate staging.

### Preoperative Workup

The preoperative workup begins with colonoscopy and biopsy for tissue diagnosis, followed by CT of the chest, abdomen, and pelvis with contrast for staging. A baseline CEA level should be obtained as both a prognostic and surveillance marker. For rectal cancer, a pelvic MRI is mandatory, and endorectal ultrasound may provide additional information. PET-CT is not routinely indicated for initial staging but is used selectively for suspected metastatic disease. Microsatellite instability and mismatch repair testing should be performed on all colorectal cancer specimens, and RAS/BRAF mutation testing is performed for metastatic disease.

<image>CT scan showing a circumferential sigmoid colon mass with pericolonic lymphadenopathy and liver metastasis demonstrating stage IV colorectal cancer</image>

## Colon Cancer -- Surgical Principles

### Oncologic Resection Principles

The goals of curative surgery are en bloc resection of the tumor with adequate margins and regional lymphadenectomy. Proximal and distal margins should be at least 5 cm, though the radial margin is generally more important. High ligation of the primary feeding vessel is performed to achieve an adequate lymph node harvest. The no-touch isolation technique, in which vessels are ligated before tumor manipulation, has a theoretical benefit but is not proven. A minimum of 12 lymph nodes should be retrieved for adequate staging.

### Complete Mesocolic Excision (CME)

Complete mesocolic excision involves sharp dissection in the embryologic planes, keeping the mesocolic fascia intact, with central vascular ligation at the origin of the feeding vessels. This approach is analogous to total mesorectal excision for rectal cancer and was pioneered by Hohenberger. CME improves lymph node harvest and may yield better oncologic outcomes, though its adoption varies worldwide.

### Standard Resections by Tumor Location

The extent of colonic resection is determined by the tumor's location and its arterial blood supply. Tumors of the cecum and ascending colon are treated with a right hemicolectomy, encompassing the ileocolic, right colic, and right branch of the middle colic artery. Hepatic flexure tumors require an extended right hemicolectomy. Transverse colon tumors are managed with a transverse colectomy or extended right hemicolectomy based on the middle colic artery. Splenic flexure tumors may require a splenic flexure resection or extended left or right hemicolectomy. Descending colon tumors warrant a left hemicolectomy, sigmoid tumors a sigmoid colectomy, and synchronous cancers may require a subtotal or total colectomy depending on location.

### Laparoscopic vs. Open

Laparoscopic colectomy is the standard of care for colon cancer. The COST, COLOR, and CLASICC trials have demonstrated equivalent oncologic outcomes with faster recovery, reduced wound complications, shorter hospital stays, and less postoperative pain. The robotic-assisted approach has seen growing adoption but has not demonstrated proven superiority over standard laparoscopy.

### Emergent Presentation

Patients presenting with obstruction may undergo resection with primary anastomosis or a Hartmann procedure depending on clinical status, or alternatively proximal diversion followed by a delayed resection. Perforation is managed with resection, with or without anastomosis depending on the level of contamination. Self-expanding metal stents can serve as a bridge to surgery for left-sided malignant obstruction, allowing time for bowel preparation and a single-stage operation, though concerns exist about tumor seeding and perforation.

## Rectal Cancer -- Surgical Principles

### Anatomic Considerations

The rectum measures approximately 12-15 cm from the anal verge and is divided into upper (10-15 cm), middle (5-10 cm), and lower (0-5 cm) thirds. The mesorectum is the perirectal fat envelope that contains lymph nodes and blood vessels. The circumferential resection margin is a critical prognostic factor, as a positive CRM (less than 1 mm) significantly increases local recurrence.

### Total Mesorectal Excision (TME)

Total mesorectal excision, pioneered by Heald, is the gold standard for mid and low rectal cancer. The technique involves sharp dissection in the avascular "holy plane" between the mesorectal fascia and the parietal pelvic fascia, yielding a complete, intact mesorectal envelope without coning or tears. Nerve-sparing technique, which preserves the hypogastric nerves and pelvic plexus, is essential. The quality of the TME specimen -- graded as complete, near-complete, or incomplete -- is a key quality indicator.

### Tumor-Specific Mesorectal Excision

For upper rectal cancers located more than 10 cm from the anal verge, a tumor-specific mesorectal excision with a 5 cm distal mesorectal margin is performed rather than a full TME. For mid and low rectal cancers, a complete TME is required.

### Surgical Options for Rectal Cancer

Low anterior resection involves TME with a colorectal or coloanal anastomosis. A diverting loop ileostomy is recommended for low anastomoses to reduce the clinical impact of any leak. Construction of a colonic J-pouch or side-to-end anastomosis improves functional outcomes.

Abdominoperineal resection involves TME with a permanent end colostomy and is reserved for very low tumors where sphincter preservation is not feasible. The extralevator APR provides a wider perineal dissection to reduce positive CRM rates.

Intersphincteric resection is an option for very low tumors at the dentate line, preserving the external sphincter and allowing coloanal anastomosis. This requires careful patient selection and thorough counseling about functional outcomes.

Local excision via transanal excision or TAMIS/TEM is appropriate for selected T1 tumors that are less than 3 cm, involve less than 30% of the circumference, are well or moderately differentiated, lack lymphovascular invasion, and show only superficial submucosal invasion. Local excision has higher local recurrence rates than TME, requiring close surveillance, and completion TME is performed if the excision specimen reveals adverse pathologic features.

