- Cancer Definition
- Colon Definition
- Colon Cancer Definition
- Risk Factors & Causes
- Symptoms & Signs
- Survival Rates
- Follow-up Care
What is cancer?
Every day within our bodies, a massive process of destruction and repair occurs. The human body is comprised of about 15 trillion cells, and every day billions of cells wear out or are destroyed. In most cases, each time a cell is destroyed the body makes a new cell to replace it, trying to make a cell that is a perfect copy of the cell that was destroyed because the replacement cell must be capable of performing the same function as the destroyed cell. During the complex process of replacing cells, many errors occur. Despite remarkably elegant systems in place to prevent errors, the body still makes tens of thousands of mistakes daily while replacing cells either because of random errors or because there are outside pressures placed on the replacement process that promote errors. Most of these mistakes are corrected by additional elegant systems or the mistake leads to the death of the newly made cell, and another normal new cell is produced. Sometimes a mistake is made, however, and is not corrected. Many uncorrected mistakes have little effect on health, but if the mistake allows the newly made cell to divide independent of the checks and balances that control normal cell growth, that cell can begin to multiply in an uncontrolled manner. When this happens, a tumor (essentially a mass of abnormal cells) can develop.
Tumors fall into two categories: there are benign (noncancerous) tumors and malignant (cancerous) tumors. So what is the difference? The answer is that a benign tumor grows only in the tissue from which it arises. Benign tumors sometimes can grow quite large or rapidly and cause severe symptoms, even death, although most do not. For example, a fibroid tumor in a woman's uterus is a type of benign tumor. It can cause bleeding or pain, but it will never travel outside the uterus and grow as a new tumor elsewhere. Fibroids, like all benign tumors, lack the capacity to shed cells into the blood and lymphatic system, so they are unable to travel to other places in the body and grow. Cancer, on the other hand, can shed cells that can travel through the blood or lymphatic system, landing in tissues distant from the primary tumor and growing into new tumors in these distant tissues. This process of spreading to distant tissues, called metastasis, is the defining characteristic of a cancerous or malignant tumor.
Benign tumor cells often look relatively normal in appearance when examined under the microscope. Malignant or cancerous cells usually look more abnormal in appearance when similarly viewed under the microscope.
Cancer is a group of more than 100 different diseases, much like infectious diseases. Cancers are named by the tissues from which the first tumor arises. Hence, a lung cancer that travels to the liver is not a liver cancer but is described as lung cancer metastatic to the liver, and breast cancer that spreads to the brain is not described as a brain tumor but rather as breast cancer metastatic to the brain. Each cancer is a different disease with different treatment options and varying prognoses (likely outcomes or life expectancy). In fact, each individual with cancer has a unique disease, and the relative success or lack thereof of treatment among patients with the same diagnosis may be very different. As a result, it is important to treat each person with a diagnosis of cancer as an individual regardless of the type of cancer.
What is the colon and what does it do?
The colon and the rectum are the final portions of the tube that extends from the mouth to the anus. Food enters the mouth where it is chewed and then swallowed. It then travels through the esophagus and into the stomach. In the stomach, the food is ground into smaller particles and then enters the small intestine in a carefully controlled manner. In the small intestine, the final digestion of food and absorption of the nutrients contained in the food occurs. The food that is not digested and absorbed enters the large intestine (colon) and finally the rectum. The large intestine acts primarily as a storage facility for waste; however, additional water, salts, and some vitamins are further removed. In addition, some of the undigested food, for example, fiber, is digested by colonic bacteria and some of the products of digestion are absorbed from the colon and into the body. (It is estimated that 10% of the energy derived from food comes from these products of bacterial digestion in the colon.) The remaining undigested food, dying cells from the lining of the intestines, and large numbers of bacteria are stored in the colon and then periodically passed into the rectum. Their arrival into the rectum initiates a bowel movement that empties the colonic contents from the body as stool.
Although the large intestine is a tube, it is structurally a complicated tube, more like a steel-belted radial tire than a garden hose. The tube is comprised of four layers. The first is an inner layer of cells that line the cavity through which the undigested and digesting food travels, called the mucosa. The mucosa is attached to a thin second layer, the submucosa, that is attached itself to a layer of muscle, the muscularis. The entire tube is surrounded by fibrous (scar-like) tissue called the serosa. The most common cancers of the large intestine (the type called adenocarcinoma) arise from the mucosa, the inner layer of cells. These cells are exposed to toxins from food and bacteria as well as mechanical wear and tear, and they are relatively turning over rapidly (dying off and being replaced). Mistakes (usually a series of mistakes involving genes within the replacement cells) lead to abnormal cells and uncontrolled proliferation of the abnormal cells that give rise to cancer. The rapid turnover allows for more mistakes to occur as compared with tissues that do not turn over so rapidly (for example, liver tissue).
