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|Classification and external resources|
Diagram of the lower gastrointestinal tract
|ICD-O:||M8140/3 (95% of cases)|
|eMedicine||med/413 med/1994 ped/3037|
|Patient UK||Colorectal cancer|
|Classification and external resources|
Diagram of the lower gastrointestinal tract
|ICD-O:||M8140/3 (95% of cases)|
|eMedicine||med/413 med/1994 ped/3037|
|Patient UK||Colorectal cancer|
Colorectal cancer (also known as colon cancer, rectal cancer or bowel cancer) is when cancer develops in the colon or rectum (parts of the large intestine). It is due to the abnormal growth of cells that have the ability to invade or spread to other parts of the body. Signs and symptoms may include blood in the stool, a change in bowel movements, weight loss, and feeling tired all the time.
Most colorectal cancers are due to lifestyle factors and increasing age, with only a small number of cases due to underlying genetic disorders. Risk factors include diet, obesity, smoking, and not enough physical activity. Dietary factors that increase the risk include red and processed meat, as well as alcohol. Another risk factor is inflammatory bowel disease, which includes Crohn's disease and ulcerative colitis. Some of the inherited conditions that can cause colorectal cancer include: familial adenomatous polyposis and hereditary non-polyposis colon cancer; however, these represent less than 5% of cases. It typically starts as a benign tumor which over time becomes cancerous.
Bowel cancer may be diagnosed by obtaining a sample of the colon during a sigmoidoscopy or colonoscopy. This is then followed by medical imaging to determine if the disease has spread. Screening is effective at decreasing the chance of dying from colorectal cancer and is recommended starting at the age of 50 and continuing until the age of 75. Aspirin and other non-steroidal anti-inflammatory drugs decrease the risk. Their general use is not recommended for this purpose, however, due to side effects.
Treatments used for colorectal cancer may include some combination of surgery, radiation therapy, chemotherapy and targeted therapy. Cancers that are confined within the wall of the colon may be curable with surgery while cancer that has spread widely are usually not curable with management focusing on improving quality of life and symptoms. Five year survival rates in the United States are around 65%. This, however, depends on how advanced the cancer is, whether or not all the cancer can be removed with surgery, and the person's overall health. Globally, colorectal cancer is the third most common type of cancer making up about 10% of all cases. In 2012 there were 1.4 million new cases and 694,000 deaths from the disease. It is more common in developed countries, where more than 65% of cases are found. It is less common in women than men.
The symptoms and signs of colorectal cancer depend on the location of tumor in the bowel, and whether it has spread elsewhere in the body (metastasis). The classic warning signs include: worsening constipation, blood in the stool, decrease in stool caliber (thickness), loss of appetite, loss of weight, and nausea or vomiting in someone over 50 years old. While rectal bleeding or anemia are high-risk features in those over the age of 50, other commonly-described symptoms including weight loss and change in bowel habit are typically only concerning if associated with bleeding.
Greater than 75-95% of colon cancer occurs in people with little or no genetic risk. Other risk factors include older age, male gender, high intake of fat, alcohol or red meat, obesity, smoking, and a lack of physical exercise. Approximately 10% of cases are linked to insufficient activity. The risk for alcohol appears to increase at greater than one drink per day.
People with inflammatory bowel disease (ulcerative colitis and Crohn's disease) are at increased risk of colon cancer. The risk is greater the longer a person has had the disease, and the worse the severity of inflammation. In these high risk groups both prevention with aspirin and regular colonoscopies are recommended. People with inflammatory bowel disease account for less than 2% of colon cancer cases yearly. In those with Crohn's disease 2% get colorectal cancer after 10 years, 8% after 20 years, and 18% after 30 years. In those with ulcerative colitis approximately 16% develop either a cancer precursor or cancer of the colon over 30 years.