<image>Sagittal MRI of the pelvis showing a mid-rectal cancer with mesorectal lymph node involvement and the mesorectal fascia delineating the circumferential resection margin</image>

### Neoadjuvant Therapy for Rectal Cancer

Neoadjuvant therapy is standard for locally advanced rectal cancer (cT3-4 or cN+). Options include long-course chemoradiation (5-FU or capecitabine with 50.4 Gy over 5-6 weeks, followed by surgery 6-10 weeks later), short-course radiation (25 Gy in 5 fractions, with surgery within one week or delayed 6-8 weeks), and total neoadjuvant therapy (TNT), in which all systemic chemotherapy and radiation are delivered before surgery. The RAPIDO, PRODIGE 23, and OPRA trials support the TNT approach, which yields higher pathologic complete response rates and allows assessment of tumor biology.

### Watch-and-Wait (Organ Preservation)

For patients achieving a clinical complete response after neoadjuvant therapy -- defined by no residual tumor on digital rectal examination, endoscopy, and MRI -- a watch-and-wait strategy may be pursued. Intensive surveillance includes DRE, endoscopy, and MRI every 3-6 months. The OPRA trial demonstrated an organ preservation rate of approximately 50% with TNT. Salvage surgery for local regrowth remains feasible, with 90% of cases amenable to R0 resection. This approach is not yet standard of care and should be discussed in a multidisciplinary team, preferably within a protocol.

### Low Anterior Resection Syndrome (LARS)

LARS is a cluster of symptoms that develops after low rectal resection, including urgency, frequency, incontinence, clustering, and incomplete evacuation. It affects 50-80% of patients to some degree. Risk factors include a low anastomosis, prior radiation, and coloanal (versus colorectal) anastomosis. Management options include dietary modification, pelvic floor therapy, biofeedback, tibial nerve stimulation, and sacral nerve stimulation. Construction of a colonic J-pouch reduces the severity of LARS.

<image>Total mesorectal excision specimen showing intact mesorectal envelope with smooth peritoneal surface and no defects in the mesorectal fascia, demonstrating a complete TME grade</image>

## Molecular and Genetic Considerations

Microsatellite instability-high (MSI-H) or mismatch repair-deficient (dMMR) tumors comprise about 15% of colorectal cancers. These tumors carry a better prognosis in early-stage disease and predict response to immunotherapy in advanced disease. Lynch syndrome, caused by germline mutations in MMR genes, is identified by screening all colorectal cancer patients with immunohistochemistry or MSI testing. Familial adenomatous polyposis, caused by APC gene mutations, requires prophylactic colectomy. KRAS and NRAS mutations predict resistance to anti-EGFR therapy, and the BRAF V600E mutation carries a poor prognosis but may respond to targeted therapy with encorafenib and cetuximab.

## Adjuvant Therapy

Stage I disease requires surgery alone. For stage II disease, observation is generally appropriate, though adjuvant FOLFOX may be considered for high-risk features such as T4 stage, poor differentiation, lymphovascular invasion, perineural invasion, inadequate lymph node harvest, or presentation with obstruction or perforation. MSI-H stage II tumors carry an excellent prognosis, and 5-FU may actually be detrimental, so observation is preferred. Stage III disease is treated with adjuvant chemotherapy as the standard of care. The IDEA collaboration established that low-risk patients (T1-3, N1) can receive 3 months of FOLFOX, while high-risk patients (T4 or N2) should receive 6 months. CAPOX for 3 months has been shown to be non-inferior to 6 months for low-risk stage III disease.

## Clinical Pearls

A minimum of 12 lymph nodes must be examined for adequate staging, and if the pathology report shows fewer, communication with the pathologist is warranted. For rectal cancer, pelvic MRI is mandatory because it determines the treatment plan, including whether neoadjuvant therapy or upfront surgery is indicated. The quality of the TME specimen is the single most important surgical factor in preventing local recurrence of rectal cancer. CRM positivity (less than 1 mm) is the strongest predictor of local recurrence, and surgeons should strive for a negative CRM. Total neoadjuvant therapy is changing the paradigm for rectal cancer, with higher pathologic complete response rates and potential for organ preservation. All patients should be tested for MSI/MMR, as this affects prognosis, adjuvant therapy decisions, and identifies Lynch syndrome families. Patients with low rectal cancer should be counseled about LARS before surgery, as it is very common and significantly impacts quality of life.

## References
- Heald RJ, et al. The mesorectum in rectal cancer surgery -- the clue to pelvic recurrence? Br J Surg. 1982;69(10):613-616.
- Hohenberger W, et al. Standardized surgery for colonic cancer: Complete mesocolic excision and central ligation. Surg Today. 2009;39(12):1000-1008.
- Clinical Outcomes of Surgical Therapy Study Group. A comparison of laparoscopically assisted and open colectomy for colon cancer. N Engl J Med. 2004;350(20):2050-2059.
- Garcia-Aguilar J, et al. Organ preservation in patients with rectal adenocarcinoma treated with total neoadjuvant therapy (OPRA). J Clin Oncol. 2022;40(23):2546-2556.
- Andre T, et al. Effect of duration of adjuvant chemotherapy for patients with stage III colon cancer (IDEA). Lancet Oncol. 2020;21(12):1620-1629.