Colorectal Tumors

Benign Tumors

Benign colorectal tumors are present in up to 75% of persons > 50 years; the incidence increases with age and peaks in the 7th decade. Most benign tumors are polyps, a clinical term without pathologic significance that refers to any mass of tissue arising from a mucosal surface and protruding into the lumen. Predisposing factors to colorectal polyps are similar to those for colon cancer and include age, diet, geographic distribution, family history, and prior tumors.

Adenomatous polyps, the most common colorectal tumors, are found in 50 to 60% of persons > 60 at autopsy. Lesions may be sessile or pedunculated and, depending on the proportion of the villous component, are classified histologically as tubular, tubulovillous, or villous adenomas. Synchronous lesions (more than one at the same time) occur in about 50% of cases. These polyps are true tumors with malignant potential, which increases with size, proportion of villous elements, and degree of dysplasia. The overall risk of malignant change within an adenomatous polyp is about 1 to 2%.

Other benign lesions include hyperplastic and inflammatory polyps, lipomas, hemangiomas, and leiomyomas. Hyperplastic polyps are common benign tumors. They are small, dome-shaped, sessile lesions with no malignant potential. Patients with inflammatory bowel disorders, ischemic colitis, and certain infections (eg, tuberculosis) are especially prone to developing such polyps. Lipomas, the second most common benign colonic tumor, usually occur at or near the ileocecal valve. Incidence peaks in the 7th to 8th decades. Colonic hemangiomas predominantly occur in elderly patients and are a common cause of hemorrhage. The incidence of leiomyomas seems to peak in the 6th decade and declines sharply thereafter.

Symptoms and Signs

Most polyps are asymptomatic and found incidentally during evaluation for another disorder. Rectal bleeding, usually occult and rarely massive, may occur. Large villous adenomas may cause a severe mucoid rectal discharge and diarrhea, which may eventually result in hypokalemia and hyponatremia. Patients with submucosal tumors (eg, lipomas, hemangiomas, leiomyomas) may present with an abdominal mass or abdominal pain from intussusception.

Diagnosis and Treatment

Polyps are usually detected by barium enema or endoscopy. Air-contrast barium enema is far superior to the single-contrast technique, but endoscopy is the most accurate diagnostic procedure. Total colonoscopy should be performed when an adenomatous polyp > 5 mm is found on sigmoidoscopy because additional polyps in more proximal locations are highly likely. The predictive meaning of polyps < 5 mm is uncertain.

Endoscopic polypectomy is the treatment of choice for adenomatous polyps. Surgical excision may be necessary for submucosal tumors or polyps that cannot be removed endoscopically.

When well-differentiated carcinoma is detected in a polyp and no vascular, lymphatic, or stalk invasion exists and a clear resection margin does exist, the only treatment usually needed is endoscopic polypectomy. If these conditions are not met, surgery may be considered, depending on the location of the adenoma and other factors.

For patients with adenomatous polyps, endoscopic surveillance every 3 to 5 years after polypectomy is recommended.

Malignant Tumors

Colorectal cancer is second only to lung cancer as the most common malignancy among U.S. and Western European men and women. Colorectal cancer is the most common cancer occurring in persons >= 65 years. Although early detection and treatment have improved significantly in the last 2 decades, colorectal cancer continues to be the second leading cause of cancer death. About 130,000 new cases occur annually in the USA, and 57,000 deaths from this disease occur annually. Age is a critical risk factor--incidence begins to increase at age 45 and doubles every 5 years thereafter.

Adenocarcinoma constitutes 95% of all colorectal cancers; others include lymphoma, leiomyosarcoma, and carcinoid tumors. Rectal cancer is slightly more common in men, while colon cancer occurs equally in men and women.

In addition to age, other predisposing factors for colorectal cancer include a family history of colorectal adenomatous polyps or cancer, inflammatory bowel disease, and a family history of colorectal tumors (ie, cancer or an adenomatous polyp diagnosed before age 60). Inherited disorders (eg, familial adenomatous polyposis, hereditary nonpolyposis colorectal cancer) are also associated with a high incidence of colorectal cancer, but they are rarely the cause in the elderly. Some dietary factors (eg, a diet high in animal fat and refined sugar and low in fiber) have been associated with a higher risk of colorectal cancer, but their causative role is controversial.

The extent of tumor spread is graded by a modified Dukes' classification. Dukes' A lesions involve the mucosa; B lesions extend through the wall but do not involve lymph nodes; C lesions involve lymph nodes; and D lesions have distant metastases. Many modifications of this staging system exist.

