Colorectal cancer (CRC), also known as bowel cancer, is the development of cancer from the colon or rectum (parts of the large intestine). A cancer is 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.
The signs and symptoms of colorectal cancer depend on the location of the 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 colorectal cancer occurs in people with little or no genetic risk. Risk factors include older age, male gender, high intake of fat, alcohol, red meat, processed meats, 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. Drinking 5 glasses of water a day is linked to a decrease in the risk of colorectal cancer and adenomatous polyps.
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 increase signaling activity. The mutations can be inherited or acquired, and most probably occur in the intestinal crypt stem cell. The most commonly mutated gene in all colorectal cancer is the APC gene, which produces the APC protein. The APC protein prevents 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 proto-oncogenes. These genes are normally important for stem cell renewal and differentiation, but when inappropriately expressed at high levels, they 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 own breakdown, or have mutations in other genes with function similar to APC such as AXIN1, AXIN2, TCF7L2, or NKD1.
Colorectal cancer diagnosis is performed by sampling of areas of the colon suspicious for possible tumor development, typically during colonoscopy or sigmoidoscopy, depending on the location of the lesion. Disease extent is usually determined by a CT scan of the chest, abdomen and pelvis. Other potential imaging tests such as PET and MRI may be used in certain cases. Colon cancer staging is done next, based on the TNM system which considers how much the initial tumor has spread, if and where lymph nodes are involved and the extent of metastatis.
The microscopic cellular characteristics of the tumor are usually reported from the analysis of tissue taken from a biopsy or surgery. A pathology report usually contains a description of cell type and grade. The most common colon cancer cell type is adenocarcinoma (98% of cases). Other, rarer types include lymphoma and squamous cell carcinoma.
TREATMENTS FOR COLON CANCER
Cancer treatment depends on the type of cancer, the stage of the cancer (how much it has spread), age, health status, and additional personal characteristics. There is no single treatment for cancer, but the most common options for colon cancer are surgery, chemotherapy, and radiation therapy.
Treatments seek to remove the cancer and/or relieve painful symptoms that the cancer is causing.
Surgery to remove part of or the entire colon is called colectomy. During colectomy, a surgeon will remove the part of the colon containing the cancer as well as the marginal area close to the cancer.
Also, nearby lymph nodes are also usually removed. Depending on the extent of the colectomy, the healthy portion of the colon will either be reattached to the rectum or attached to an opening in the wall of the abdomen called a stoma. This latter option is called a colostomy, and waste will exit the body through the stoma into a colostomy bag, instead of exiting through the rectum.
In addition to invasive surgeries like colectomy, doctors can remove some small, localized cancers using endoscopy.
Laparoscopic surgery (using several small incisions in the abdomen) may also be an option to remove larger polyps.
Palliative surgery might also be employed to relieve symptoms for cancers that are advanced or untreatable. This type of surgery will try to relieve blockage of the colon or to inhibit other conditions to relieve pain, bleeding, and other symptoms.
Chemotherapy utilizes chemicals that interfere with the cell division process - damaging proteins or DNA - so that cancer cells will become damaged and die. These treatments target any rapidly dividing cells (not necessarily just cancer cells), but normal cells can usually recover from any chemical-induced damage, while cancer cells cannot.
Chemotherapy is generally used to treat cancer that has spread or metastasized because the medicines travel throughout the entire body. Treatment occurs in cycles so the body has time to heal between doses. However, there are still common side effects such as hair loss, nausea, fatigue, and vomiting. Combination therapies often include multiple types of chemotherapy or chemotherapy combined with other treatment options.
One large-scale study has shown that daily low-dose aspirin improves the survival of patients with certain gastrointestinal cancers, such as colon cancer. While the mechanism is not well understood and aspirin's role in prevention has not been well studied, this information provides another possible adjunctive treatment option.
Radiation treatment, also known as radiotherapy, destroys cancer by focusing high-energy rays on the cancer cells. This causes damage to the molecules that make up the cancer cells and leads them to die.
Radiotherapy uses high-energy gamma-rays that are emitted from metals such as radium or high-energy x-rays. Radiotherapy can be used as a standalone treatment to shrink a tumor or destroy cancer cells; it is also used in combination with other cancer treatments.
Radiation treatments are not often used for early stage colon cancers, but may be employed if early stage rectal cancer has penetrated the wall of the rectum or traveled to nearby lymph nodes.
Side effects of radiation therapy may include mild skin changes resembling sunburn or suntan, nausea, vomiting, diarrhea, and fatigue. Patients also tend to lose their appetites and have trouble maintaining weight, but most side effects subside a few weeks after completing treatment.