How long is the human colon?
The human large intestine (colon) is about 6 feet long.
Where is the colon located?
Most of the large intestine rests inside a cavity in the abdomen called the peritoneal cavity. Parts of the colon are able to move quite freely within the peritoneal cavity as the undigested food is passing through it. As the colon heads towards the rectum, it becomes fixed to the tissues behind the peritoneal cavity, an area called the retroperitoneum. The end portion of the large intestine, the part that resides in the retroperitoneum, is the rectum. Unlike much of the rest of the colon, the rectum is fixed in place by the tissues that surround it. Because of its location, treatment for rectal cancer often is different than treatment for cancer of the rest of the colon.
What is colorectal cancer?
Cancers of the colon and rectum (colorectal cancer) start when the process of the normal replacement of colon lining cells goes awry. Mistakes in cell division occur frequently. For reasons that are poorly understood, sometimes mistakes occur that escape our editing systems. When this occurs, these cells begin to divide independently of the normal checks and balances that control growth. As these abnormal cells grow and divide, they can lead to growths within the colon called polyps. Polyps vary in type, but many are precancerous tumors that grow slowly over the course of years and do not spread. As polyps grow, additional genetic mutations further destabilize the cells. When these precancerous tumors change direction (growing into the wall of the tube rather than into the space in the middle of it) and invade other layers of the large intestine (such as the submucosa or muscular layer), the precancerous polyp has become cancerous. In most cases this process is slow, taking at least eight to 10 years to develop from those early aberrant cells to a frank cancer. Colorectal cancer is typically an adenocarcinoma, a term that refers to a cancer that has formed in certain types of lining tissues in the body.
Once a colorectal cancer forms, it begins to grow in two ways. First, the cancer can grow locally and extend through the wall of the intestine and invade adjacent structures, making the mass (called the primary tumor) more of a problem and harder to remove. Local extension can cause additional symptoms such as pain or fullness, perforation of the colon, or blockages of the colon or nearby structures. Second, as the cancer grows it begins the process of metastasis, shedding thousands of cells a day into the blood and lymphatic system that can cause cancers to form in distant locations. Colorectal cancers most commonly spread first to local lymph nodes before traveling to distant organs. Once local lymph nodes are involved, spread to the liver, the abdominal cavity, and the lung are the next most common destinations of metastatic spread.
Colorectal cancer is the third most common cause of cancer in the U.S. in both men and women. It affects over 135,000 people annually, representing 8% of all cancers. About 4.3% of people will be diagnosed with colon or rectum cancer at some point in their lives.
What are colon cancer risk factors and causes?
Health care professionals are certain that colorectal cancer is not contagious (a person cannot catch the disease from a cancer patient). Some people are more likely to develop colorectal cancer than others. Factors that increase a person's risk of colorectal cancer include increasing age, African-American race, high fat intake, a family history of colorectal cancer and polyps, the presence of polyps in the large intestine, and inflammatory bowel diseases, primarily chronic ulcerative colitis.
Increasing age is the main risk factor for colorectal cancer. Around 90% of colorectal cancers are diagnosed after age 50.
African Americans have a higher incidence of colorectal cancer than people of other races.
Diet and colorectal cancer
Diets high in fat have been shown in numerous research studies to predispose people to colorectal cancer. In countries with high colorectal cancer rates, the fat intake by the population is much higher than in countries with low cancer rates. It is believed that the digestion of fat that occurs in the small intestine and the colon leads to the formation of cancer-causing chemicals (carcinogens). Likewise, research studies also reveal that diets high in vegetables and high-fiber foods such as whole-grain breads and cereals contain less fat that produces these carcinogens and may counter the effects of the carcinogens. Both effects would help reduce the risk of cancer.
Colon polyps and colorectal cancer
Research has shown that most colorectal cancers develop in colorectal polyps. Therefore, removing benign (but precancerous) colorectal polyps can prevent colorectal cancer. Precancerous colorectal polyps are most commonly called adenomatous polyps. They develop when chromosomal damage occurs in cells of the inner lining of the colon. The damage produces abnormal cells, but the cells have not yet developed the ability to spread, the hallmark of cancer. Instead, the growing tissue remains localized within the polyp. When chromosomal damage increases further within the polyp, cell growth becomes uncontrolled, and the cells begin to spread, that is, they become cancer. Thus, colon polyps which are initially benign acquire additional chromosome damage to become cancerous.
