Surgery for colorectal cancer: Current trends

Preoperative staging assessments
The patient with colorectal cancer may present in many different ways, depending upon the extent and location of the primary tumor. The surgical approach to such patients will, therefore, vary according to the urgency and magnitude of the required intervention. Although preoperative staging may be hampered by the need for immediate intervention, in most situations, preoperative staging assessment is possible prior to surgery. Preoperative investigation for staging is particularly important in the management of rectal cancer.

The diagnosis and location of the tumor should be investigated by sigmoidoscopic or colonoscopic examination and biopsy. A preoperative metastatic survey includes chest X-ray and abdominal imaging by ultrasound, CT, or MRI. The entire colon should be assessed for synchronous neoplastic lesions using colonoscopy or barium enema. Synchronous colon polyps should be removed by colonoscopy or during resection of the primary colorectal cancer. Local invasion should be assessed by a CT scan of large colon tumors to plan for surgical management of extracolonic extension to adjacent organs such as duodenum, kidney, ureter or bladder, and large blood vessels.

Preoperative assessment of the extent of local invasion for rectal cancer is particularly important. Endorectal ultrasound, CT scan, or MRI is essential to determine the extent of local invasion and the presence or absence of mesorectal lymph nodes. Preoperative tumor staging will determine whether the lesion is amenable to local excision or whether preoperative radiation and chemotherapy should be recommended.

The clinical staging of colon cancer depends on a pathologic assessment of the resected tumor specimen. There is agreement across Canada to use the UICC (International Union Against Cancer) system (Table 1). This system depends on the degree of penetration of the bowel wall and the presence or absence of lymph nodes as the main determinant of prognosis in patients who do not have distant metastases. However, several other variables affect prognosis. Obstructing and perforated cancers have reduced survival rates.[1] Preoperative blood transfusion adversely affects survival from colorectal cancer, possibly by immunologic suppression.[2]

The prognosis may be poorer if the surrounding organs are invaded, but long-term survival is possible when en bloc resection of adjacent structures is achieved with clear resection margins. Prognostic markers under investigation include tumor-suppressor genes, (i.e., P53,DCC); DNA content, ploidy, and proliferation; and cell adhesion and recognition molecules. In the future these markers obtained at the time of initial biopsy could become essential for management decisions.[3]

Colon surgery
The extent of the colon cancer resection depends on the site of the primary tumor and whether the intent is for cure or palliation. In addition, subtotal colectomy or proctocolectomy may be considered for younger patients and patients with familial colon cancer or polyposis syndromes to decrease the likelihood of metachronous cancer. The extent of the resection should be decreased when age or infirmity worsens tolerance to diarrhea from a shortened bowel. Right colon cancer is treated by right hemicolectomy with nodal resection accompanying the ileocolic and right colic vessels.

Hepatic flexure lesions should be resected by extended right hemicolectomy with nodal resection accompanying the ileocolic, right colic, and middle colic vessels. Tumors of the transverse colon and the splenic flexure may be treated by subtotal colectomy and ileosigmoidostomy with nodal resection along the ileocolic, right colic, middle colic, and left colic vessels. Tumors of the descending and sigmoid colon are treated by hemicolectomy with nodal resection accompanying the left colic and sigmoid vessels. Proximal and distal resection margins for colon cancer should be 10 cm. Tumors adhering to surrounding structures should be resected en bloc with all or part of the surrounding structure to achieve a clear resection margin if clinically appropriate.

In postmenopausal women, oophorectomy should be considered. Occult ovarian metastases in Stage C colon cancers have been reported in up to 7% of cases. In addition, prophylactic oophorectomy can prevent ovarian cancer.

Rectal surgery
Major recent advances have improved our understanding of rectal anatomy and the biology of the extraluminal spread of rectal cancer. In addition, the end-to-end anastomotic stapling device has made it easier to perform lower rectal anastomosis. However, inadequate resection and injudicious use of these devices has resulted in an unacceptably high pelvic recurrence rate. Appropriate proximal, distal, and radial resection margins with nodal clearance encompassed within the mesorectal fascial envelope has resulted in pelvic recurrence rates of 10% or lower.[4] The technique of total mesorectal excision has been championed by Heald and is now accepted throughout the Western world. Total mesorectal excision should be performed for cancers of the middle and distal third of the rectum.