Those with a family history in two or more first-degree relatives (such as a parent or sibling) have a two to threefold greater risk of disease and this group accounts for about 20% of all cases. A number of genetic syndromes are also associated with higher rates of colorectal cancer. The most common of these is hereditary nonpolyposis colorectal cancer (HNPCC or Lynch syndrome) which is present in about 3% of people with colorectal cancer. Other syndromes that are strongly associated include: Gardner syndrome, and familial adenomatous polyposis (FAP) in which cancer nearly always occurs and is the cause of 1% of cases.
Most deaths due to colon cancer are associated with metastatic disease. A gene that appears to contribute to the potential for metastatic disease, metastasis associated in colon cancer 1 (MACC1), has been isolated. It is a transcriptional factor that influences the expression of hepatocyte growth factor. This gene is associated with the proliferation, invasion and scattering of colon cancer cells in cell culture and tumor growth and metastasis in mice. It has also been associated with the response to treatment.
Colorectal cancer is a disease originating from the epithelial cells lining the colon or rectum of the gastrointestinal tract, most frequently as a result of mutations in the Wnt signaling pathway that artificially increase signaling activity. The mutations can be inherited or acquired, and most probably occur in the intestinal crypt stem cell.[not in citation given] The most commonly mutated gene in all colorectal cancer is the APC gene, which produces the APC protein. The APC protein is a "brake" on the accumulation of β-catenin protein; without APC, β-catenin accumulates to high levels and translocates (moves) into the nucleus, binds to DNA, and activates the transcription of genes that are normally important for stem cell renewal and differentiation but when inappropriately expressed at high levels can cause cancer. While APC is mutated in most colon cancers, some cancers have increased β-catenin because of mutations in β-catenin (CTNNB1) that block its breakdown, or they have mutation(s) in other genes with function similar to APC such as AXIN1, AXIN2, TCF7L2, or NKD1.
Beyond the defects in the Wnt-APC-beta-catenin signaling pathway, other mutations must occur for the cell to become cancerous. The p53 protein, produced by the TP53 gene, normally monitors cell division and kills cells if they have Wnt pathway defects. Eventually, a cell line acquires a mutation in the TP53 gene and transforms the tissue from an benign epithelial tumor into an invasive epithelial cell cancer. (Sometimes the gene encoding p53 is not mutated, but another protective protein named BAX is.)
Other proteins responsible for cell suicide that are commonly deactivated in colorectal cancers are TGF-β and DCC (Deleted in Colorectal Cancer). TGF-β has a deactivating mutation in at least half of colorectal cancers. Sometimes TGF-β is not deactivated, but a downstream protein named SMAD is. DCC commonly has deletion of its chromosome segment in colorectal cancer.
Some genes are oncogenes - they are overexpressed in colorectal cancer. For example, genes encoding the proteins KRAS, RAF, and PI3K, which normally stimulate the cell to divide in response to growth factors, can acquire mutations that result in over-activation of cell proliferation. The chronological order of mutations is sometimes important, with a primary KRAS mutation generally leading to a self-limiting hyperplastic or borderline lesion, but if occurring after a previous APC mutation it often progresses to cancer. PTEN, a tumor suppressor, normally inhibits PI3K, but can sometimes become mutated and deactivated.
Comprehensive, genome-scale analysis has revealed that colorectal carcinomas are clearly separable into hypermutated and non-hypermutated tumor types. In addition to the oncogenic and inactivating mutations described for the genes above, non-hypermutated samples also contain mutated CTNNB1, FAM123B, SOX9, ATM, and ARID1A. Progressing through a distinct set of genetic events, hypermutated tumors display mutated forms of ACVR2A, TGFBR2, MSH3, MSH6, SLC9A9, TCF7L2, and BRAF. The common theme among these genes, across both tumor types, is their involvement in WNT and TGF-β signaling pathways, which in turn results in increased activity of MYC, a central player in colorectal cancer.