Ulcerative colitis and colorectal cancer
Chronic ulcerative colitis causes inflammation of the inner lining of the colon. Bowel cancer is a recognized complication of chronic ulcerative colitis. The risk for cancer begins to increase after eight to 10 years of colitis. The risk of developing colon cancer in a patient with ulcerative colitis also is related to the location and the extent of his or her disease.
Patients at higher risk of cancer are those with a family history of colon cancer, a long duration of ulcerative colitis, extensive colon involvement with ulcerative colitis, and those with ulcerative colitis-associated liver disease, sclerosing cholangitis.
Since the cancers associated with ulcerative colitis have a more favorable outcome when caught at an earlier stage, yearly examinations of the colon often are recommended after eight years of known extensive disease. During these examinations, samples of tissue (biopsies) are taken to search for precancerous changes in the cells lining the colon. When precancerous changes are found, removal of the entire colon may be necessary to prevent colon cancer.
Genetics and colorectal cancer
A person's genetic background is an important factor in colon cancer risk. Having a first-degree relative with colorectal cancer, especially if the cancer was diagnosed before the age of 55 years, roughly doubles the risk of developing the condition.
Even though a family history of colon cancer is an important risk factor, a majority (80%) of colon cancers occur sporadically in patients with no family history of colon cancer. Approximately 20% of cancers are associated with a family history of colon cancer.
Chromosomes contain genetic information, and chromosomal damage causes genetic defects that lead to the formation of colon polyps and later colon cancer. In sporadic polyps and cancers (polyps and cancers that develop in the absence of family history), the chromosome damages are acquired (develop in a cell during adult life). The damaged chromosomes can only be found in the polyps and the cancers that develop from that cell. But in hereditary colon cancer syndromes, the chromosomal defects are inherited at birth and are present in every cell in the body. Patients who have inherited the hereditary colon cancer syndrome genes are at risk of developing colon polyps, usually at young ages, and are at very high risk of developing colon cancer early in life; they also are at risk of developing cancers in other organs.
Familial adenomatous polyposis (FAP) is one hereditary colorectal cancer syndrome where the affected family members will develop countless numbers (hundreds, sometimes thousands) of colon polyps starting during their teens. Unless the condition is detected and treated early (treatment involves removal of the colon), a person affected by FAP is almost sure to develop colon cancer from these polyps. Cancers almost certainly develop by the time a person is in their 40s. These patients are also at risk of developing other cancers such as cancers in the thyroid gland, stomach, and the ampulla (part of the bile duct where it drains into the small intestine from the liver) as well as benign tumors called desmoid tumors. FAP arises from a mutation in a specific gene called the APC gene. The specific mutation can be identified in most people with appropriate testing, and such testing is recommended for individuals diagnosed with FAP as well as their family members.
Attenuated familial adenomatous polyposis (AFAP) is a milder version of FAP. Affected members develop fewer than 100 colon polyps. Nevertheless, they are still at very high risk of developing colon cancers at a young age. They are also at risk of having gastric polyps and duodenal polyps.
Hereditary non-polyposis colon cancer (also known as Lynch syndrome or HNPCC) is a hereditary colorectal cancer syndrome where affected family members can develop colon polyps and cancers, usually in the right colon, in their 30s to 40s. Patients with HNPCC are also at risk of developing uterine cancer, stomach cancer, ovarian cancer, and cancers of the ureters (the tubes that connect the kidneys to the bladder), and the bile ducts. Ironically, it appears that while colon cancer occurs more frequently in patients with HNPCC, these cancers may be more easily cured than "sporadic" colon cancers. The specific genetic abnormalities associated with HNPCC have been identified, and patients and family members can be tested to determine if HNPCC is present and if family members carry the abnormality and are likely to develop cancer.
MYH polyposis syndrome is a recently discovered hereditary colorectal cancer syndrome. Affected members typically develop 10 to 100 polyps at around 40 years of age and are at high risk of developing colon cancer. Here, too, the genetic abnormality has been identified.
It is important to remember that the overwhelming majority of colorectal cancers do not have a single, identifiable chromosomal abnormality that can be looked for in relatives in order to identify individuals at risk for colorectal cancer.
