The Beginning of New Normal
Born in Washington State in 1929, Jackie Sutton was a normal and happy little girl who loved playing outdoors and with her sisters, Donna and Helen, and younger brother Rupert. She was relatively healthy growing up and besides the early death of her sister, Donna, of a lung infection there were no histories of any health risks, hereditary diseases, or familial cancers. In 1941 her family moved to Missouri and in 1950 she married her high school sweetheart, Richard. After the birth of her third child in 1967, Jackie was diagnosed with ulcerative colitis—an irritable bowel disease (IBD). Ulcerative colitis is a failing of the immune system that is often exacerbated by poor diet and stress. It is characterized by bloody stools, fatigue, and abdominal pain and cramping. In 2000, Jackie had been married for 50 years and was the mother of three and grandmother of two children. She and her husband, Richard, had recently retired from The Boeing Company, where Jackie had worked as a secretary for many years. She enjoyed traveling and visiting her children and grandchildren.

At 70 years old, Jackie frequently has her colon screened for abnormalities or polyps due to her long history of IBD. On June 6, 2000, her routine colonoscopy reveals an ulcerating sore about 10-12 mm in diameter in her cecum as well as polyps in her transverse colon. The cecum is the pouch-like structure where undigested food is collected at the beginning of the colon (see Figure 1). The cecal tumor is biopsied and her attending physician, Dr. James Wagner, writes, “I’m sure it is adenocarcinoma.”

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Figure 1: Diagram of Colon

Ninety-five percent of all colorectal cancers are adenocarcinomas of the colon, making this the most common form of colorectal cancer in adults; there are 140,000 new cases each year. [1] [2] The cancer originates in the glandular cells of the colon, spreading first to the colon wall and eventually metastasizing to other organs via the lymphatic system. These glandular cells produce mucus and are found throughout the body, including the lung, prostate, pancreas, esophagus, and colon/rectum. In colon cancer, the malfunction of the glandular cells often results in an excess of mucin excretion—a protein that helps to lubricate the interior of the colon and digestive tract. Colon cancer with this phenotype is referred to as mucinous or colloid adenocarcinoma. [3] The cancer is most often seen in adults with a family history of adenomatous polyposis or Gardner’s syndrome—both of which cause excess growth of colon and rectal polyps. A polyp is excess growth into the empty space of the colon (lumen), although not cancerous, polyps can eventually lead to tumors and cancerous masses. Diet also can have a strong effect on the likelihood of developing adenocarcinoma—diets high in fat and beef content and low in fiber have been linked to increased risk of developing the cancer.[4] Older adults, past the age of 50, are also at risk as 30% of people over 50 harbor colon or rectal polyps.[5] Other risk factors include previous cancer and irritable bowel syndrome. [6]

Fortunately, the adenocarcinoma of the colon is rarely fast growing and many people do not even realize that they have the disease until they undergo a routine colonoscopy. Symptoms can take years to appear and include rectal bleeding, bowel obstruction, angina, fatigue, shortness of breath, changes in bowel habits, abdominal discomfort, and anemia.[7] Prognosis is generally good if the cancer is caught in the early stages, with a survival rate of 70-80% for the first five years. [8] Total patient survival rate past five years is estimated at 50%.[9]

In Jackie’s case, the cancer most likely developed as a result of her 33-year history of colitis. Ulcerative colitis is a debilitating disease that develops overtime usually in adults. It is characterized by the chronic inflammation and formation of sores in the innermost lining of the large intestine or colon. There is no known cure for ulcerative colitis, but it is treatable and has the possibility of long-term remission periods. There are two factors linked to increased cancer risk: disease duration and extent of colon inflammation. The risk for developing a colorectal cancer doesn’t vary from the general population until 8-10 years have passed from the first diagnosis of IBD[10] . If the inflammation is found in the colon, and is not limited to the bottom of the rectum, there is a higher risk for developing some form of colorectal cancer. Even those who enter remission retain the risk for developing a cancer related to their IBD.

Cancer is one of the most ancient and feared human diseases; and there are few words more dreaded than a physician’s diagnosis of cancer. In those few seconds, a line is drawn between the patient’s life before cancer and the war they now find themselves in; it is the boundary between the old and the new normal. At the age of 70, Jackie has developed invasive adenocarcinoma with a malignant mass located in the cecum of her colon. Within a week, her life and the lives of her husband and children are turned upside down. Family vacations are canceled, and her oldest son quits his high-powered job in Singapore and moves his family back to the United States to be close to his mother as she struggles through her cancer treatments. Since her cancer has not metastasized to other areas of her body and is localized solely to the colon, she is still in the first stage of adenocarcinoma. Because her doctors have diagnosed her cancer early, Jackie’s prognosis is good—but it will take many months of aggressive treatment before she is deemed cancer free and enters remission.

