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Understanding colorectal cancer

04/05/2016

Understanding colorectal cancer

With 447,000 new cases of colorectal cancer in Europe in 2012 and 215,000 deaths, colorectal cancer is a major public health issue; so much so that an entire month is devoted to its prevention in March each year. The goal of these demonstrations is to encourage women and men over 50 years or people with a particular risk of developing colorectal cancer to participate in a screening program or speak to their doctor.   While colorectal cancer is the third most commonly diagnosed cancer and the second deadliest, it can however be cured in 9 out of 10 cases if detected at an early stage.

Colon cancer and rectal cancer

Colorectal cancers include cancers that develop in the colon and rectum. Most often a benign tumor found in the colon or rectum mucosa progressively transforms into a malignant tumor. About 40% of colorectal cancers affect the rectum while 60% affect the colon.   The colon and rectum are two organs that are part of the large intestine, the last segment of our digestive tract. The colon is an extension of the small intestine located just before the rectum. The colon is divided into three parts: the ascending colon or right colon, the transverse colon and the left colon or descending colon. If all parts of the colon may be affected, colon cancer more commonly affects the left colon (70%), although right colon cancers are on the rise.   The large intestine’s main function is to absorb and concentrate residues from the digestion of food, thereby forming and storing faeces.   The rectum is the last segment of the digestive system. It connects the colon to the anal canal and provides a storing function for the excrement.

Mechanisms of colorectal cancer, the octopus to adenocarcinoma

The common point between the colon and rectum is the intestinal mucosa lining the inside wall of the intestine.   This wall is formed similar to villi pan with a zipper, lined surface cells (epithelium) which allow the extraction of nutrients from food into the blood that fuels our bodies. It is this lining that can turn cancerous tissue gradually. Colorectal cancers develop most often from a non-cancerous benign tumor, the adenomatous polyp or adenoma, which is limited to the wall of the colon or rectum.   These polyps are common and mostly harmless, but they can slowly develop into a cancerous form called adenocarcinoma. If it is difficult to estimate the time required for malignant transformation of adenoma; the average time interval would be about 9 years according to some studies. The larger the polyp, the more important the risk of cancer progression.   Adenocarcinoma is the most common form of cancer affecting the colon and rectum (95%). Cancer cells that form the cancer proliferate without control of the organization. The tumor may develop gradually in the first wall of the intestine, with cancer cells then migrating to the lymph nodes. Later they may migrate throughout the body and metastasize.   In 5% of cases, cancers affecting the colon develop from other types of cells than those at the origin of adenocarcinoma. These are rare cancers that require specific care.

Symptoms of colorectal cancer

As with many cancers, symptoms of colorectal cancer are not specific. It is a disease that remains asymptomatic and silent for a long period of time. When symptoms do appear, they are often the sign of an already advanced disease. Among the main symptoms, are the following: – abdominal pain related to the contraction of the intestine, evolving by crisis lasting two or three days and sometimes accompanied by abdominal sounds; – bowel disorders (sudden constipation or prolonged diarrhea or the alternation of the two); – the presence of blood in the stool; – anemia; – an alteration of the general state of health, unexplained weight loss and / or mild persistent fever; – for rectal cancer, rectal bleeding; – at a later stage, complications can occur such as bowel obstruction or tumor perforation; they require emergency care.

Screening

Thanks to screening and improved treatment, mortality decreases. The earlier a cancer is diagnosed, the better it can be treated, and the greater the chance of survival.

The test HEMOCCULT II® for abnormal bleeding

Until April 2015, colorectal cancer screening was essentially based on the practice of a test Hemoccult II® that identifies abnormal microscopic bleeding.

Colonoscopy

In at-risk subjects who have a personal or family history, medical care is provided early on and more frequently through colonoscopy. This medical procedure examines the colon and rectum using a probe to perform a biopsy, that is removing a small tissue sample. Colonoscopy also allows for the removal of polyps before they become cancer.

A new immunoassay

This immunoassay relies on the detection of human hemoglobin.   The latest technological advances have enabled the development of a new reliable immunoassay that is more efficient than the Hemoccult II ® test. In France, this device is available since April 2015 and made available in particular to general practitioners, as part of a colorectal cancer screening program for 50 years old to 74 years old patients. As it happens, colorectal cancer is very rare before age 50 (less 6% of cases). The test uses specific antibodies able to detect the presence of hemoglobin in the stool. It would significantly increase the number of early diagnoses and the survival rate associated with colorectal cancer.

Causes of colorectal cancer and prevention

Nowadays, the mechanisms that lead to colon and rectal cancer are known: they occur from successive mutations of genes. These genes gradually transform normal intestinal cells into cancer cells.   The modified genes become oncogenes, which enable the carcinogenesis process. Thus, people who inherit an abnormal gene or acquired a mutated gene can more easily develop colorectal cancer.   Age, heredity and health history (including inflammatory bowel diseases such as Crohn’s disease) are factors that can promote the development of colorectal cancer. As environmental factors also have an impact in the development of colorectal cancer, it is generally recommended to: prevent excess weight and obesity, – practice a regular physical activity, – keep a balanced diet by eating dietary fibre, fruits and vegetables and limit the consumption of red meat, sausage products as well as the intake of animal fats, – limit alcool consumption, – avoid smoking.

Sources: Institut National du Cancer Fondation ARC Institut Curie

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