What are the symptoms and signs of colon cancer?
Colorectal cancer-related symptoms are numerous and nonspecific. They include
- shortness of breath,
- change in bowel habits,
- narrow stools,
- diarrhea or constipation,
- red or dark blood in stool,
- weight loss,
- abdominal pain,
- cramps, or
Colorectal cancer can be present for several years before symptoms develop. Symptoms vary according to where in the large intestine the tumor is located. The right colon is wider and more flexible. It can even be called relatively spacious as compared to the rest of the colon. Cancers of the right colon can grow to large sizes before they cause any abdominal symptoms.
- Typically, right-sided cancers cause iron deficiency anemia due to the slow loss of blood over a long period of time. Iron deficiency anemia causes fatigue, weakness, and shortness of breath.
- The left colon is narrower than the right colon. Therefore, cancers of the left colon are more likely to cause partial or complete bowel obstruction.
Cancers causing partial bowel obstruction can cause symptoms of
How is colon cancer diagnosed?
When colon cancer is suspected, a colonoscopy is typically performed to confirm the diagnosis and locate the tumor.
Colonoscopy is a procedure whereby a health care professional inserts a long, flexible viewing tube into the rectum for the purpose of inspecting the inside of the entire colon. Colonoscopy is generally considered more accurate than barium enema X-rays, especially in detecting small polyps. If colon polyps are found, they usually are removed through the colonoscope and sent to the pathologist. The pathologist examines the polyps under the microscope to check for cancer. Colonoscopy is the best procedure to use when cancer of the colon is suspected. While the majority of the polyps removed through colonoscopes are benign, many are precancerous. Removal of precancerous polyps prevents the future development of colon cancer from these polyps.
Sigmoidoscopy is a procedure performed using a shorter flexible scope to examine just the left colon and rectum. It is more easily prepared for and performed than a complete colonoscopy but has obvious limitations in terms of not being long enough to assess both the right and transverse colons. Polyp removal and cancer biopsy can be performed through the sigmoidoscope.
If cancerous growths are found during colonoscopy, small tissue samples (biopsies) can be obtained and examined under the microscope to determine if the polyp is cancerous. If colon cancer is confirmed by a biopsy, staging examinations are performed to determine whether cancer has already spread to other organs. Since colorectal cancer tends to spread to the lungs and the liver, staging tests usually include CT scans of the lungs, liver, and abdomen. Positron emission tomography (PET) scans, a newer test that looks for the increased metabolic activity that is common in cancerous tissue, also are employed frequently to look for the spread of colon cancer to lymph nodes or other organs.
Sometimes, the health care professional may obtain a "tumor marker" blood test called a carcinoembryonic antigen (CEA) if there is a suspicion of cancer. CEA is a substance produced by some colon and rectal cancer cells as well as by some other types of cancers. It is sometimes found in high levels in patients with colorectal cancer, especially when the disease has spread. It can serve as a useful test to follow if it is found to be elevated before the cancer is removed. However, not all patients with colorectal cancer will have an elevated CEA even if their cancer has spread. (Some colorectal cancers don't produce it.) Additionally, some patients without cancer can have an elevated CEA blood test. About 15% of smokers, for example, will have an elevated CEA without colon cancer. So the CEA is not used to diagnose colorectal cancer but rather to follow the effects of treatment of colorectal cancer in someone with a known history of the disease because, again, in some patients, the amount of cancerous tissue correlates with the level of CEA.
What are the stages of colon cancer?
When colorectal cancer is diagnosed, additional tests are performed to determine the extent of the disease. This process is called staging. Staging determines how advanced colorectal cancer has become. The staging for colorectal cancer ranges from stage I, the least advanced cancer, to stage IV, the most advanced cancer.
- Stage I colorectal cancers involve only the innermost layers of the colon or rectum. The likelihood of cure (excellent prognosis) for stage I colorectal cancer is over 90%.
- Stage II cancers exhibit greater growth and extension of the tumor through the wall of the colon or rectum into adjacent structures.
- Stage III colorectal cancers manifest the spread of cancer to local lymph nodes.
- Stage IV (metastatic) colorectal cancers have spread or metastasized, to distant organs or lymph nodes far from the original tumor.
With each subsequent stage of colon cancer, the risk for recurrent cancer and death due to the spread of cancer (metastasis) rises. As noted, earlier cancers have lower risks of recurrence and death. By the time an individual has stage IV colorectal cancer, the prognosis is poor. However, even in stage IV colorectal cancer (depending on where cancer has spread), the opportunity for a cure exists.