The term "field cancerization" was first used in 1953 to describe an area or "field" of epithelium that has been preconditioned by (at that time) largely unknown processes so as to predispose it towards development of cancer. Since then, the terms "field cancerization", "field carcinogenesis", "field defect", and "field effect" have been used to describe pre-malignant or pre-neoplastic tissue in which new cancers are likely to arise.
However, in most cancer research, as pointed out by Rubin "The vast majority of studies in cancer research has been done on well-defined tumors in vivo, or on discrete neoplastic foci in vitro. Yet there is evidence that more than 80% of the somatic mutations found in mutator phenotype human colorectal tumors occur before the onset of terminal clonal expansion." Similarly, Vogelstein et al. point out that more than half of somatic mutations identified in tumors occurred in a pre-neoplastic phase (in a field defect), during growth of apparently normal cells. Likewise, epigenetic alterations present in tumors may have occurred in pre-neoplastic field defects.
An expanded view of field effect has been termed "etiologic field effect", which encompasses not only molecular and pathologic changes in pre-neoplastic cells but also influences of exogenous environmental factors and molecular changes in the local microenvironment on neoplastic evolution from tumor initiation to death.
Epigenetic alterations are much more frequent in colon cancer than genetic (mutational) alterations. As described by Vogelstein et al., an average cancer of the colon has only 1 or 2 oncogene mutations and 1 to 5 tumor suppressor mutations (together designated “driver mutations”), with about 60 further “passenger” mutations. The oncogenes and tumor suppressor genes are well studied and are described below under Pathogenesis.
However, by comparison, epigenetic alterations in colon cancers are frequent and affect hundreds of genes. For instance, there are types of small RNAs called microRNAs that are about 22 nucleotides long. These microRNAs (or miRNAs) do not code for proteins, but they can “target” protein coding genes and reduce their expression. Expression of these miRNAs can be epigenetically altered. As one example, the epigenetic alteration consisting of CpG island methylation of the DNA sequence encoding miR-137 reduces its expression, and this is a frequent early epigenetic event in colorectal carcinogenesis, occurring in 81% of colon cancers and in 14% of the normal appearing colonic mucosa adjacent to the cancers. The altered adjacent tissues associated with these cancers are called field defects. Silencing of miR-137 can affect expression of about 500 genes, the targets of this miRNA.
Changes in the level of miR-137 expression result in changed mRNA expression of the target genes by 2 to 20-fold and corresponding, though often smaller, changes in expression of the protein products of the genes. Other microRNAs, with likely comparable numbers of target genes, are even more frequently epigenetically altered in colonic field defects and in the colon cancers that arise from them. These include miR-124a, miR-34b/c and miR-342 which are silenced by CpG island methylation of their encoding DNA sequences in primary tumors at rates of 99%, 93% and 86%, respectively, and in the adjacent normal appearing mucosa at rates of 59%, 26% and 56%, respectively.
In addition to epigenetic alteration of expression of miRNAs, other common types of epigenetic alterations in cancers that change gene expression levels include direct hypermethylation or hypomethylation of CpG islands of protein-encoding genes and alterations in histones and chromosomal architecture that influence gene expression. As an example, 147 hypermethylations and 27 hypomethylations of protein coding genes were frequently associated with colorectal cancers. Of the hypermethylated genes, 10 were hypermethylated in 100% of colon cancers, and many others were hypermethylated in more than 50% of colon cancers. In addition, 11 hypermethylations and 96 hypomethylations of miRNAs were also associated with colorectal cancers.
As summarized in the articles Carcinogenesis and Neoplasm, for sporadic cancers in general, a deficiency in DNA repair is occasionally due to a mutation in a DNA repair gene, but is much more frequently due to epigenetic alterations that reduce or silence expression of DNA repair genes.
Diagnosis of colorectal cancer is via sampling of areas of the colon suspicious for possible tumor development typically done during colonoscopy or sigmoidoscopy, depending on the location of the lesion. The extent of the disease is then usually determined by a CT scan of the chest, abdomen and pelvis. There are other potential imaging test such as PET and MRI which may be used in certain cases. Colon cancer staging is done next and based on the TNM system which is determined by how much the initial tumor has spread, if and where lymph nodes are involved, and the extent of metastatic disease.
