Colorectal cancer

Colorectal cancer is quite common. Symptoms of colorectal cancer include blood in the stool or changes in bowel habits. Screening includes stool testing for occult blood. Diagnosis is made by colonoscopy. Treatment of colorectal cancer involves resection and chemotherapy if the lymph nodes are affected.

In the United States, approximately 130,000 cases and 57,000 deaths from colorectal cancer are reported annually. In the Western world, more new cases of colorectal cancer are reported annually than any other cancer except lung cancer. Incidence begins to increase at age 40 and peaks at ages 60–75. Overall, 70% of cases involve the rectum and sigmoid colon and 95% are adenocarcinomas. Colon cancer is more common in women; rectal cancer is more common in men. Synchronous cancers (more than one) occur in 5% of patients.

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What causes colorectal cancer?

Colorectal cancer most often develops as a degeneration of adenomatous polyps. Approximately 80% of cases are sporadic and 20% have a hereditary component. Predisposing factors include chronic ulcerative and granulomatous colitis; the risk of cancer increases with the duration of these diseases.

Populations with high incidence of colorectal cancer consume diets low in fiber and high in animal protein, fat, and refined carbohydrates. Carcinogens may be ingested with food, but are more likely produced by microflora from food, bile, or intestinal secretions. The exact mechanism is unknown.

Colorectal cancer spreads directly through the intestinal wall, hematogenously, by regional metastasis to the lymph nodes, perineurally and by intraluminal metastasis.

Symptoms of colorectal cancer

Colorectal adenocarcinoma grows slowly, and it takes a long time before the first signs may appear. Symptoms depend on the tumor location, type, extent of spread, and complications.

The right colon is large in diameter, thin-walled, and contains fluid, so obstruction is the last to develop. Bleeding is usually hidden. Fatigue and weakness due to severe anemia may be the only complaints. Tumors sometimes become large enough to be palpated through the abdominal wall before other signs appear.

The left colon has a smaller lumen, the stool is of semi-solid consistency, and the tumor tends to narrow the lumen of the intestine circularly, causing transient constipation and increased stool frequency or diarrhea. Clinical symptoms of colorectal cancer are partial obstruction with colicky abdominal pain or intestinal obstruction. The stool may be ribbon-like and mixed with blood. Some patients develop symptoms of perforation, usually with localized (local pain and tension) or less commonly with diffuse peritonitis.

In rectal cancer, the cardinal symptom is bleeding during defecation. Whenever rectal bleeding occurs, even in the presence of significant hemorrhoids or diverticular disease in the anamnesis, concomitant cancer must be excluded. Tenesmus and a sensation of incomplete defecation may be present. Pain occurs when the perirectal tissues are involved.

Some patients may initially present with symptoms and signs of metastatic disease (eg, hepatomegaly, ascites, enlarged supraclavicular lymph nodes).

Screening and diagnosis of colorectal cancer

Screening

Early diagnosis of colorectal cancer depends on routine screening, especially faecal occult blood testing. Cancers detected by this test are usually at an earlier stage and may therefore be more treatable. In patients over 50 years of age with average risk, faecal occult blood testing should be performed annually and flexible sigmoidoscopy every 5 years. Some authors recommend colonoscopy every 10 years instead of sigmoidoscopy. Colonoscopy every 3 years may be more effective. Screening of patients with risk factors (eg, ulcerative colitis) is discussed under the relevant diseases.

Diagnostics

Patients with positive occult blood tests require colonoscopy, as do patients with abnormal findings on barium enema or sigmoidoscopy. All abnormal findings should be completely removed for histologic examination. If the lesion is broad-based or cannot be removed by colonoscopy, surgical treatment should be strongly considered.

Barium enema, especially with double contrast, can detect many pathological changes, but it is not as informative as colonoscopy, so barium enema is less preferable as an initial diagnostic test.

Once cancer is diagnosed, patients should have abdominal CT scan, chest X-ray, and routine laboratory tests to detect metastatic lesions, anemia, and assess homeostasis.