What are colon cancer survival rates?
Survival rates for any cancer are often reported by stage and the extent of spread when the cancer is identified.
- For colon and rectum cancer, around 39% are diagnosed at the local stage, before cancer has spread outside the local area.
- The five-year survival for these patients with localized colon and rectum cancer is around 90%.
When cancer has spread to the regional lymph nodes near the site of origin, the five-year survival rate is about 72%. When cancer has metastasized to distant sites in the body (stage IV cancer), the five-year survival rate lowers to about 14%.
5-year relative survival rates for colon cancer based on people diagnosed with cancers of the colon between the year 2011 and 2017 is shown in the below chart.
|SEER stage||The 5-year relative survival rate|
|All SEER stages combined||64%|
*SEER = Surveillance, Epidemiology, and End Results
What is the treatment for colon cancer?
Surgery is the most common initial medical treatment for colorectal cancer. During surgery, the tumor, a small margin of the surrounding healthy intestine, and adjacent lymph nodes are removed. The surgeon then reconnects the healthy sections of the bowel. In patients with rectal cancer, the rectum sometimes is permanently removed if cancer arises too low in the rectum. The surgeon then creates an opening (colostomy) on the abdominal wall through which solid waste from the colon is excreted. Specially trained nurses (enterostomal therapists) can help patients adjust to colostomies, and most patients with colostomies return to a normal lifestyle.
For early bowel cancers, the recommended treatment is surgical removal. For most people with early-stage colon cancer (stage I and most stage II), surgery alone is the only treatment required. Chemotherapy may be offered to some people with stage II cancers who have factors suggesting that their tumor may be at higher risk of recurrence. However, once colon cancer has spread to local lymph nodes (stage III), the risk of the cancer returning remains high even if all visible evidence of cancer has been removed by the surgeon. This is due to an increased likelihood that tiny cancer cells may have escaped prior to surgery and are too small to detect at that time by blood tests, scans, or even direct examination. Their presence is deduced from a higher risk of recurrence of colon cancer at a later date (relapse). Oncologists recommend additional colon cancer treatments with chemotherapy in this setting to lower the risk of cancer's return.
Drugs used for chemotherapy enter the bloodstream and attack any colon cancer cells that were shed into the blood or lymphatic systems prior to the operation, attempting to kill them before they set up shop in other organs. This strategy, called adjuvant chemotherapy, has been proven to lower the risk of cancer recurrence and is recommended for all patients with stage III colon cancer who are healthy enough to undergo it, as well as for some higher-risk stage II patients whose tumor may have been found to have obstructed or perforated the bowel wall prior to surgery.
There are several different options for adjuvant chemotherapy for the treatment of colon cancer. The treatments involve a combination of chemotherapy drugs given orally or into the veins. The treatments typically are given for a total of six months. It is important to meet with an oncologist who can explain adjuvant chemotherapy options as well as side effects to watch out for so that the right choice can be made for a patient as an individual.
Chemotherapy usually is given in a health care professional's clinic, in the hospital as an outpatient, or at home. Chemotherapy usually is given in cycles of treatment followed by recovery periods without treatment. Side effects of chemotherapy vary from person to person and also depend on the agents given. Modern chemotherapy agents are usually well-tolerated and side effects for most people are manageable. In general, anticancer medications destroy cells that are rapidly growing and dividing. Therefore, normal red blood cells, platelets, and white blood cells that also are growing rapidly can be affected by chemotherapy. As a result, common side effects include anemia, loss of energy, and low resistance to infections. Cells in the hair roots and intestines also divide rapidly. Therefore, chemotherapy can cause hair loss, mouth sores, nausea, vomiting, and diarrhea, but these effects are transient.
Treatment of stage IV colorectal cancer
Once colorectal cancer has spread distantly from the primary tumor site, it is described as stage IV disease. These distant tumor deposits, shed from the primary tumor, have traveled through the blood or lymphatic system, forming new tumors in other organs. At that point, colorectal cancer is no longer a local problem but is instead a systemic problem with cancer cells both visible on scan and undetectable, but likely present elsewhere throughout the body. As a result, in most cases, the best treatment is chemotherapy, which is a systemic therapy. Chemotherapy in metastatic colorectal cancer has been proven to extend life and improve the quality of life. If managed well, the side effects of chemotherapy are typically far less than the side effects of uncontrolled cancer. Chemotherapy alone cannot cure metastatic colon cancer, but it can more than double life expectancy and allow for good quality of life during the time of treatment.