Screening
Being diagnosed with cancer is a frightening experience and affects not only the patient but also her surrounding family and friends. In Jackie’s case, her life and the lives of her husband and children were uprooted as she was diagnosed and began the arduous process of being treated for adenocarcinoma of the colon. For most colon cancer patients the treatment is very standardized and is based on the stage the cancer is in when it is discovered. If discovered early enough the prognosis is good with a survival rate past five years of 70-80%.[11] The key is to catch the cancer with frequent screening techniques before it spreads and metastasizes to other organs.

Unlike some cancers, adenocarcinoma of the colon is easily detected using a variety of screening techniques. Patients with a family history of the disease, irritable bowel disease, or who are over the age of 50 should be screened regularly. There are three methods of screening for colon cancer that are endorsed by the US Preventative Services Task Force and other medical associations; these include fecal occult blood tests (FOBT), sigmoidoscopy, or colonoscopy.

Fecal occult blood tests detect trace amounts of human blood in the feces of a patient. Since tumors and cancerous polyps often bleed, detecting blood in the feces at concentration greater than 2-3mg/gram of stool increases the possibility of cancer.[12] The Food and Drug Administration (FDA) has approved two versions of the test: the guaiac FOBT and the fecal immunochemical test (FIT). The guaiac FOBT uses a chemical reaction to detect trace amounts of heme, a component of the oxygen-carrying protein in red blood cells—hemoglobin. The FIT version of FOBT also detects the presence of blood by screening for hemoglobin, in this instance however, antibodies are used.

Sigmoidoscopy and colonoscopy are both invasive procedures that involve the insertion of a camera into the rectum of an anesthetized patient in order to assess the health of the epithelial lining of the colon. A colonoscopy involves the entirety of the colon and rectum, while a sigmoidoscopy assesses only the lower part of the colon. During both tests, gastroenterologists look for polyps, tears, unusual masses, and inflammation as indicators of cancer. If a doctor does find a polyp they will often remove it during the procedure, if a larger mass is found, the doctor may take a biopsy for further analysis. If a person is at average risk for developing colorectal cancer then most doctors will suggest screening their patients every ten years.[13]

In all health decisions, and particularly in the case of cancer, a patient should always work in partnership with her physician—educating herself about her illnesses and risk factors for disease. It was exactly this type of cooperative teamwork that was responsible for Jackie’s early adenocarcinoma diagnosis in 2000. Since Jackie knew that her IBD put her at risk for colorectal cancer, she visited her doctor frequently for screening. In early June of 2000, Jackie insisted that her doctor perform a full colonoscopy instead of a sigmoidoscopy. Luckily, he agreed with his patient and performed the procedure that found the malignant tumor hiding in her cecum at the end of her colon. If Jackie had not taken the time to research her health risks and medical procedures she would never have insisted on a full colon screening and would probably not be alive today. Since the symptoms of colorectal cancer are subtle and usually do not appear until later stages of the disease, screening and patient education are two of the most important preventative measures that can be taken when diagnosing and treating adenocarcinoma of the colon.

Treatment
Once a colorectal cancer has been detected using one of the three standard procedures discussed previously, the treatment plan varies based on the stage of the cancer at the time of diagnosis. A stage 0 adenocarcinoma of the colon is defined as a cancer that has not expanded beyond the lining of the colon and most physicians will simply remove the malignant polyp (polypectomy) or mass during the colonoscopy/sigmoidoscopy procedure.[14] Stage I adenocarcinoma is stilled localized to the colon but has now spread through many layers of the colon wall. If the cancer originated from a polyp most physicians will still attempt to remove it during routine screening, if there are cancerous cells left behind or if the cancer did not originate from a polyp, a partial colectomy might be performed.[15] A partial colectomy is a surgery that removes the section of the colon that has become cancerous; occasionally the surrounding lymph nodes are also removed.

