Colorectal Cancer the Gastrointestinal Tract Term Paper

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Tobacco use or cigarette smoking is also linked to the development of colorectal cancers most especially after more than 35 years of smoking. but, there is no biological explanation for this link.

Colorectal cancer is often incidentally found in screening procedures and may be completely asymptomatic. But approximately half of patients with colorectal carcinoma experience abdominal pain, this is the most common symptom. About 35% of patients have altered bowel habits, 30% with occult bleeding, and 15% with intestinal obstruction. For right-sided colon cancers, there is a tendency that they are larger and more likely to bleed, whereas left-sided tumors tend to be smaller and more likely to be obstructing.

Presenting symptoms of Colorectal Cancer vary with the anatomic location for the tumor. Stool is generally liquid and passes through the ileocecal valve into the right colon. Cancers arising in the cecum and ascending colon may become quite large but does not result in any obstructive symptoms or noticeable changes of bowel movements. For lesions located in the right colon, it commonly ulcerate and lead to chronic insidious blood loss without alteration in the appearance of the stool. For tumors located at the ascending colon, this often present with symptoms like fatigue, palpitations and sometimes even angina pectoris. They are also found to be accompanied by hyperchromic microcytic anemia indicating iron deficiency. Since stool becomes more concentrated as it passes into the transverse and descending colon, tumors arising in that area tend to impede the passage of stool. This results in the development of abdominal cramping, sometimes obstruction and sometimes even perforation. Radiographically the abdomen of a patient with colorectal carcinoma often reveal a characteristic "napkin-ring" or "apple core" sign which is an annular, constricting lesion. For colorectal cancers arising in the sigmoid area, the condition is often associated with hematochezia, tenesmus and narrowing of the caliber of stool. Anemia is also infrequent in this kind of cancer.

On physical examination, there may be a completely normal finding, particularly those in early stages of the colorectal cancer. General or specific findings due to progression of the disease may also be evident, which include weight loss, cachexia, abdominal discomfort or tenderness, liver mass, abdominal distention, ascites, rectal mass, rectal bleeding, or occult blood on rectal examination.

Staging of Colorectal Cancer and its prognosis for patients is related to the depth of tumor penetration into the bowel wall and the presence of both regional lymph node involvement and distant metastases. A staging system developed by Dukes and applied to a TNM classification method, in which T. stands for the depth of tumor penetration, N represents the presence of lymph node involvement and M. stands for the presence or absence of distant metastases. Dukes a or T1N0M0 numerically represented as I has a pathologic description where cancer is limited to mucosa and submucosa and with an approximate 5-year survival of greater than 90%. Dukes B1 or T2N0M0 numerically represented as I, is when the cancer extends into the muscularis and the patient has an approximate 5-year survival of 85%. Dukes B2 or T3N0M0, numerically represented as II is when the cancer extended into or through the serosa and the patient has an approximate 5-year survival of 70 to 80%. Dukes C. Or TxN1M0 or numerically represented as III is when the cancer involves already the regional lymph nodes and the patient has an approximate 5-year survival of 35 to 65%. And lastly, Dukes D. Or TxNxM1, numerically represented as IV is when there is already distant metastases to the liver, lungs or other organs. The patient in this case has an approximate 5-year survival of only 5%.

Treatment of Colorectal Cancer can either be medical, surgical or both. There have been important advances have regarding the first-line standard therapy of metastatic colorectal cancer. Both a European trial and a U.S. trial found that the rate of response to the combination of 5-FU, leucovorin (LV), and irinotecan (CPT11) was higher than that to 5-FU/leucovorin or CPT11 alone. The higher response rate translated to a greater median survival duration (about 14 mo) with the combination regimen. Studies have also shown that there is an improved response with the addition of oxaliplatin to the 5-FU/leucovorin regimen, while another study reported significantly prolonged progression-free survival with this combination. Anti-VEGF therapy with bevacizumab (Avastin) was shown to increase survival in patients receiving Avastin in combination with irinotecan, 5-FU, and leucovorin.

A clinical trial performed by Herb Hurwirtz and colleagues at Duke University shows that Colorectal cancer was the first cancer type to be responsive to antiangiogenic therapy as demonstrated by the. Standard therapy for metastatic colon cancer is CPT11 plus 5-FU/leucovorin, also known as the Saltz regimen. Another standard therapy was developed for metastatic colorectal cancer in 2005 which is IFL plus bevacizumab (irinotecan, 5-FU, leucovorin, Avastin). Adjuvant chemotherapy is considered for stage II (Dukes B) remains controversial. Patients with Dukes B. disease and any adverse risk factor, those with large primary tumor [T4], pathologic T3 level of invasion >15 mm, left-sided tumor location, obstructing or perforating tumors, <12 lymph nodes removed, poorly differentiated tumors, perineural invasion, venous invasion, elevated tumor markers, tumor budding, tumor nodules.

Surgical procedure for colon cancer is classically the anterior resection. This involves a "no touch" isolation technique. There is a resection margin of 10 cm of grossly normal bowel on both sides of the tumor along with associated lymph nodes is recommended. Although, total colonic resection is performed for patients with familial polyposis and multiple colonic polyps.

Braunwalk, et. al.. "Harrison's Principles of Internal Medicine." 15th ed., McGraw Hill, Vol.1, pg 581-586, 2001.

University of Missouri. "Anatomy and Function of the Gastrointestinal Tract" Health Care, 2008. May 9, 2008

Wafik S. El-Deiry, MD, PhD. "Colon Cancer, Adenocarcinoma," eMedicine, Oct 11, 2006. May 9, 2008"Dennis Lee, MD. "Colon Cancer Screening and Surveillance,"…[continue]

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