Colorectal cancer (CRC) is the cancer of the large intestine, the Distal part of the gastrointestinal tract. Almost all colonic cancers begin as small clumps of cells called Adenomatous Polyps. These polyps take several years before transforming into cancer. CRCs are 3rd most common cancer in women and 4th most common in men worldwide. There is significant Geographical variation across the world. More than half of CRC cases occur in developed countries, but CRC mortality is highest in less developed countries due to a lack of availability of health resources. In India, the incidence of these cancers is nearly 7 to 8 times less than in the affluent western world. However, in the last few decades, there has been an increase in the incidence of CRC in India.

Colon Cancer Symptoms & Signs

As such, there are no specific symptoms and signs for these cancers. However, certain symptoms raise suspicion, e.g. blood and mucus in stools, a change in bowel habits (like changes in inconsistency, difficulty in evacuation, diarrhoea or constipation), persistent abdominal discomfort like pain, cramps and unexplained weight loss, anaemia, fatigue, features of intestinal obstruction particularly in older population.

Colon Cancer Causes

1. Alteration in the genetic blueprint (DNA).
2. A diet low in fibre, high in red meat and calories, smoking, and a sedentary lifestyle with weight gain generally contribute to causing colonic cancer.
3. Age more than 50 years, African–American race, personal history of colorectal cancer or polyp.
4. Inflammatory intestine conditions like Ulcerative colitis and Crohn's disease, and other factors like diabetes and obesity.

Colon Cancer Prevention

1. Consumption of a diet high in fruits and vegetables but low in calories, red meat or processed meat.
2. Keeping alcohol and cigarette consumption low 
3. Keeping the weight on the lower side, especially avoiding putting on weight around the waist.
4. Keeping physical activity high by brisk walking and vigorous exercise.

Colon Cancer Screening

The success of any screening is dependent on the following factors:

1. The incidence of the disease should be high enough to make screening relevant.
2. It should be cost-effective.
3. It should decrease the overall mortality of the disease.
4. The population screened should be willing to take the test (convenient and less unpleasant).
5. There should be enough evidence that the potential benefits are more than the hazards of testing, diagnosis and treatment)

The CRC screening involves non-invasive stool tests and invasive colonoscopic tests in large population Organized Screening Program. The screening is done by stool test to pick up very minute quantities of blood. The standard tests are: Guaiac Fecal Occult blood test (G- FOBT) and Fecal immunochemical test (FIT). Based on the current recommendations, FIT is the first choice for detecting Fecal Occult Blood in CRC screening as no dietary restrictions are required and is a more sensitive test. Other non-invasive techniques are also available, such as Fecal DNA analysis. These tests identify molecular alterations in adenoma and Colorectal Cancer cells. However, these tests are underused due to high cost. 

Invasive tests like Sigmoidoscopy and colonoscopy after the fecal test can detect as well as remove polyps and cancers at a comparatively early stage. There has been clear evidence that screening colonoscopy decreased mortality from colonic cancers in long-term follow-up.