Colorectal adenocarcinoma is the third-most common of all cancer types, and is one of the leading indications for colectomy (Fig. 14.1). Most colorectal cancers arise from adenomatous polyps that become dysplastic, in what is known as the adenoma–carcinoma sequence. The progression from polyp to invasive cancer is a slow process, involving a series of genetic mutations, and takes approximately 10 years. As a result, screening colonoscopy with polypectomy, starting at age 50 years is highly effective at reducing the incidence of colon cancer.

Colonic tumors are generally asymptomatic in the early stages. Classically, it is taught that right-sided colon cancers present with blood per rectum, whereas left-sided tumors present with a decrease in stool caliber, however this is not always seen in clinical practice. Some patients may report shortness of breath or fatigue due to iron deficiency anemia brought on by occult bleeding from the tumor.

Once an endoscopic biopsy confirms the diagnosis of colon cancer, the next step is to stage the extent of disease. CT imaging of the chest and abdomen are obtained to evaluate for distant disease such as pulmonary or hepatic metastases. For colon cancers without metastases, patients proceed directly to surgical resection. Adjuvant chemotherapy is offered if nodal involvement is found on pathologic evaluation of the specimen, and in select node-negative patients with high-risk tumors.

On the other hand, if metastatic disease is already present at the time of diagnosis, most patients will be treated with systemic chemotherapy only. In select patients with a small burden of metastatic disease, resection of the primary tumor and a metastasectomy may be considered. This approach has been shown to prolong survival in well-selected patients with colon cancer.

Occasionally patients with colon cancer present with large bowel obstruction, due to a circumferential lesion that narrows the lumen of the bowel. These tumors are called apple core lesions, due to their imaging appearance on barium enema (Fig. 14.2). Endoscopic stenting should be the first treatment of choice for colonic decompression. If stenting is not possible, a diverting colostomy can be performed to relieve the obstruction. Resection of the tumor is not generally recommended in this setting since the obstructed proximal colon is dilated and may not be amenable to safe anastomosis. Once the obstruction has been relieved, the patients can continue with the staging work up and treatment as indicated.

Of note, colon cancer and rectal cancer have the same tumor histology and staging systems, however there are important differences in the treatment of these malignancies. Whereas patients with non-metastatic colon cancer proceed directly to surgical resection, patients with locally advanced rectal cancer should receive chemotherapy and radiation prior to surgery. This topic is described in greater detail in the section on rectal surgery.

The vast majority of colorectal cancers are sporadic, however there are also well-defined familial syndromes that increase an individual’s risk for developing cancer. Hereditary non-polyposis colorectal cancer (HNPCC), also known as Lynch Syndrome, is a familial cancer syndrome caused by gene mutation and is transmitted via an autosomal dominant pattern. Patients with this syndrome are at high risk for colon cancer as well as several other cancer types including endometrial, ureteral, ovarian, and gastric cancers. Colonic tumors in patients with HNPCC typically arise without a preceding polyp, making endoscopic surveillance less effective. Patients with HNPCC characteristically have right-sided tumors and more frequently have synchronous or metachronous cancers. Prophylactic colectomy is generally not indicated for individuals with Lynch Syndrome. However, once a colon carcinoma has developed it is recommended that the individual undergo subtotal colectomy at that time, to reduce the risk of future cancers.

Familial adenomatous polyposis (FAP) is caused by the loss of the APC tumor suppressor gene. The disorder is also transmitted via an autosomal dominant pattern; therefore, all family members of a diagnosed patient should also undergo screening. FAP results in innumerable colonic polyps that causes the near-certain development of colorectal cancer by the age of 45 years. Young individuals diagnosed with FAP should undergo prophylactic total proctocolectomy before age 25 years to prevent colon cancer development. It is important to note that in FAP the rectal mucosa is also at risk, and patients must undergo complete removal of the rectum in addition to the colon. Historically these patients underwent an abdominoperineal resection with end ileostomy. However, technical advances in surgery have led to the development of the ileal pouch that functions as a neo-rectum, and allows for preservation of bowel continuity. In patients with attenuated FAP who have rectal sparing, a subtotal colectomy with close rectal surveillance can be an option.

Ulcerative colitis is an inflammatory bowel disease that causes chronic irritation of the colonic mucosa, leading to abdominal pain and bloody diarrhea. Patients are initially treated with medications, however some individuals will have persistent symptoms despite aggressive pharmacologic therapy. Patients with medically refractory fulminant colitis or those who develop toxic megacolon should undergo urgent colectomy. Even with well-controlled symptoms, patients with long-standing ulcerative colitis are at higher risk for developing colorectal cancer. Close endoscopic monitoring is required to detect dysplastic lesions prior to the development of an invasive cancer. A biopsy of high-grade dysplasia should prompt surgery, since a focus of invasive cancer is highly likely. Similar to FAP, the rectal mucosa is at risk for malignancy and must be included in the resection. Total proctocolectomy with ileal pouch—anal anastomosis is the standard operation for this disease.

Colectomy may also be indicated for the treatment of several benign processes. Diverticulosis is a condition wherein outpouchings develop along the wall of the colon, most commonly in the sigmoid region (Fig. 14.3). The incidence of diverticulosis increases with advancing age and may be the result of a low-fiber diet. Asymptomatic diverticulosis does not require any treatment, however two complications can arise from diverticulosis—bleeding or infection. Diverticula occur at the weakest points along the colon—the sites where blood vessels traverse the colonic wall. If one of these diverticula erodes into the adjacent blood vessel, acute lower GI bleeding will result. The hemorrhage associated with diverticulosis may be brisk and life threatening. Endoscopic control of the hemorrhage should be attempted first, but is often not technically possible due to the large amount of blood obscuring visualization. Angiography may be used to localize the precise site of bleeding, and the local delivery of vasopressors or selective embolization may be effective at halting bleeding in some patients. In the presence of exsanguinating hemorrhage from diverticulosis, an emergent colectomy should be performed. Segmental colectomy is acceptable if the source of bleeding has been accurately localized. In most cases, however, the site of bleeding is unknown and a subtotal colectomy should be performed.