Treatment options for adenocarcinoma in the second stage become much more aggressive and tend to use combinations of surgical and chemotherapeutic techniques. When the cancer has spread to other tissues beyond the colon but has not yet reached the lymph nodes it is diagnosed as stage II cancer. In this case surgery is still the primary treatment, but it is usually followed by chemotherapy (adjuvant chemotherapy) if the cancerous mass looked particularly abnormal during biopsy, had spread to other organs, the cancer had obstructed the gastrointestinal tract, or had caused a hole in the wall of the colon.[16] There are a few options for chemotherapy at this point in treatment, one of the more common drugs given is 5-Fluorouracil (5-FU)—an antimetabolite that when integrated into the cell’s structure prevents cell division.[17] It acts as a uracil analog that when incorporated into RNA inhibits the translation of proteins.[18] 5-FU also acts as an inhibitor of the protein thymidylate synthase (TS), which is the key enzyme in the de novo synthesis of pyrimidines. If TS is inhibited then the cell cannot make certain nucleic acids (thymine, cytosine, and uracil) and the replication of DNA and DNA repair mechanisms are decreased. 5-FU is often taken with leucovorin, an analog of folic acid, which seems to enhance the anti-cancer properties of 5-FU.[19] Leucovorin assists in the inhibition of TS by increasing the affinity of 5-FU for the active site of TS, this increases the half-life of the 5-FU, allowing it to stay in the body longer. The importance of using chemotherapy once the cancer has begun to spread is best explained by viewing the tumor as a collection of cells in a competitive environment. When a large portion of this population is removed via surgery many of the resources that were once scarce due to high population of cancer cells become available to the few cancerous cells that might be left behind. This can result in a second tumor. The chemotherapy is prescribed in the hope that any cancer cells not removed in surgery will be killed chemically and preventing them from moving into the newly available niche.

Stage III adenocarcinoma of the colon is characterized by the spread to the lymphatic system. Most oncologists will try to surgically remove the cancerous tissue as well as the affected lymph nodes. Adjuvant chemotherapy is almost always used and includes combinations of 5-FU with leucovorin and oxaliplatin. Oxaliplatin binds to the guanine and cytosine moieties of DNA; this causes cross-linking of the double helix and prevents transcriptive and replicative mechanisms.[20] The combination of these three drugs is called FOLFOX.[21] The other chemotherapeutic option is a cocktail called CapeOx.[22] CapeOx is the administration of both oxaliplatin and capecitabine. Capecitabine is another anti-metabolite that is a prodrug form of 5-FU.[23] A prodrug is a molecule that is metabolized by the body to become an active compound; in this case capecitabine becomes 5-FU.

Stage IV adenocarcinoma means that the cancer has metastasized to distal organs and tissues, usually the lymphatic system, the liver, the lungs, and/or the lining of the abdominal cavity. At this stage, surgery is considered futile and the main treatment is chemotherapy. Surgery is used however, if the cancer has completely obstructed the GI tract to relieve symptoms of the patient. A colostomy can be performed where the colon is removed and waste products are diverted out through the abdomen and into a colostomy bag. Chemotherapeutic treatments are used before and after symptom-relieving surgery. Most treatments involve some combination of the drugs used in FOLFOX or CapeOx. For pain relief, radiation therapy is occasionally used to shrink the tumors temporarily. The goal of most treatments during stage IV adenocarcinoma is to relieve symptoms and prolong the quality of life—not to cure the patient.

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Figure 2: Metabolic conversion of Capecitabine to 5-Fluorouracil
On first inspection, Jackie’s cancer appeared to be localized to the interior of her colon. As soon as her gastroenterologist realized that the abnormal mass in her colon was indeed an adenocarcinoma, he had her scheduled for surgery. A month after her diagnosis, Jackie had 8 inches of her colon removed as well as 21 lymph nodes. During the routine biopsy of the surgically removed tissue, one cancer cell was found in a lymph node. This made the cancer diagnosis more severe as the disease had entered Jackie’s lymphatic system and her doctor suggested that she begin a chemotherapy regime to ensure that the cancer was completely gone. Jackie immediately started with intensive chemotherapy treatment with CapeOx. CapeOx was chosen over FOLFOX because of capecitabine’s prodrug qualities. As mentioned before, capecitabine is converted to the cytotoxic molecule 5-Fluoruracil once it has entered the patient’s body. The final two enzymes that complete this metabolic transition, cytidine deaminase and thymidine phosphorylase (see figure 2), are up regulated in tumor tissue.[24] This allows the drug to only become its active (and toxic) form when it has entered the site of cancer. This localization of chemotherapy decreases the side effects and the death of healthy cells, meaning that the majority of the drug is used against the tumor and not the patient’s healthy tissues and organs. For a patient of Jackie’s age and delicate health, localizing the chemotherapy to the tumor to reduce side effects is a priority.