Elevated serum carcinoembryonic antigen (CEAg) levels are seen in 70% of patients with colorectal cancer, but this test is not specific and therefore is not recommended for screening. However, if CEAg levels are high before surgery and low after removal of a colon tumor, CEAg monitoring may be useful for early detection of recurrence. CA 199 and CA 125 are other tumor markers that may also be used.

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Treatment of colorectal cancer

Surgical treatment of colorectal cancer

Surgical treatment of colorectal cancer may be indicated for 70% of patients without signs of metastatic disease. Surgical treatment consists of wide resection of the tumor and its regional lymphatic drainage with anastomosis of the ends of the intestine. If there is 5 cm of unchanged intestine between the tumor lesion and the anal verge, abdominoperineal resection with permanent colostomy is performed.

Resection of a limited number (1-3) of liver metastases is recommended in non-emaciated patients as a subsequent procedure of choice. The criteria are as follows: the primary tumor has been resected, the liver metastasis is confined to one liver lobe, and there are no extrahepatic metastases. Only a small number of patients with liver metastases meet these criteria, but the 5-year survival rate after surgery is 25%.

Colorectal Cancer Stages ¹

Stage	Tumor (maximum invasion)	Metastases to regional lymph nodes	Distant metastases
0	Tis	N0	M0
I	T1 or T2	N0	M0
II	TZ	N0	M0
III	Any Tili T4	Any N or N0
IV	Any T	Any N	M1

¹ TNM classification: Tis - carcinoma in situ; T1 - submucosa; T2 - muscularis propria; T3 - penetrates all layers (for rectal cancer, including perirectal tissue); T4 - adjacent organs or peritoneum.

N0 - no; N1 - 1-3 regional nodes; N2 -> 4 regional nodes; N3 - apical nodes or along the vessels; M0 - no; M1 - present.

Adjuvant treatment for colorectal cancer

Chemotherapy (usually 5-fluorouracil and leucovorin) increases survival by 10-30% in patients with lymph node-positive colon cancer. Combination radiation and chemotherapy is effective in patients with rectal cancer and 1-4 lymph nodes; if more than 4 nodes are affected, combination therapies are less effective. Preoperative radiation and chemotherapy improve resectability of rectal cancer and reduce lymph node metastasis.

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Follow-up screening

In the postoperative period, colonoscopy should be performed annually for 5 years, and then every 3 years if no polyps or tumors are detected. If preoperative colonoscopy was incomplete due to obstructive cancer, a complete colonoscopy should be performed 3 months after surgery.

Additional screening for recurrence should include history, physical examination, and laboratory tests ( complete blood count, liver function tests) every 3 months for 3 years and then every 6 months for 2 years. Imaging studies (CT or MRI) are often recommended for 1 year, but their usefulness is questionable in the absence of abnormalities in screening or blood tests.

Palliative treatment of colorectal cancer

If surgical treatment is not possible or the patient is at high risk for surgery, palliative treatment of colorectal cancer (eg, reduction of obstruction or resection of the perforation zone) is indicated; survival averages 6 months. Some obstructing tumors can be reduced in volume by endoscopic laser photocoagulation, electrocoagulation, or stenting. Chemotherapy can shrink the tumor and prolong survival for several months.

Other drugs have been studied, including irinotecan (Camptosar), oxaliplatin, levamisole, methotrexate, formyltetrahydrofolic acid, celecoxib, thalidomide, and capecitabine (a precursor of 5-fluorouracil). However, there is no single most effective regimen for metastatic colorectal cancer. Chemotherapy for advanced colorectal cancer should be administered by an experienced chemotherapist who has access to drug trials.

If metastasis is limited to the liver, intra-arterial intrahepatic administration of floxuridine or radioactive microspheres using a subcutaneous or external pump attached to a belt is more effective than systemic chemotherapy in an outpatient setting. In case of extrahepatic metastasis, intrahepatic arterial chemotherapy does not offer any advantage over systemic chemotherapy.

What is the prognosis for colorectal cancer?

Colorectal cancer has a different prognosis. It depends on the stage. Ten-year survival rate for cancer limited to the mucous membrane is close to 90%; with growth through the intestinal wall - 70-80%; with damage to the lymph nodes - 30-50%; with metastasis - less than 20%.