Colorectal cancer: when colon' cells grow out of control

Colorectal cancer (also called colon cancer or rectal cancer, depending on where it begins, though they are often grouped together because they share many characteristics) is a type of cancer that starts in the colon or rectum. These two parts make up the large intestine. Most of the large intestine consists of the colon, a muscular tube approximately 1.5 meters long, which absorbs water and salt from the remaining food after it passes through the small intestine. The waste material left after passing through the colon enters the rectum (the final 15 cm of the digestive system), where it is stored until it exits the body through the anus.

Colorectal cancer begins as a growth in the inner lining of the colon or rectum called a polyp. Some types of polyps can turn into cancer over several years, but not all polyps become cancerous. The likelihood of a polyp becoming cancer depends on its type.

The two main types of polyps are:

• Adenomatous polyps (adenomas): polyps that sometimes develop into cancer (due to this, adenomas are referred to as precancerous conditions)
• Hyperplastic polyps and inflammatory polyps: more common polyps that are generally not precancerous

Dysplasia, another precancerous condition, is an area in a polyp or the lining of the colon or rectum where cells appear abnormal (but not like true cancer cells).

About 95% of cases, colorectal cancer originates in cells that form glands producing mucus to lubricate the interior of the colon and rectum. When doctors talk about colorectal cancer, they are almost always referring to this type:

• Adenocarcinomas: a type of cancer that makes up more than 95% of colorectal cancer. These cancers begin in the cells forming mucus-producing glands inside the colon and rectum

Additionally, other less common types of tumors can also originate in the colon and rectum, such as:

• Carcinoid tumors: cancers that begin in specialized hormone-producing cells in the intestine
• Gastrointestinal stromal tumors (GISTs): tumors originating in specialized cells in the colon wall known as interstitial cells of Cajal, which are sometimes non-cancerous (benign). These tumors can be found anywhere in the digestive tract, but they are rare in the colon
• Lymphomas: cancers of immune system cells that generally begin in lymph nodes but can also start in the colon, rectum, or other organs
• Sarcomas: cancers that can begin in blood vessels, muscle layers, or other connective tissues in the walls of the colon and rectum. However, sarcomas of the colon or rectum are rare

Researchers have identified several risk factors that might increase the likelihood of developing colorectal polyps or colorectal cancer. The most significant are:

• Being older
• Personal history of colorectal polyps or colorectal cancer
• Personal history of inflammatory bowel disease (IBD)
• Family history of colorectal cancer or adenomatous polyps
• Having a hereditary syndrome
• Racial and ethnic background
• Having type 2 diabetes

Additionally, connections have been identified between diet, weight, exercise, and the risk of colorectal cancer. Most lifestyle-related risk factors associated with colorectal cancer include:

• Being overweight or obese
• Physical inactivity
• Certain types of diets
• Smoking
• Excessive alcohol consumption

Colorectal cancer might not cause symptoms initially, but if it does, most are often caused by conditions other than colorectal cancer, such as infections, hemorrhoids, or irritable bowel syndrome.

Some potential signs and symptoms may include:

• A change in bowel habits, such as diarrhea, constipation, or narrowing of the stool, lasting more than a few days
• A feeling that you need to have a bowel movement that is not relieved by doing so
• Rectal bleeding
• Blood in the stool, which may make it appear dark
• Cramping or abdominal pain
• Weakness and fatigue
• Unintentional weight loss

Colorectal cancer often bleeds into the digestive tract. While sometimes blood can be seen in the stool or cause it to appear darker, stools often appear normal. However, over time, blood loss can accumulate and lead to a low red blood cell count (anemia). Sometimes, the first sign of colorectal cancer is a blood test showing a low red blood cell count.

The survival rate for colorectal cancer is related to the stage at which the tumor is detected and its location. Tumors in the rectum tend to be more lethal than those in the colon. Furthermore, significant differences are seen between early and advanced stages. The five-year relative survival rate for stage I colorectal cancer is approximately 90%. It ranges from 80% to 50% in stage II, depending on whether it is stage IIA or IIB, respectively. A similar pattern is seen in stage III, where the five-year relative survival rate is about 80% for stage IIIA and 50% for stage IIIB. Colon cancers that have spread to other parts of the body are often more challenging to treat and tend to have a poorer prognosis. Metastatic or stage IV colon cancers have a five-year relative survival rate of about 11%. However, many treatment options are often available for people at this stage of cancer.

IMPORTANT: EARLY DIAGNOSIS OF CANCER IS CRUCIAL SINCE A CANCER DETECTED AT AN EARLY STAGE—BEFORE IT HAS GROWN SIGNIFICANTLY OR SPREAD TO OTHER PARTS OF THE BODY—HAS A GREATER CHANCE OF BEING SUCCESSFULLY TREATED. IN CONTRAST, IF THE CANCER HAS SPREAD TO OTHER ORGANS, TREATMENT BECOMES MORE DIFFICULT, AND THE SURVIVAL PROBABILITY IS MUCH LOWER.

Some techniques have been developed to diagnose colorectal cancer. These include colonoscopy and blood tests. However, these methods have limitations, such as patient stress caused by the insertion of the tube or the lack of specificity of blood tests. For these reasons, new methods are needed to improve the identification of this type of cancer.