5. Colorectal cancer

Colortal cancer is one of the most common Malapin season countered. In fact, it is the third most common cancer, as well as the third leading cause of cancer deaths among both men and women in Canada. In this podcast, we'll discuss the epidemiology of colon cancer, as well as its natural history. Based on that, we'll discuss the rationale for screening programs. Then we'll cover elements on history, physical exam and investigations that can lead to a diagnosis. And finally, we'll discuss staging and treatment. Welcome to surgery 101. The lifetime risk for contracting colorectal cancer in the general population is 6%. The Canadian Cancer Society predicts that 21,500 Canadians will be diagnosed with colorectal cancer in 2008. Approximately 8,900 will die from it. There are a number of factors that increase an individual's risk of developing colorectal cancer. There is a tiny gender difference with men that have very slightly increased risk versus women. Age is a significant risk factor with more than 90% of cases in people over age 50. Pollups are another major risk factor. The natural history of colorectal cancer is described as an adenoma/carcinoma sequence. This means that every cancer arises from an adenomaous polyp in the colon that is undergone a number of well-defined genetic changes, eventually resulting in an invasive cancer. The time it takes to undergo this change is roughly 10 years. Not every polyp undergoes this change, but the greater the number of polyps in the colon, the greater risk there is that one of them will become a cancer. Family history is also an important risk factor. Having a first-degree relative with colorectal cancer confers a 2-3-fold increase in risk. Having a first-degree relative who contracted colorectal cancer at an age under 50 confers a 4-fold increase in risk. There are some hereditary syndromes to be aware of. The most important being hereditary non-polyposis colorectal cancer or HNPCC and familial adenomaous polyposis or FAP. Both of these syndromes are inherited in an autosomal dominant fashion. HNPCC is characterized by formation of polyps with high malignant potential with a rapid progression to cancer at a young age. FAP is characterized by the formation of thousands of polyps in the entire colon. Each polyp has a normal malignant potential, but the fact that there are thousands of polyps means that the affected individual has a 100% risk of developing invasive cancer. Finally, another major risk factor to keep in mind is inflammatory bowel disease. Patients with ulcerative colitis in particular are at risk. In general, 10 years after being diagnosed with ulcerative colitis, there is a 1-2% risk per year of developing a cancer in the colon. Based on this information, we can understand the rationale for the screening strategy for colorectal cancer. As mentioned, in the general population, an adenomaous polyp precedes the appearance of an invasive tumor by roughly 10 years. We also know from studies that the removal of polyps by endoscopy reduces the subsequent appearance of cancer. Finally, if cancer is detected, we know that outcomes are better if tumors are detected and treated early. In 2008, the Alberta Cancer Board released a set of guidelines on colorectal cancer screening. Remember that screening implies that the patient is free of symptoms or signs suggestive of cancer. For an individual of average risk, screening begins at age 50, and the evidence suggests that any one of four approaches is acceptable. First, the patient can undergo serial testing for fecal occult blood every one to two years. A positive result requires a follow-up colonoscopy. Second, the patient can undergo flexible sigmoidoscopy every five years in combination with fecal occult blood testing. If either the sigmoidoscopy or occult blood testing is abnormal, a follow-up colonoscopy is required. This is true even if the sigmoidoscopy detects polyps or a tumor because the remainder of the colon will need to be evaluated. The third option is for a double contrast barrier minima every five years. An adenoma result requires a follow-up colonoscopy. Finally, a fourth screening option is for complete colonoscopy every 10 years. There are separate screening recommendations for moderate or high-risk individuals. With colorectal cancer is not detected on screening, it can present clinically in a number of different ways. Signs and symptoms depend on what part of the colon the tumor is in. Right-sided tumors tend to present in an insidious manner. Because of the location, gross blood in the stool is unusual. Plus, stool is of a liquid consistency in the right colon, so a tumor can grow quite large before any obstructive symptoms are noted. In general, patients may complain of fatigue, anorexia, or weight loss. Sometimes there is abdominal discomfort, and advanced tumors may present as a palpable mass. Lab studies may reveal anemia. As a general rule of thumb, a macrositic anemia in an adult male or a postmenopausal female is colon cancer until proven otherwise. left-sided tumors present differently. They may actually be some gross blood seen in the stool, depending on how much the tumor is pleating, and how distal it is. The stool in the left colon is more solid, and therefore alterations and bowel habits become the predominant symptoms. The patient may describe passing pencil-thin stools. They may have noticed worsening constipation, or alternating constipation in diarrhea. In some cases, the patient's first presentation is with a distal large bowel obstruction. For rectal cancers, the primary symptom is usually gross pleating per rectum. The patient may also notice mucus discharge, a change in bowel habits, or even a feeling of fullness, or incomplete emptying in the rectum. Patients presenting with signs and symptoms suspicious for colorectal cancer should have a complete physical exam, focusing on the abdomen. Palpate the abdomen and make note of any masses in all four quadrants. Check for jaundice and palpable liver masses since the liver is in most common sight for metastatic colorectal cancer. Every patient must have a digital rectal exam. A significant number of rectal