Definition of terms
The term colon cancer refers to the uncontrolled proliferation of colon cells that have undergone malignant changes, and that are usually found at the base of an adenoma (type of polyp). Up to 90% of colon cancers are adenocarcinomas. Other relevant types include mucinous (gel-forming) carcinomas and signet ring cell carcinomas. Squamous cell carcinomas, undifferentiated carcinomas and small-cell carcinomas, on the other hand, are extremely rare. Histopathological examinations of sampled tissues have to be performed in order to identify the exact type of cancer involved. Pathologists now have a number of new methods are available that can help them to make a diagnosis (e.g. immunohistochemistry, a method that exploits the principle of antibodies binding to specific components of cells). A further important diagnostic step is to further subdivide carcinomas into different types depending on their location in the colon, i.e. whether the carcinoma is left or right-sided or whether it is located inside the rectum (rectal adenocarcinoma).
Age is the main risk factor responsible for whether a person is likely to develop colon cancer or not. In some patients, additional risk factors may include a genetic predisposition for polyp formation and a family history of polyps and colon cancer. Risk factors that further increase a patient’s risk of developing the disease include diabetes and obesity, certain inflammatory gastrointestinal disorders, a history of intestinal polyps, alcohol use, the regular consumption of red meat, smoking, and a lack of exercise.
Frequency of occurrence
Colorectal carcinomas account for approximately 15% of all colon cancers. The lifetime risk of developing a colorectal carcinoma is between 5 and 6 %, which means that out of every 100 people in the general population, between 5 and 6 will develop colon cancer. With approximately 60,000 new cases diagnosed in Germany every year, colon cancer is now the second most common type of cancer in both men and women. Patients with localized carcinomas that have not spread to surrounding tissues or organs have a 5-year survival rate (a standard measure used by physicians to compare different treatment methods and estimate a patient’s prognosis) of 100%. This gradually decreases to below 30% for patients with advanced, large-sized tumors that have spread to surrounding tissues and organs or may have spread to other parts of the body.
Just as stool tests can be used to detect colon polyps, they can also be used to detect colon cancer. However, detection rates are generally low. Other useful methods that can detect and identify colon cancers are capsule endoscopy and imaging technologies such as CT colonography and MRI-based colonography. Regardless of the method chosen, a definitive diagnosis and exact classification is only possible if tissue samples are collected for histopathological examination. As a result, it is essential that the patient undergo either conventional endoscopy or invendoscopy, i.e. procedures that will allow tissue samples to be collected. These procedures also allow the physician to use metal clips or staining agents (e.g. ink-based markers) in order to mark lesions in the colon. It is also worth pointing out that an endoscopy procedure can also be used for the resection and removal of localized tumors.
Endoscopic resectioning achieves very satisfactory treatment results in patients with localized colorectal carcinomas that have not spread beyond the mucosal layer – and thus eliminates the need for surgery. In the majority of cases, however, tumor removal will involve extended surgical resection with safe margins, as well as the removal of surrounding tissues (e.g. lymph nodes, referred to as lymph node dissection). Additional treatments may be required, such as drug-based treatments (chemotherapy, where appropriate in combination with antibody treatment) or, in the case of patients with rectal carcinomas, radiotherapy. Treatment decisions should be made on a case-by-case basis and only after thorough examination and evaluation of the patient by an experienced team of physicians (tumor board review).