Despite the use of the prodrug, Jackie’s body reacted very poorly to the chemo and there were times where her doctors were unable to administer the next medications because she was too ill from the previous dose. This was a very difficult time for Jackie and her family and her doctors were not sure she would be able to complete the entire chemotherapy program. After nine months however, her chemotherapy ended and she was declared to be in remission. Even though Jackie has been “cured” of her cancer, she still receives yearly colonoscopies—always aware that the cancer might still reappear.

Utilizing the Molecular Biology of a Cancer
When diagnosed with cancer, one of the first questions patients ask their doctor is, “Why did this happen to me?” The answer to this question is one that scientists, physicians, and the entire cancer pharmaceutical industry is still attempting to explain. In many cases, we cannot say what specifically caused one person to get cancer as opposed to another, but science is getting closer to identifying the risk factors and molecular mechanisms of various cancer types.

In the case of our patient, Jackie, the cancer was most likely a result of her thirty-year history with ulcerative colitis, a disease that causes chronic bowel inflammation. Scientists have been correlating inflammation with increased risk of cancer for the last decade.[25] Our inflammatory reaction is often one of the first responders in our body’s immune system when we are threatened by microbial invasion or require tissue repair and regeneration.[26] In a healthy system, the inflammatory response is only activated for a short period of time; longitudinal studies have correlated extended inflammatory period with the development of cancerous masses.[27]

This was an unexpected finding; in most cases our immune systems are our defenses against external invaders as well as internal malfunctions. The paradox of an immune system that was actively promoting the genesis and proliferation of cancers first began to appear in the early 2000s. In the past decade the research in this new field, tumor-promoting immune systems, has expanded and it is now widely believed that the different branches of the immune system are integral players in tumorigenesis and progression.

Although the mechanisms by which inflammation causes cancer is not always clear, one possibility is the release of genomic damaging materials. These materials, called free radicals, are responsible for the damage of DNA, which can increase the risk of mutation. Free radicals, or more specifically, hydroxyl radical, superoxide, nitric oxide, and peroxynitrite, are made by enzymes such as myeloperoxidase and NADPH oxidase, which are up-regulated by inflammatory signaling pathways. These DNA damaging free radicals are usually used to fight off microbial invasion but could potentially be present in other cases of inflammation.[28]

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Figure 3: Methylation can silence a gene.
In many non-hereditary colorectal cancers, a gene called MLH1 is often epigenetically silenced. Epigenetics is the “heritable changes in gene expression (active versus inactive genes) that does not involve changes to the underlying DNA sequence.”[29] In the case of MLH1, the promoter region is methylated so that transcription does not occur and the gene’s products cannot be expressed. MLH1 is a tumor suppressor gene that is responsible for DNA mismatch repair processes. Since MLH1 is involved in DNA repair, its loss in the precancerous cell can result in increased mutation rates, this is commonly referred to as microsatellite instability (MSI). While loss of mismatch repair genes is often found in hereditary cancers such as Lynch Syndrome, the methylation of MLH1 promoter is found in nonhereditary or sporadic adenocarcinomas and accounts for 20% of all colorectal cancers.[30] Once the DNA is made vulnerable by the loss of its repair functions, environmental factors such as poor diet or chronic inflammation can lead to irreparable damage.

In 70% of the sporadic colon cancers with methylated MLH1 promoters, there were found to be mutations in the BRAF gene.[31] B-Raf, the product of the BRAF gene, is involved in cell signaling and when mutated can result in over activity of the signaling cascade and thus cancer. Since this mutation seems to be unique to non-hereditary colorectal cancer, both BRAF and MLH1 are commonly screened to rule out a genetic predisposition to colon cancer. The role that BRAF plays in the formation of adenocarcinoma in cells with damaged mismatch repair genes is still unknown. In a recent study, patients found with both hypermethylation of MLH1 promoter and BRAF mutations the prognosis was significantly worse than those with wildtype BRAF genes.[32]