cancers are actually palpable on digital exam. As mentioned, it is important to order a complete blood count. An adult male or postmenopausal female with macrositic anemia has colon cancer until proven otherwise. The most critical step in for the workup of a positive finding on screening test, or concerning history, physical exam, or live findings, is the colonoscopy. Colonoscopy allows for a detailed examination of the entire colon and rectum from the anus to the aliceical valve. While there are non-invasive ways of doing this, including barium NMI and CT colonoscopy, neither of these modalities allows biopsy or polypectomy to be done, if an abnormality is found. In the event that a cancer is found in the colon, the patient must undergo staging investigations. Again, even if a mass was found on flexible sigmoidoscopy, biopsied and proven to be cancer, a full colonoscopy is still needed for proper staging. This is because up to 5% of the time, there is another cancer present in the colon. This is referred to as a synchronous lesion. Further staging investigations include a CT scan of the abdomen and a chest x-ray or CT scan of the chest. In addition to routine preoperative blood work, blood tests checking for the level of the tumor marker, CEA, or carcinnoembryonic antigen should be ordered. CEA levels can't be used for diagnostic purposes, but a pre-treatment CEA level can help for interpretation of post-treatment CEA levels with regards to monitoring for occurrence. Colorectal cancer staging is done using the TNM or tumor nodes metastasis system. Preoperative staging gives a rough idea of the T-stage and a good idea of the M-stage. The N-stage requires examination of the surgical specimen. Regardless of stage, surgical resection of the tumor is almost always part of the treatment for colorectal cancer. This is true even if the disease is metastatic at the time of diagnosis. There are two reasons for this. First, resection of the tumor prevents bowel obstruction and ongoing bleeding, which is an important paliating measure. Second, in select patients with liver and lung metastasis, resection of the primary tumor followed by resection of the metastasis can be attempted with the goal of actually curing the disease. These situations are not common, and the decision to proceed along this line of treatment has to be made by a multidisciplinary tumor group. Colon resections for cancer involve removing the involved segment of colon along with this lymphovascular tree. Right hemiclelectomy, left hemiclelectomy, and sigmoidectomy are commonly performed operations for colon cancers. In general, the tumor is identified, and then the colon is mobilized to allow for resection of the affected segment along with its blood supply, followed by re-enastomosis of the free ends of the bowel. The mobilization involves freeing the colon from its retroperitomial attachments, as well as taking down the hepatic flexure for right hemiclelectamines, and the splenic flexure for left hemiclelectamines. In rectal cancer, the procedure done depends on the distance of the tumor from the anal sphincter complex. Ideally, a 2 cm margin is desired distal to the tumor. If this margin can be obtained, a swing to preserving. Low in. interior resection can be done. The name of the procedure comes from the fact that the procedure is done entirely from an interior trans-abdominal approach. No dissection is done from the perineum, and the sphincters are preserved. A special stapling device is introduced through the anus to allow for re-enastomosis of the bowel. If the two centimeter margin can't be obtained, with the tumor obviously involves the sphincter complex, a proper resection can't be done without sacrificing the sphincters. This is one of the procedure known as an abdominal perineal resection, or APR is used. The name reflects the fact that the procedure involves both an abdominal and perineal approach to the resection. The APR removes the entire rectum and anus and leaves the patient with a permanent colostomy. Radiation does not play a role in colon cancer treatment, but it is becoming increasingly important in rectal cancer treatment. The details are still a matter of debate, but it is enough to know that many patients do better if they receive radiation prior to surgery for the rectal cancers. Chemotherapies offered postoperatively to patients with no positive disease or metastases. Patients without nodal or distant meds may also receive chemotherapy depending on the characteristics of the primary tumor. Following surgery for cure, a patient requires close follow-up. Most recurrences are seen within two years of the resection, and therefore follow-up investigations and most frequent surgery during that time. This concludes our very brief discussion of colorectal cancer. Key points to remember include 1. Colorectal cancer is common and deadly. It is the third most common cancer and the third most common cause of cancer death in Canada. 2. Colorectal cancer develops in a well-characterized sequence, wherein an adenovitis polyp undergoes transformation to an invasive cancer over a period of roughly ten years of the average risk individual. 3. The frequency of colorectal cancer, along with the long pre-cancer stage, combined with the excellent outcomes that can be seen with treatment of early cancers are the rationale behind screening for the disease. 4. Symptoms are different depending on the location of the tumor. Right-sided tumors are more insidious. Left-sided tumors result in alterations in bowel habit. Rectol tumors present with bleeding. Remember that macrosidic anemia in an adult male or post-menopausal female indicate the presence of colorectal cancer until proven otherwise. 5. Surgery is the mainstay of treatment. Colorectal tumors are resected, along with a continuous segment of colon, and the associated lymphobascular supply. Rectol cancers are treated with low anterior resection, if they are more than two centimeters from the anal sphincter. More by abdominal perineal resection, if they are less than two centimeters from the sphincter. As well, radiation therapy is becoming increasingly important in the treatment of rectal cancers.