The microscopic cellular characteristics of the tumor are usually reported from the analysis of tissue taken from a biopsy or surgery. A pathology report will usually contain a description of cell type and grade. The most common colon cancer cell type is adenocarcinoma which accounts for 98% of cases. Other, rarer types include lymphoma and squamous cell carcinoma.
Cancers on the right side of the large intestine (ascending colon and cecum) tend to be exophytic, that is, the tumor grows outwards from one location in the bowel wall. This very rarely causes obstruction of feces, and presents with symptoms such as anemia. Left-sided tumors tend to be circumferential, and can obstruct the bowel lumen much like a napkin ring which can present with thinner caliber stools.
Adenocarcinoma is a malignant epithelial tumor, originating from superficial glandular epithelial cells lining the colon and rectum. It invades the wall, infiltrating the muscularis mucosae layer, the submucosa, and then the muscularis propria. Tumor cells describe irregular tubular structures, harboring pluristratification, multiple lumens, reduced stroma ("back to back" aspect). Sometimes, tumor cells are discohesive and secrete mucus, which invades the interstitium producing large pools of mucus/colloid (optically "empty" spaces) - mucinous (colloid) adenocarcinoma, poorly differentiated. If the mucus remains inside the tumor cell, it pushes the nucleus at the periphery - "signet-ring cell." Depending on glandular architecture, cellular pleomorphism, and mucosecretion of the predominant pattern, adenocarcinoma may present three degrees of differentiation: well, moderately, and poorly differentiated.
Most (50%) colorectal adenomas and (80-90%) colorectal cancer tumors are thought over express the cyclooxygenase-2 (COX-2) enzyme. This enzyme is generally not found in healthy colon tissue, but is thought to fuel abnormal cell growth.
PET/CT of a staging exam of colon carcinoma. Besides the primary tumor a lot of lesions can be seen. On cursor position: lung nodule.
Precancer — Tubular adenoma (left of image), a type of colonic polyp and a precursor of colorectal cancer. Normal colorectal mucosa is seen on the right.
Precancer — Colorectal villous adenoma.
The colon cancer staging can be made according to the TNM staging system from the WHO organization, the UICC and the AJCC. The Astler-Coller classification (1954) or the Dukes classification (1932) are now less used.
Tumor budding in colorectal cancer is loosely defined by the presence of individual cells and small clusters of tumor cells at the invasive front of carcinomas. It has been postulated to represent an epithelial–mesenchymal transition (EMT). Tumor budding is a well-established independent marker of a potentially poor outcome in colorectal carcinoma that may allow for dividing people into risk categories more meaningful than those defined by TNM staging, and also potentially guide treatment decisions, especially in T1 and T3 N0 (Stage II, Dukes’ B) colorectal carcinoma. Unfortunately, its universal acceptance as a reportable factor has been held back by a lack of definitional uniformity with respect to both qualitative and quantitative aspects of tumor budding.
Current dietary recommendations to prevent colorectal cancer include increasing the consumption of whole grains, fruits and vegetables, and reducing the intake of red meat. The evidence for fiber and fruits and vegetables however is poor. Physical activity can moderately reduce the risk of colorectal cancer.
Aspirin and celecoxib appear to decrease the risk of colorectal cancer in those at high risk. However, it is not recommended in those at average risk. There is tentative evidence for calcium supplementation but it is not sufficient to make a recommendation. Vitamin D intake and blood levels are associated with a lower risk of colon cancer.
More than 80% of colorectal cancers arise from adenomatous polyps making this cancer suitable for screening. Diagnosis of cases of colorectal cancer through screening tends to occur 2–3 years before diagnosis of cases with symptoms. Screening has the potential to reduce colorectal cancer deaths by 60%.