Chemotherapy options for colorectal cancer treatment vary depending on other health issues that an individual faces. For fitter individuals, combinations of several chemotherapeutic drugs usually are recommended, whereas, for sicker people, simpler treatments may be best. Different multidrug regimens combine agents with proven activity in colorectal cancer such as 5-fluorouracil (5-FU), which is often given with the drug leucovorin (also called folinic acid) or a similar drug called levoleucovorin, which helps it work better.
Capecitabine is a chemotherapy drug given in pill form. Once in the body, it is changed to 5-FU when it gets to the tumor site. Other chemotherapy drugs for colorectal cancer are irinotecan, oxaliplatin, and trifluridine and tipiracil, a combination drug in pill form. Chemotherapy regimens often have acronyms to simplify their nomenclature (such as FOLFOX, FOLFIRI, and FLOX).
Targeted therapies are newer treatments that target specific aspects of the cancer cell, which may be more important to the tumor than the surrounding tissues, offering potentially effective treatments with fewer side effects than traditional chemotherapy. Bevacizumab, cetuximab, panitumumab, ramucirumab, regorafenib, and ziv-aflibercept are targeted therapies that have been used in the management of advanced colorectal cancer. These newer chemotherapeutic agents most often are combined with standard chemotherapy to enhance their effectiveness.
If the first treatment is not effective, second and third options are available that can confer a benefit to people living with colorectal cancer.
Radiation therapy is the primary treatment of colorectal cancer and has been limited to treating cancer of the rectum. As noted earlier, whereas parts of the colon move freely within the abdominal cavity, the rectum is fixed in place within the pelvis. It is in an intimate relationship with many other structures and the pelvis is a more confined space. For these reasons, a tumor in the rectum often is harder to remove surgically because space is smaller and other structures can be involved with cancer. As a result, for all but the earliest rectal cancers, initial chemotherapy and radiation treatments (a local treatment to a defined area) are recommended to try and shrink cancer, allowing for easier removal and lowering the risk of cancer returning locally. Radiation therapy is typically given under the guidance of a radiation oncologist. Initially, individuals undergo a planning session, a complicated visit as the doctors and technicians determine exactly where to give the radiation and which structures to avoid. Chemotherapy usually is administered daily while the radiation is delivered. Side effects of radiation treatment include fatigue, temporary or permanent pelvic hair loss, and skin irritation in the treated areas.
Radiation therapy will occasionally be used as a palliative treatment to reduce pain from recurrent or metastatic colon or rectal cancer.
What is the follow-up care for colon cancer?
Follow-up exams are important for people with colorectal cancer. The cancer can come back near the original site, although this is unusual. If the cancer returns, it typically does so in a distant location such as the lymph nodes, liver, or lungs. Individuals diagnosed with colorectal cancer remain at risk of their cancer returning for up to 10 years after their original diagnosis and treatment, although the risk of recurrence is much higher in the first few years. Medical providers in the United States follow patients with physical examinations and blood tests including the CEA (if it was elevated before surgery) tumor marker every three months for the first two years and then with decreasing frequency thereafter. Patients are also followed with colonoscopies (starting one year after their diagnosis) and with CT scans (typically performed at least once yearly for the first two to five years).
If a recurrence is noted either locally or with metastatic spread, individuals may still be treated with the intention of cure. For example, if a new tumor were to recur in the liver, individuals can be treated with a combination of chemotherapy and surgery (or sophisticated radiation techniques) in hopes of eradicating the cancer completely. Evaluation in hospitals of excellence that specialize in liver surgery can help guide these complicated treatment decisions and increase the chances of cure even in the setting of metastatic disease.
In addition to checking for cancer recurrence, patients who have had bowel cancer may have an increased risk of cancer of the prostate, breast, and ovary. Therefore, follow-up examinations in the clinic should include cancer screening for these diseases, as well.
What is the prognosis for patients with colorectal cancer?
Colorectal cancers are typically slow-growing cancers that take years to develop. Because they grow most often in a step-wise manner, screening can greatly reduce the likelihood of death associated with the disease. Whether with virtual colonoscopy or newer screening techniques, the future must focus first and foremost on better, more comprehensive screening programs that find polyps and early cancers before they become life-threatening. The public also must be educated on the value of screening programs.
