Surgery of colon cancer
Curative resections can be performed by laparotomy or laparoscopy. Large studies have shown that both techniques are equivalent with regard to oncological result and complications. Regardless of operative approach the same surgical principles applies. Adequate resections implies removal of the tumor containing bowel segment, regional mesentery with lymph nodes, dissection in the correct plane around bowel and mesentery , with technique which will secure R0-resection.
Lymph node dissection
The regional lymph nodes are classified in three groups according to the localization: Bowel near (N1), intermediary (N2) and central (N3). The similar terminology to describe the extension of the lymph node dissection is D1-, D2- and D3- dissection (“high tie”).
For all curative resections a complete D2-resection should be performed as a minimum. There is no definite proof that D3- dissection will secure better result than D2-dissection, but there are several good reasons suggesting that D3- dissection should be the gold standard:
- 2-4% of all patients have central lymph node metastases without simultaneous distant metastases. These patients can be potentially cured by a D3-dissection but will have regional recurrence after D2-dissection.
- Several studies show that a higher number of examined lymph nodes in the specimen results in a better prognosis. Even though this may be due to various reasons, it probably also suggests that an extensive lymph node dissection is beneficial.
- Centers performing D3-dissections as a standard report good results.
It has been customary to resect the tumor containing bowel segment including 10 cm free margin orally and anally. However, 5 cm is also considered adequate in the large bowel. From an oncological point of view we therefore recommend 10 cm free margin on the bowel and the pericolic lymph nodes in all segments of the large bowel except at the rectosigmoid flexure where 5 cm is adequate anally. The extent of the resection will in addition be decided from the anatomy of the vessels and the circulatory conditions of the bowel after the lymph node dissection and central vascular ligation has been performed.
Dissection around the primary cancer in the pericolic plane:
As in the rectum, where there is a defined plane (often called “the holy plane”) on the outside of the mesorectal fascia, there is a defined retroperitoneal plane in all segments of the colon. This plane is in between the back of the visceral mesocolon and the parietal part of the peritoneum. By careful dissection this plane may be followed around the whole extent of the colon. When the bowel has been mobilized the mesocolon will be intact and include colon containing the primary tumor, all lymph vessels, lymph nodes and blood vessels.
The anterior part of this “package” is covered by peritoneum, the dorsal aspect by a mesocolic “fascia”. If this “package” is traumatized or dissected into the possibility of spread or leaving behind viable cancer cells similar to the rectal procedure. Dissection in the correct plane is important in the circumference around the primary tumor and in the central parts of the mesentery.
A study for Leeds in England has shown that the “mesocolic plane” is damaged in more than half of the specimens after “standard” resection. Cases with intact mesocolic fascia had better prognosis than patients where this was injured and the dissection had entered the outer part of the bowel wall.
Hohenberger (Erlangen) has systematized and described the dissection around the primary tumor and the adjoining mesentery and has introduced the notion “complete mesocolic excision”. He will always combine this with D3-dissection of lymph nodes and has reported excellent results. In a comparative study a far higher percentage of intact “oncological package” was found after operation in Erlangen than in Leeds (92% vs 40%).
When the tumor infiltrates adjacent organs an en-bloc resection should be performed with resection of the relevant organ(s) avoiding contact with tumor tissue. An en-bloc R0-resection can have nearly identical prognosis as for tumors not involving neighbouring organs. Dissection into tumor will dramatically reduce the prognosis. Biopsy should be performed in case remaining tumor is considered. Areas with unresectable tumor should be marked with metal clips for identification of the area in case of later irradiation.
Iatrogenic perforation of the bowel close to tumor is extremely rare in cases of colon cancer. More commonly the tumor perforates preoperatively. This will entail a worse prognosis and such patients should therefore be considered for adjuvant oncological treatment.
Surgical treatment has two phases:
- Resection of the tumor. In this phase, the least amount of manipulation of the tumor as possible is done before all veins draining the tumor are ligated to reduce spreading of liberated cancer cells by circulation.
- Reconstruction of function and closing of abdominal wall/peritoneum.
There is a direct correlation between surgical technique and prognosis for rectal cancer. This is not to the same extent for colon cancer.
There is also a clear correlation between acute surgery and postoperative complications. Acute cancer surgery should therefore be avoided when possible.
Early stage cancer
Treatment of T1 tumor in pedunculated polyp
- T1 tumors in pedunculated polyps, Haggitt level 1 and 2, are curatively removed by endoscopic loop resection when there is a microscopic free resection margin.
- With Haggitt level 3, the resection margin will often be uncertain. In the rectum, a resection with TEM can be performed and histology will determine whether this treatment is sufficient. In the colon, a formal resection is performed.
- Hagitt level 4 is treated as a sessile tumor.
Treatment of T1 sessile tumors in the rectum
There is no consensus on treatment for these patients. Local resection using TEM as a curative treatment is an alternative if the following criteria are filled:
- The tumor is less than 2.5-3 cm in diameter.
- The tumor is of high or moderate differentiation.
- The tumor is not infiltrating deeper than to the upper part of the submucosa (Kikuchi sm1).
- For sm2, the situation is assessed individually.
- There is no sign of infiltration in the vein/lymph systems.
- The tumor lies in an area of the rectum where a full wall resection can be performed such that a 1 cm free margin is achieved sideways (in the mucosa/intestinal wall around the tumor).
The diagnostic evaluation should aim at determining whether the criteria are met before the operation. However, the final result depends on the histological examination of the TEM specimen. If all criteria are not met, then patients in good general health status should be re-operated with a formal rectum resection (TME) within a few weeks. The patient should be informed about this before the TEM operation.
If all criteria are met, the risk for local recurrence is less than 10%. The patient must be monitored closely by rectal exploration, endoscopy, and rectal ultrasound. Possible recurrence can then be found at an early stage such that a curative operation is possible.
Localized cancer (T1-T3)
When the cancer is localized, the bowel segment including mesorectum can be removed with the tumor and the local lymph node stations along the veins. For radical surgery, draining lymph nodes must be removed along with the tumor. This will determine the length of the bowel that has to be removed. Cutting into the tumor must be avoided as this will increase the chance of spreading cancer cells.
Locally advanced cancer (T4a)
In locally advanced cancer, the bowel segment is removed with the infiltrated organ in en-bloc. A problem is that in approximately 25% of patients, fixation to surrounding tissue is caused by an inflammatory reaction and not direct cancer infiltration. To be certain of removing the tumor with wide enough margins, one risks removing organs which the pathology examination shows were not infiltrated with cancer. "Trial excision" through the tumor between two organs may free cancer cells and reduce the prognosis. If tumor has infiltrated neighboring organs/structures, these must be removed en bloc. In around 70% of cases, there are cancer cells in infiltrated neighboring organs even if radiation therapy or chemotherapy is given. The patient must be operated at the level the tumor was before treatment and remove fibrosis and mucinous areas if the treatment is intended to cure the disease.
In local relapse, estimation of the tumor limits are an even greater challenge. In such a case, free margins should also be achieved with extensive en bloc resections. However, a trial resection must often be performed with a frozen section biopsy of the resection edge to see if it is microscopically free.