The colon and rectum, also called the large intestine, is the final part of the digestive system. The colon absorbs the liquid from food that is not used by the body and, together with some electrolytes that it receives from the small intestine, converts it into the semisolid contents that form the stool. The colon measures between 1.5 to 1.8 meters and is divided into ascending colon, transverse colon, descending colon and sigmoid colon; the last 15cm of the large intestine correspond to the rectum.
The colo-rectal wall is formed by four main layers, the mucosa, submucosa, muscularis propria and serosa. These layers can be divided into different sublayers, and all of them have diagnostic, prognostic and therapeutic implications in colorectal cancer.
What is the prevalence of colon cancer?
Colorectal cancer is the most frequently diagnosed malignant neoplasm in the general Spanish population (32,240 new cases in 2012), thus being the second most frequent neoplasm in women, after breast cancer (1400 new cases) and the third in men, after prostate and lung cancer (20000 new cases). It is estimated that this pathology will affect 1 in 20 men and 1 in 30 women before the age of 74.
This type of cancer is the second leading cause of death from cancer in Spain, second only to lung cancer. However, the risk of death has decreased in recent years, mainly due to the frequency of detection and removal of colorectal polyps, the detection of colorectal neoplasia at earlier stages and because the treatment of this neoplasia has improved in recent decades.
How can it be diagnosed?
Many cases do not present symptoms, however, discomfort may appear such as: – Tenderness and pain in the lower abdomen.
- Blood in the stool
- Frequent diarrhea or constipation or other changes in stool characteristics.
- Thin stools
- Weight loss for no apparent reason
Risk Factors
The cause of colorectal cancer is often uncertain, although it is known that there are agents or conditions that may predispose or increase the chances of developing it:
- Dietary factors: diet high in fat and low in fruits and vegetables.
- Diseases, benign or premalignant, that increase the risk of suffering it:
- Polyps in the colon or/and rectum:
- Inflammatory bowel diseases: especially Crohn’s disease and ulcerative colitis.
- Previous colorectal cancer: Having had a previous colorectal cancer increases the risk of a second colorectal cancer. For this reason, the appearance of second tumors is monitored in check-ups.
- Genetic or family factors: Up to 25% of patients have a family member who has had colorectal cancer and in less than 10% there is a hereditary component. It is important that an expert in genetic counseling assesses the patient in case of presenting several family histories of this neoplasm or family members with multiple polyps.
Colorectal cancer screening
In order to detect colorectal cancer, screening must be performed. This pathology can be diagnosed early before there is a neoplastic degeneration of its predecessors, the benign polyps. 90% of cases of colorectal cancer can be cured if they are detected early, that is, before there is any discomfort.
Eighty percent of cases that do not have a genetic component can be detected by the screening process, especially in women and men between 50 and 69 years of age. For patients with a genetic or familial risk it is necessary to perform other types of tests:
- Digital rectal examination: not valid for advanced adenomas.
- Fecal occult blood test: this test reduces mortality from colorectal cancer by 15-33% in the relative risk of annual death and by 3% in total death from colon cancer. However, it has limitations in its sensitivity and positive predictive value. One way to improve the sensitivity of this test is the immunological test, which has a lower number of false positives and is a choice in population screening. Cases that are considered positive undergo colonoscopy.
- Sigmoidoscopy: an exploration of the last 60 cm of the large intestine, where 4 out of 5 colon tumors are detected. This test reduces incidence and mortality by approximately 60%. It is necessary to perform a complete colonoscopy in case there are findings.
- Colonoscopy: it is not considered a diagnostic test, as it has significant drawbacks and there may be complications and discomfort.
Annual fecal occult blood screening and/or sigmoidoscopy is recommended every 5 years, or colonoscopy every 10 years after the age of 50. If there are pathological findings, a colonoscopy will be performed. In patients with other types of risk, the case will be studied and the most appropriate preventive treatment will be proposed.