For those living with cancer, intensive research is ongoing to better understand cancer biology and genetics so that specific approaches can be developed to attack specific types of cancers and, more importantly, specific individuals' cancers. Each person living with cancer has a disease with a unique biology and genetic code and the secret to better treatments involves unlocking that code. Cancer is very complex and scientists are just beginning to unravel its secrets. Progress is frustratingly slow for those battling the disease. With each passing year, however, our understanding increases and treatments become more refined. If you or your family member is living with colorectal cancer, speak with your doctor about ways you can participate in research through clinical trials to help increase our knowledge and improve our therapies for this difficult disease.
Is it possible to prevent colon cancer?
The most effective prevention for colorectal cancer is early detection and removal of precancerous colorectal polyps before they turn cancerous. Even in cases where cancer has already developed, early detection still significantly improves the chances of a cure by surgically removing cancer before the disease spreads to other organs.
Regular physical activity is associated with a lower risk of colon cancer. Aspirin use also appears to lower the risk of bowel cancer. The use of combined estrogen and progestin in hormone replacement therapy lowers the risk of colon cancer in postmenopausal women. Hormone replacement therapy has risks that must be weighed against this effect and should be discussed with a doctor.
Genetic counseling and testing
Blood tests are now available to test for hereditary colon cancer syndromes. Families with multiple members having colon cancers, multiple colon polyps, cancers at young ages, and other cancers such as cancers of the ureters, uterus, duodenum, and more, may take advantage of resources such as genetic counseling, followed possibly by genetic testing. Genetic testing without prior counseling is discouraged because of the extensive family education that is involved and the complicated nature of interpreting the test results.
The advantages of genetic counseling followed by genetic testing include (1) identifying family members at high risk of developing colon cancer to begin colonoscopies early; (2) identifying high-risk members so that screening may begin to prevent other cancers such as ultrasound tests for uterine cancer, urine examinations for ureter cancer, and upper endoscopies for stomach and duodenal cancers; and (3) alleviating concern for members who test negative for the hereditary genetic defects.
Diet to prevent colon cancer
People can change their eating habits by reducing fat intake and increasing fiber (roughage) in their diet. Major sources of fat are meat, eggs, dairy products, salad dressings, and oils used in cooking. Fiber is the insoluble, nondigestible part of plant material present in fruits, vegetables, and whole-grain bread and cereals. It is postulated that high fiber in the diet leads to the creation of bulky stools which can rid the intestines of potential carcinogens. In addition, fiber leads to the more rapid transit of fecal material through the intestine, thus allowing less time for a potential carcinogen to react with the intestinal lining.
Screening for colorectal cancer
The term "screening" is properly applied only to the use of testing to look for evidence of cancer or pre-cancerous polyps in individuals who are asymptomatic and at only average risk for a type of cancer. Those patients who, for example, have a positive family history of colon cancer, or are symptomatic of a colon abnormality, undergo diagnostic testing rather than screening tests.
There are different types of screening tests for colorectal cancer: fecal (stool) occult blood testing, sigmoidoscopy, colonoscopy, digital colonoscopy, and DNA testing of the stool. The US Preventive Services Task Force (USPSTF) recommends strongly that screening begins at the age of 50 years for average-risk adults, but there is no specific recommendation for one screening test or strategy over another. The USPSTF advises that patients be offered a choice of screening options, using shared decision-making with the patient and physician to arrive at the best choice of screening programs for each individual.
Stool or fecal occult blood testing (FOBT)
Tumors of the colon and rectum tend to bleed slowly into the stool. The small amount of blood mixed into the stool usually is not visible to the naked eye. The commonly used stool occult blood tests rely on chemical color conversions to detect microscopic amounts of blood. These tests are both convenient and inexpensive. There are two kinds of fecal occult blood tests. The first is known as a guaiac FOBT. In this test, a small amount of stool is smeared on a special card for occult blood testing when a chemical is added to the card. Usually, three consecutive stool cards are collected. The other type of FOBT is an immunochemical test in which a special solution is added to the stool sample and analyzed in the laboratory using antibodies that can detect blood in a stool sample. The immunochemical test is a quantitative test that is more sensitive and specific for the diagnosis of polyps and cancer. It is preferred over the guaiac test.
A person who tests positive for stool occult blood has a 30%-45% chance of having a colon polyp and a 3%-5% chance of having colon cancer. Colon cancers found under these circumstances tend to be small and not to have spread and have a better long-term prognosis.