Symptoms, Signs, and Diagnosis

Colorectal cancer is asymptomatic in its early stages. In later stages, the location of the tumor influences symptoms. Some evidence indicates that elderly patients are more likely to present with right-sided lesions. Synchronous colorectal lesions appear in about 3.5% of patients. Right-sided lesions are usually large, fungating, bleeding masses that cause iron deficiency anemia, fatigue, and weakness. These tumors usually do not cause obstruction but may grow large enough to be palpable on abdominal examination. Left-sided lesions are usually "napkin-ring," obstructive tumors that cause rectal bleeding, crampy abdominal pain, or altered bowel habits because of the narrower caliber of the left colon. Patients with rectal lesions generally present with stool streaked or mixed with blood. They may also complain of tenesmus or a sensation of incomplete evacuation. Palpable lymphadenopathy, hepatomegaly, or both occur only in the late stages.

Diagnosis is made by barium x-ray or endoscopy. Air-contrast barium enema is usually superior to the single-contrast technique. Sigmoidoscopy can detect lesions in the rectum, sigmoid colon, and distal descending colon, the region where about 50% of cancers occur; colonoscopy allows inspection of the entire colon.

Carcinoembryonic antigen (CEA) levels may be elevated in patients with cancer of the colon, pancreas, breast, lung, prostate, stomach, or bladder as well as in those with benign conditions and thus are nonspecific. An elevated CEA level is especially insensitive for early-stage cancers. However, if the CEA level is elevated before surgery and decreases after it, a subsequent rise may indicate a recurrence.

Preoperative staging of colon cancer should include abdominal CT to rule out liver metastases. In rectal tumors, abdominal-pelvic CT is preferred because it allows a more accurate examination of the pelvis. In these cases, chest x-ray helps determine whether pulmonary metastasis has occurred, and endoscopic ultrasound determines the depth of invasion.

Screening

Annual fecal occult blood testing increases detection of colorectal tumors in an early curable stage and improves overall long-term survival. Sigmoidoscopy as a screening technique also seems to improve prognosis. Because of the marked increase in colorectal cancer prevalence with age, the positive predictive value of both strategies increases in older groups.

Prognosis and Treatment

In patients with adenocarcinoma, the 5-year survival rate is about 90% for patients with Dukes' A lesions, 50 to 80% for those with B lesions, 30 to 40% for those with C lesions, and < 5% for those with D lesions.

Surgery is the mainstay of treatment. When possible, comorbid factors (eg, nutritional deficits, cardiovascular decompensation, pulmonary insufficiency) should be corrected as early as possible.

Cancers of the colon and upper rectum preferably are treated by segmental resection and reanastomosis in a single operation. This procedure is extremely safe in elderly patients; the mortality rate for elective surgery is < 10%. In rectal cancer, the use of preoperative radiation therapy, stapling devices, and newer sphincter-preserving surgical techniques permits extirpation of many lesions without the need for permanent colostomy.

Multiple tumors may require subtotal colectomy. However, because low ileorectal anastomoses may lead to severe diarrhea in elderly patients, an adequate amount of large bowel should be left when possible. Preferably, wide excision of the mesentery and regional lymph nodes is performed concurrently.

Cancers of the middle and lower rectum are more problematic surgically in the elderly because abdominoperineal resection with permanent colostomy (the operation most likely to cure) requires lifestyle changes that may be unsatisfactory to some patients. Fortunately, use of a stapling device permits anastomosis lower than is possible with hand-suturing techniques. However, the anal sphincter can be preserved in only about 5% of lower rectal cancers.

About 25% of patients with colorectal cancer develop hepatic metastases. Surgical resection is indicated when fewer than four nodules affect one single lobe and no evidence of extrahepatic spread exists. Major hepatic resection in patients > 70 can be performed with the same postoperative mortality as in younger patients. When surgery is not indicated, hepatic arterial infusion chemotherapy can be used. Compared with systemic treatment, response rates are higher, but overall survival benefit of this procedure is still poor.

Electrocoagulation also may be effective for small lesions. However, according to one study, when it was used for cancers > 4 cm in diameter, the results were poor.

Adjuvant chemotherapy after surgery with 5-fluorouracil-based regimens modulated by levamisole or leucovorin reduces the probability of recurrence and increases survival in patients with Dukes' B2 or C colon cancer. In rectal tumors, chemotherapy and preoperative or postoperative radiation therapy improve local control and long-term survival. Advanced age is not a contraindication for the use of this type of chemotherapy, but monitoring, supportive care, and patient selection are essential. In addition, a reduced-dose schedule is often necessary to minimize complications. No difference in adverse effects between patients younger and older than 65 has been observed in clinical trials.

In many cases, only palliative procedures are possible, either initially or when cancer recurs. A colostomy may help relieve unremitting tenesmus. Radiation therapy can ease the pain of recurrent rectal cancer. Laser therapy has been used to reduce inoperable rectal tumors and prevent obstruction.