Medical societies recommend screening between the age of 50 and 75 years with sigmoidoscopy every 5 years and colonoscopy every 10 years. For those at high risk, screenings usually begin at around 40. It is unclear which of these two methods is better. Colonoscopy may find more cancers in the first part of the colon but is associated with greater cost and more complications. For people with average risk who have had a high-quality colonoscopy with normal results, the American Gastroenterological Association does not recommend any type of screening in the 10 years following the colonoscopy. For people over 75 or those with a life expectancy of less than 10 years, screening is not recommended.
The three main screening tests are fecal occult blood testing, flexible sigmoidoscopy, and colonoscopy. Of the three, only sigmoidoscopy cannot screen the right side of the colon where 42% of malignancies are found. Virtual colonoscopy via a CT scan appears as good as standard colonoscopy for detecting cancers and large adenomas but is expensive, associated with radiation exposure, and cannot remove any detected abnormal growths like standard colonoscopy can.
Fecal occult blood testing (FOBT) of the stool is typically recommended every two years and can be either guaiac based or immunochemical. Annual FOBT screening results in a 16% relative reduction in colorectal cancer mortality, but no difference in all-cause mortality. Immunochemical tests are highly accurate and do not require dietary or medication changes before testing.
The M2-PK Test identifies an enzyme in colorectal cancers and polyps rather than blood in the stool. It does not require any special preparation prior to testing. M2-PK is sensitive for colorectal cancer and polyps and is able to detect bleeding and non-bleeding colorectal cancer and polyps. In the event of a positive result people would be asked to undergo further examination e.g. colonoscopy.
The treatment of colorectal cancer can be aimed at curation or palliation. The decision on which aim to adopt depends on various factors, including the person's health and preferences, as well as the stage of the tumor. When colorectal cancer is caught early, surgery can be curative. However, when it is detected at later stages (for which metastases are present), this is less likely and treatment is often directed at palliation, to relieve symptoms caused by the tumour and keep the person as comfortable as possible.
For people with localized cancer, the preferred treatment is complete surgical removal with adequate margins, with the attempt of achieving a cure. This can either be done by an open laparotomy or sometimes laparoscopically. If there are only a few metastases in the liver or lungs they may also be removed. Sometimes chemotherapy is used before surgery to shrink the cancer before attempting to remove it. The two most common sites of recurrence of colorectal cancer is in the liver and lungs.
If cancer has entered the lymph nodes, adding the chemotherapy agents fluorouracil or capecitabine increases life expectancy. If the lymph nodes do not contain cancer, the benefits of chemotherapy are controversial. If the cancer is widely metastatic or unresectable, treatment is then palliative. Typically in this setting, a number of different chemotherapy medications may be used. Chemotherapy drugs for this condition may include capecitabine, fluorouracil, irinotecan, leucovorin, oxaliplatin and UFT. Another type of agent that is sometimes used are the epidermal growth factor receptor inhibitors.
While a combination of radiation and chemotherapy may be useful for rectal cancer, its use in colon cancer is not routine due to the sensitivity of the bowels to radiation. Just as for chemotherapy, radiotherapy can be used in the neoadjuvant and adjuvant setting for some stages of rectal cancer.
Palliative care is medical care which focuses on treatment of symptoms from serious illness, like cancer, and improving quality of life. Palliative care is recommended for any person who has advanced colon cancer or has significant symptoms.
Involvement of palliative care may be beneficial to improve the quality of life for both the person and his or her family, by improving symptoms, anxiety and preventing admissions to the hospital.
In people with incurable colorectal cancer, palliative care can consist of procedures that relieve symptoms or complications from the cancer but do not attempt to cure the underlying cancer, thereby improving quality of life. Surgical options may include non-curative surgical removal of some of the cancer tissue, bypassing part of the intestines, or stent placement. These procedures can be considered to improve symptoms and reduce complications such as bleeding from the tumor, abdominal pain and intestinal obstruction. Non-operative methods of symptomatic treatment include radiation therapy to decrease tumor size as well as pain medications.