It is important to remember that having stool tested positive for occult blood does not necessarily mean a person has colon cancer. Many other conditions can cause occult blood in the stool. However, patients with a positive stool occult blood test should undergo further evaluations to exclude colon cancer and to explain the source of the bleeding. It is also important to realize that stool that has tested negative for occult blood does not mean that colorectal cancer or polyps do not exist. Even under ideal testing conditions, a significant percentage of colon cancers can be missed by stool occult blood screening. Many patients with colon polyps do not have positive stool occult blood. In patients suspected of having colorectal polyps and in those at higher risk for developing colorectal polyps and cancer, screening flexible sigmoidoscopies or colonoscopies are performed even if the FOBT is negative.
Flexible sigmoidoscopy and colonoscopy
Flexible sigmoidoscopy is an exam of the rectum and the lower colon (60 cm or about 2 feet in from the outside) using a viewing tube (a short version of colonoscopy). Research studies have shown that the use of screening flexible sigmoidoscopy can reduce mortality from colon cancer. This is a result of the detection of polyps or early cancers in people with no symptoms. If a polyp or cancer is found, a complete colonoscopy is recommended. The majority of colon polyps can be completely removed at the time of colonoscopy without surgery; however, polyps in the proximal colon that cannot be reached by the sigmoidoscope will be missed. Flexible sigmoidoscopy is often combined with fecal occult blood testing for colorectal cancer screening.
Colonoscopy uses a long (120 cm-150 cm) flexible tube, which can examine the entire length of the colon. Through this tube, the doctor (typically a gastroenterologist) can both view and take pictures of the entire colon and also can take biopsies of colon masses and remove polyps.
Patients with a high risk of developing colorectal cancer may undergo screening colonoscopies starting at earlier ages than 50. For example, patients with a family history of colon cancer are recommended to start screening colonoscopies at an age of 10 years before the earliest colon cancer is diagnosed in a first-degree relative or five years earlier than the earliest precancerous colon polyp discovered in a first-degree relative. Patients with hereditary colon cancer syndromes such as FAP, AFAP, HNPCC, and MYH are recommended to begin colonoscopies early. The recommendations differ depending on the genetic defect. For example, in people with FAP, colonoscopies may begin during their teenage years to look for the development of colon polyps. Patients with a prior history of polyps or colon cancer may also undergo colonoscopies to exclude recurrence. Patients with a long history (greater than 10 years) of chronic ulcerative colitis have an increased risk of colon cancer and should have regular colonoscopies to look for precancerous changes in the colon lining.
Virtual colonoscopy (computerized tomographic or CT colonography) has been utilized in the clinic as a screening technique for colorectal cancer. Virtual colonoscopy employs a CT scan using low doses of radiation with special software to visualize the inside of the colon and look for polyps or masses. The procedure typically involves a bowel preparation with laxatives and/or enemas (although not always) followed by a CT scan after air is introduced into the colon. Because no sedation is necessary, individuals can return to work or other activities upon completion of the test. Virtual colonoscopies appear to be equally able to detect larger polyps (over 1 centimeter in size) as regular colonoscopies. The virtual colonoscopy cannot be used to biopsy or remove tissue from the colon. A follow-up sigmoidoscopy or colonoscopy must be done to accomplish that.
Stool DNA testing
The Cologuard test is available in the U.S. for in-home sample collection for adults over 50 at average risk for colon cancer. The sample is sent to a laboratory for analysis of DNA changes in DNA from cells shed by the intestinal lining into the stool or hemoglobin in the sample. In a research study, the test was able to find 92% of colon cancers and 69% of precancers of the colon. False-negative and false-positive results are also possible.
American Cancer Society. "Colorectal Cancer." <https://www.cancer.org/cancer/colon-rectal-cancer.html>.
American College of Gastroenterology. "Colorectal Cancer." <https://gi.org/topics/colorectal-cancer/>.
Imperiale, T.F., D.F. Ransohoff, S.H. Itzkowitz, et al. "Multitarget stool DNA testing for colorectal-cancer screening." N Engl J Med 370.14 (2014): 1987-97.
United States. Centers for Disease Control and Prevention. "Colorectal cancer." Apr. 16, 2020. <https://www.cdc.gov/cancer/colorectal/>.
United States. National Cancer Institute. "Cancer Stat Facts: Colorectal Cancer." <https://seer.cancer.gov/statfacts/html/colorect.html>.
United States. National Cancer Institute. "Colorectal cancer." <https://www.cancer.gov/types/colorectal>.
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