The technique involves resection of the rectum and entire mesorectum down to the pelvic floor with preservation of the pelvic sympathetic and parasympathetic nerves to preserve bladder and sexual function. Although a 2 cm distal margin is preferred, a margin of 1 cm is acceptable, since most rectal cancers do not exceed 1 cm of distal submucosal extension.[5] Cancer of the upper third of the rectum should be resected with generous subtotal mesorectal excision; the distal rectal resection margin should be 5 cm with accompanying subtotal mesorectal resection of at least 5 cm from the distal edge of the tumor. Tumors at or just above the sphincter mechanism are treated by abdominoperineal resection; total mesorectal excision is an essential part of this resection.

Favorable, small, superficial cancers (T1 and T2) of the middle and distal third of the rectum may be excised locally, followed by postoperative radiation. Characteristics favorable to local excision include small size (3 cm diameter and less than one-third of the rectal circumference); minimal invasion (preferably T1); and less aggressive histology (well or moderately well differentiated, absence of lymphatic or vascular invasion). At present, preoperative endorectal ultrasound is essential to determine the extent of penetration of the muscular wall and the presence or absence of perirectal lymph node metastases to assess the advisability of local excision.

Total mesorectal excision and sphincter-preserving anterior resection of the rectum requires coloanal reconstruction. Using a colonic “J-pouch.” improves bowel function after coloanal anastomosis. An end-to-side coloanal anastomosis such as the colonic J-pouch also decreases anastomotic leakage.[6] Sphincter-preserving resection of proximal third rectal cancers with subtotal mesorectal excision may be reconstructed using standard straight end-to-end or end-to-side anastomosis.

Issues regarding pre- and postoperative radiotherapy are discussed in Part I of this theme issue. Patients with tumors staged preoperatively as Stage II or Stage III benefit from a preoperative short course of radiation. This short course of preoperative radiation has been shown to decrease pelvic recurrence and improve survival, but with a decrease in the morbidity compared to radical radiotherapy. Patients who have clinical fixation or invasion of adjacent organs benefit from radical preoperative radiation and chemotherapy.

Recurrence and survival
Strategies regarding follow-up are addressed “Following up patients with colorectal cancer.” Resection of localized liver metastases is associated with 5-year survival of up to 30%.[7] Adverse prognostic factors affecting survival after resection of liver metastases include a short interval between the primary colorectal tumor resection and the salvage liver resection, presence of lymph node metastases, and presence of multiple liver metastases. Repeated resection of recurrent localized liver metastases is also of potential benefit. Resection of isolated pulmonary metastasis is associated with long-term survival in up to 30% of patients.[8]

Loco-regional recurrence may develop after complete resection in up to 19% of colon cancers and up to 33% of rectal cancers. As previously noted, the local recurrence rate for rectal cancer should be less than 10% with adequate surgical technique. Survival rate after loco-regional recurrence is less than 4% at 5 years. Re-resection of local recurrence is possible in some patients, with 5-year survival reported anywhere from 6% to 49% depending upon the location and extent of the recurrence. The decision to operate for recurrence is a difficult one, as the surgery required may be radical. The patient only benefits from repeated surgery if all disease can be resected with a free margin. 

Palliation for CRC
Decisions on the management of inoperable or disseminated disease are made as a team that includes the surgeon and radiation and medical oncologists. Resection of the primary colorectal cancer is recommended to palliate and prevent obstruction and bleeding, even in the presence of metastases. The decision to resect the primary colorectal cancer will be balanced upon the expected survival time from tumor burden and anticipation of symptomatic bleeding or obstruction from the primary colorectal tumor. Radiotherapy and chemotherapy may decrease symptomatic pain, bleeding, or obstruction. Preoperative chemoradiation may facilitate palliative tumor resection.

Other palliative techniques include transanal fulguration or laser therapy and stenting. Palliation of liver metastases may include systemic chemotherapy, hepatic arterial infusion, and embolization or local therapy including alcohol injection, radiofrequency ablation, and brachytherapy.

Dr McGregor is a clinical professor of surgery at UBC and a consultant surgeon at the BC Cancer Agency, Vancouver Centre. Dr Phang is an associate professor at UBC, UBC section head of colon and rectal surgery, a consultant surgeon at the BC Cancer Agency, Vancouver Centre, and head of general surgery at St Paul’s Hospital. Dr MacFarlane is a professor of surgery and director of post-graduate education at the UBC Department of Surgery, St Paul’s Hospital.