Survival is directly related to detection and the type of cancer involved, but overall is poor for symptomatic cancers, as they are typically quite advanced. Survival rates for early stage detection is about 5 times that of late stage cancers. People with a tumor that has not breached the muscularis mucosa (TNM stage Tis, N0, M0) have a 5-year survival of 100%, while those with invasive cancer of T1 (within the submucosal layer) or T2 (within the muscular layer) have an average 5-year survival of approximately 90%. Those with a more invasive tumor yet without node involvement (T3-4, N0, M0) have an average 5-year survival of approximately 70%. Patients with positive regional lymph nodes (any T, N1-3, M0) have an average 5-year survival of approximately 40%, while those with distant metastases (any T, any N, M1) have an average 5-year survival of approximately 5%.
According to American Cancer Society statistics in 2006, over 20% of people with colorectaol cancer come to medical attention when the disease is already advanced (stage IV), and up to 25% of this group will have isolated liver metastasis that is potentially resectable. In this selective group, those who undergo curative resection experience a 5-year survival outcome in a third of the cases.
The aims of follow-up are to diagnose, in the earliest possible stage, any metastasis or tumors that develop later, but did not originate from the original cancer (metachronous lesions).
The U.S. National Comprehensive Cancer Network and American Society of Clinical Oncology provide guidelines for the follow-up of colon cancer. A medical history and physical examination are recommended every 3 to 6 months for 2 years, then every 6 months for 5 years. Carcinoembryonic antigen blood level measurements follow the same timing, but are only advised for people with T2 or greater lesions who are candidates for intervention. A CT-scan of the chest, abdomen and pelvis can be considered annually for the first 3 years for patients who are at high risk of recurrence (for example, those who had poorly differentiated tumors or venous or lymphatic invasion) and are candidates for curative surgery (with the aim to cure). A colonoscopy can be done after 1 year, except if it could not be done during the initial staging because of an obstructing mass, in which case it should be performed after 3 to 6 months. If a villous polyp, a polyp >1 centimeter or high grade dysplasia is found, it can be repeated after 3 years, then every 5 years. For other abnormalities, the colonoscopy can be repeated after 1 year.
Routine PET or ultrasound scanning, chest X-rays, complete blood count or liver function tests are not recommended. These guidelines are based on recent meta-analyses showing intensive surveillance and close follow-up can reduce the 5-year mortality rate from 37% to 30%.
Globally more than 1 million people get colorectal cancer every year resulting in about 715,000 deaths as of 2010 up from 490,000 in 1990. As of 2012 it is the second most common cause of cancer in women (9.2% of diagnoses) and the third most common in men (10.0%) with it being the fourth most common cause of cancer death after lung, stomach, and liver cancer. It is more common in developed than developing countries. Globally incidences vary 10-fold with highest rates in the Australia, New Zealand, Europe and the US and lowest rates in Africa and South-Central Asia.
Based on rates from 2007-2009, 4.96% of US men and women born today will be diagnosed with colorectal cancer during their lifetime. From 2005-2009, the median age at diagnosis for cancer of the colon and rectum in the US was 69 years of age. Approximately 0.1% were diagnosed under age 20; 1.1% between 20 and 34; 4.0% between 35 and 44; 13.4% between 45 and 54; 20.4% between 55 and 64; 24.0% between 65 and 74; 25.0% between 75 and 84; and 12.0% 85+ years of age. Rates are higher among males (54 per 100,000 c.f. 40 per 100,000 for females).
In the United States, March is colorectal cancer awareness month.
Preliminary in-vitro evidence suggests lactic acid bacteria (e.g., lactobacilli, streptococci or lactococci) may be protective against the development and progression of colorectal cancer through several mechanisms such as antioxidant activity, immunomodulation, promoting programmed cell death, antiproliferative effects, and epigenetic modification of cancer cells.
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