The increased mutability of Jackie’s colon cells is part of the reason her doctors chose to put her on CapeOx. As stated before, CapeOx is a chemotherapeutic cocktail that contains the drug capecitabine. Capecitabine is the prodrug version of 5-fluorouracil, an antimetabolite that damages the cell when incorporated into the DNA and RNA structures. Every time 5-fluoruracil damages the cell’s DNA there is an opportunity for a mutation to occur. Once enough mutations have accumulated the cell will trigger apoptosis and die. Because capecitabine is not active until after it has been metabolized, it produces less side effects than 5-fluoruracil. The enzymes that cause this conversion are upregulated in cancer cells, meaning that only the cancerous cells will receive the full dose of treatment. This means that fewer healthy cells are targeted for destruction. This reduces the risk of a secondary cancer forming due to the chemotherapy. Since Jackie’s genes are already vulnerable due to the hypermethylation of her mismatch repair promoter, she cannot risk cells being damaged by the chemotherapy and producing a second cancer.

Proactive (not Powerless!) PatientsAdenocarcinoma of the colon affects 140,000 people a year.[33] But there is good news; if caught early, survival rates are high and 70-80% of individuals will make it past the first five years.[34] The key to preventing and surviving adenocarcinoma of the colon is early detection and there are currently four approved methods with the most accurate being the full colonoscopy. People who are at a higher risk for colon cancer should speak with their doctors about frequent screening, and those without high risk factors should be screened every ten years after the age of 50. Unlike many other cancers, the patient has a lot of control in the prevention and treatment of colorectal cancer. Because the colon is part of the digestive tract, preventing colon cancer involves good dietary and exercise habits. Diets high in red meat and fat have been linked to increased incidence of colorectal cancers, while diets with plenty of vegetables, fruits, and fiber are linked to decreased incidence. Although being diagnosed with cancer can make a patient feel powerless, it is important to remember that there are proactive steps you can take during and after treatment that can greatly reduce your risk of cancer recurrence. These include frequent screenings, fibrous and vegetable rich diets as well as decreased meat and alcohol consumption. Be proactive! As we saw in Jackie’s case, the patient has a lot of control in protecting herself from colorectal lesions—if you or someone you know is at risk for colon cancer because of familial history, IBD, or poor diet, talk to your doctor about a routine colonoscopy. Healthy diets and frequent screening can save lives.
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Figure 4: Fifteen-Year Survivor, Jackie, with her daughter and granddaughter in February 2014
Aperçu“Be proactive, not powerless! Healthy diets and frequent screening can help prevent the occurrence or reoccurrence of colorectal cancers.”
  1. ^
    "Colon Cancer: Colon Adenocarcinoma." College of American Pathologists. Web. 30 Apr. 2015. <http://www.cap.org/apps/docs/reference/myBiopsy/ColonAdenocarcinoma.pdf>
  2. ^ "Adenocarcinoma." - Cancer Types & Treatment Options. 1. Web. 30 Apr. 2015. <http://www.cancercenter.com/terms/adenocarcinoma/>.
  3. ^ "Understanding Your Pathology Report: Invasive Adenocarcinoma of the Colon." American Cancer Society. 14 Oct. 2014. Web. 30 Apr. 2015.
    <http://www.cancer.org/treatment/understandingyourdiagnosis/understandingyourpathologyreport/colonpathology/invasive-adenocarcinoma-of-the-colon>.
  4. ^ "Colon Cancer: Colon Adenocarcinoma." College of American Pathologists. Web. 30 Apr. 2015 <http://www.cap.org/apps/docs/reference/myBiopsy/ColonAdenocarcinoma.pdf>
  5. ^ Ibid.
  6. ^ "Colorectal Cancer Prevention." National Cancer Institute. 13 Feb. 2015. Web. 15 Apr. 2015. <http://www.cancer.gov/cancertopics/pdq/prevention/colorectal/Patient/page1>
  7. ^
    "Colon Cancer: Colon Adenocarcinoma." College of American Pathologists. Web. 30 Apr. 2015. <http://www.cap.org/apps/docs/reference/myBiopsy/ColonAdenocarcinoma.pdf>
  8. ^ Ibid.
  9. ^ "Crohn's & Colitis." CCFA: Bringing to Light the Risk of Colorectal Cancer among Crohn's & Ulcerative Colitis Patients. Web. 30 Apr. 2015.
    <http://www.ccfa.org/resources/risk-of-colorectal-cancer.html>.
  10. ^
    Ibid.
  11. ^
    "Colon Cancer: Colon Adenocarcinoma." College of American Pathologists. Web. 30 Apr. 2015. <http://www.cap.org/apps/docs/reference/myBiopsy/ColonAdenocarcinoma.pdf>
  12. ^
    Ostrow, J. "Chapter 98 Tests for Fecal Occult Blood." Tests for Fecal Occult Blood. U.S. National Library of Medicine, 1990. Web. 30 Apr. 2015. <http://www.ncbi.nlm.nih.gov/books/NBK445/>.
  13. ^
    "Frequently Asked Questions About Colonoscopy and Sigmoidoscopy." Frequently Asked Questions About Colonoscopy and Sigmoidoscopy. 12 June 2013. Web. 30 Apr. 2015. <http://www.cancer.org/healthy/findcancerearly/examandtestdescriptions/faq-colonoscopy-and-sigmoidoscopy>.
  14. ^
    "Treatment of Colon Cancer by Stage." Treatment of Colon Cancer by Stage. 27 Feb. 2015. Web. 30 Apr. 2015. <http://www.cancer.org/cancer/colonandrectumcancer/detailedguide/colorectal-cancer-treating-by-stage-colon>.
  15. ^ Ibid.
  16. ^
    Ibid.
  17. ^ "Leucovorin." - Chemotherapy Drugs. Web. 30 Apr. 2015. <http://chemocare.com/chemotherapy/drug-info/Leucovorin.aspx>.
  18. ^ "Definition of Fluorouracil - National Cancer Institute Drug Dictionary." National Cancer Institute. Web. 30 Apr. 2015. <http://www.cancer.gov/drugdictionary?cdrid=43130>.
  19. ^ Ibid.
  20. ^
    "DrugBank: Oxaliplatin (DB00526)." DrugBank: Oxaliplatin (DB00526). Web. 30 Apr. 2015. <http://www.drugbank.ca/drugs/DB00526>.
  21. ^ "Treatment of Colon Cancer by Stage." Treatment of Colon Cancer by Stage. 27 Feb. 2015. Web. 30 Apr. 2015. <http://www.cancer.org/cancer/colonandrectumcancer/detailedguide/colorectal-cancer-treating-by-stage-colon>.
  22. ^ Ibid.
  23. ^ "Xeloda (Capecitabine) Drug Information: Description, User Reviews, Drug Side Effects, Interactions - Prescribing Information at RxList." RxList. 20 Mar. 2015. Web. 30 Apr. 2015. <http://www.rxlist.com/xeloda-drug.htm>.
  24. ^
    Dhillon, Sohita, and Lesley Scott. "Capedtabine In Advanced Gastric or Oesophagogastric Cancer." Drugs 67.4 (2007): 601-10. Web. 30 Apr. 2015. <http://www.ncbi.nlm.nih.gov/pubmed/17352519>.
  25. ^
    Balkwill, Fran. "Inflammation and Cancer: Back to Virchow?" The Lancet. 17 Feb. 2001. Web. 25 May 2015.
    <http://www.sciencedirect.com/science/article/pii/S0140673600040460>.
  26. ^ Rakoff-Nahoum, Seth. "Why Cancer and Inflammation?" The Yale Journal of Biology and Medicine. Yale Journal of Biology and Medicine, 1 Dec. 2006. Web. 25 May 2015. <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1994795/#R4>.
  27. ^ Ibid.
  28. ^
    Hanahan, Douglas, and Robert A. Weinberg. "Hallmarks Of Cancer: The Next Generation." Cell 144.5 (2011): 646-74. Print.
  29. ^
    "Epigenetics: Fundamentals." What Is Epigenetics. Web. 25 May 2015. <http://www.whatisepigenetics.com/fundamentals/>.
  30. ^ "MLH1 Hypermethylation and BRAF Mutation Analyses, Tumor." Mayo Clinic: Mayo Medical Laboratories. Web. 25 May 2015. <http://www.mayomedicallaboratories.com/test-catalog/Clinical and Interpretive/87931>.
  31. ^
    Ibid.
  32. ^ Fleming, Matthew, Sreelakshmi Ravula, Sergei Tatishchev, and Hanlin Wang. "Colorectal Carcinoma: Pathologic Aspects." Journal of Gastrointestinal Oncology. Pioneer Bioscience Publishing Company, 1 Sept. 2012. Web. 25 May 2015. <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3418538/>.
  33. ^ "Colon Cancer: Colon Adenocarcinoma." College of American Pathologists. Web. 30 Apr. 2015. <http://www.cap.org/apps/docs/reference/myBiopsy/ColonAdenocarcinoma.pdf>
  34. ^ Ibid.