Colorectal cancer

Colorectal cancer, also known as bowel cancer, colon cancer, or rectal cancer, is when cancer develops in the colon or rectum, which are parts of the large intestine. It happens when cells in these areas grow out of control and can spread to other parts of the body. Common signs include blood in the stool, changes in bowel movements, weight loss, abdominal pain, and feeling very tired.

Most cases of colorectal cancer are linked to things like diet, obesity, smoking, and not being physically active. Eating a lot of red meat, processed meat, and alcohol can also increase the risk. Some people are more likely to get it if they have conditions like inflammatory bowel disease, such as Crohn's disease or ulcerative colitis. Rarely, certain genetic disorders can also cause it, but these are not very common.

Doctors can find colorectal cancer by looking at a sample from the colon during a sigmoidoscopy or colonoscopy. They may also use medical imaging to see if the cancer has spread. Regular screening is very important and is recommended for people between the ages of 45 and 75. During a colonoscopy, small growths called polyps can be removed if found early.

Treatment options include surgery, radiation therapy, chemotherapy, and targeted therapy. If the cancer is caught early and has not spread, surgery can often cure it. When cancer has spread widely, treatment focuses on helping the person feel better and manage symptoms. Worldwide, colorectal cancer is the third most common type of cancer, affecting millions of people each year. It occurs more often in developed countries.

Signs and symptoms

The signs and symptoms of colorectal cancer depend on where the tumor is in the bowel and if it has spread to other parts of the body (metastasis). Common warning signs include blood in the stool, changes in how often you need to go, losing weight, feeling sick, and not wanting to eat. These signs are especially important for people over 50 years old.

Bleeding from the lower part of the body or feeling very tired can also be signs of this condition. It is important to notice any changes in your usual way of going to the bathroom, like if your stool looks different or doesn’t have its normal shape.

Cause

Most cases of colorectal cancer happen in people who don’t have big genetic risks. Getting older, being male, eating lots of fat, sugar, alcohol, red meat, or processed meats, being overweight, smoking, and not exercising can raise the chances of getting this disease.

What you eat plays a big role. Drinking too much alcohol, especially more than one drink a day, can increase risk. Eating whole grains and drinking plenty of water may help lower the risk. Eating a lot of saturated fats can also raise the risk. Some bacteria in the gut, like Streptococcus gallolyticus and certain types of Escherichia coli, may also be linked to colorectal cancer. People with long-term inflammatory bowel diseases, such as ulcerative colitis or Crohn's disease, have a higher chance of developing colon cancer, especially if the disease has been around for many years or is very severe.

Having family members with colorectal cancer, especially parents or siblings, can increase risk. Some rare genetic conditions also make cancer more likely.

Pathogenesis

Colorectal cancer starts in the cells that line the colon or rectum, which are parts of the large intestine. This happens when the cells grow out of control due to changes in their genes. These changes can happen naturally or be passed down in families. One important change often involves a gene called APC, which helps control how cells grow. When APC is changed, it can lead to too much of another protein called β-catenin, which then triggers other changes that cause cancer.

As cells continue to change, they may stop responding to signals that normally tell them to stop growing. This can turn a small growth into a cancer that spreads to other parts of the body. The process usually takes many years, with cells changing step by step through a series of genetic and other alterations.

Diagnosis

Colorectal cancer is diagnosed by checking parts of the colon that seem suspicious, usually during a test called colonoscopy or sigmoidoscopy.

Sometimes, a colorectal cancer is first seen on a CT scan.

Doctors can find out if the cancer has spread by doing a CT scan of the chest, abdomen, and pelvis. Other imaging tests like PET and MRI might be used in some cases. MRI helps doctors understand how far the tumor has grown and plan the best surgery.

The details about the tumor are studied under a microscope from a small piece of tissue taken during a biopsy or surgery. The most common type of colon cancer is called adenocarcinoma.

The stage of the cancer is determined by looking at imaging and tissue results. This helps doctors understand how much the cancer has spread.

Prevention

About half of colorectal cancer cases are linked to lifestyle choices, and about a quarter could be avoided. To lower the risk, it’s important to stay active, eat a diet rich in fiber, quit smoking, and limit alcohol.

Lifestyle choices that matter include not exercising enough, smoking, drinking alcohol, and being overweight. Keeping a healthy weight through exercise and good eating habits can help. Eating lots of whole grains, fruits, and vegetables is good, but studies haven’t clearly shown that these foods alone can prevent cancer. Both alcohol and processed meats can increase the risk.

Regular physical activity is important. Exercise can lower the risk of colon cancer by about 21%, though it doesn’t affect rectal cancer as much. Sitting for long periods can increase the risk.

Screening tests can help find colorectal cancer early or even prevent it by spotting and removing growths before they become cancer. Screening usually starts between ages 50 and 75, but some places now recommend starting at 45. Different tests include colonoscopy, stool tests for hidden blood, and sigmoidoscopy. Regular screening can lower the chance of dying from colorectal cancer.

Treatment

The treatment for colorectal cancer can aim to cure the disease or help manage symptoms. The choice depends on the person’s health, preferences, and how far the cancer has spread. Early detection often allows for successful treatment through surgery.

Surgery is a key treatment, especially when the cancer is found early. It may involve removing part of the colon or rectum. For cancers that have spread, other treatments like chemotherapy or special surgeries might be used to control the disease and keep the person comfortable.

Chemotherapy, which uses medicines to fight cancer cells, is often used alongside surgery. For some types of colorectal cancer, treatments like radiation or immunotherapy may also be helpful. Support and care for emotional and physical well-being are important parts of treatment too.

Prognosis

Fewer than 600 genes are linked to how well someone does with colorectal cancer. Some genes make the outcome worse, while others make it better.

The chance of the cancer coming back after surgery depends on how far it has spread. For colon cancer, about 5% of early-stage cancers come back after five years, while about 33% of later-stage cancers do. For rectal cancer, about 9% of early cancers come back after five years, and about 34% of later-stage cancers do. These chances have gotten better over time because doctors have found new ways to treat the disease.

In Europe, less than 60% of people with colorectal cancer live for five years after being diagnosed. Getting the cancer early makes a big difference — people whose cancer is found before it spreads often live much longer than those whose cancer is found later.

Early-onset colorectal cancer

A diagnosis of colorectal cancer in people under 50 years old is called early-onset colorectal cancer (EOCC). Cases of EOCC have gone up over the last ten years, especially in people aged 20 to 40 in North America, Europe, Australia, and China.

A 2026 report found that colorectal cancer is now the biggest cause of cancer deaths for both men and women under 50 in the United States.

Incidence by age

Colorectal cancer in younger people has increased over the last decade. While better ways to find the disease may help, it is more likely due to changes in lifestyle and environment across generations.

The biggest rise in EOCC cases is happening in people aged 20 to 29, with cases going up by 7.9% each year between 2004 and 2016. People aged 30 to 39 are also seeing more cases, though not as much, at a rate of 3.4% per year during that time. Even with these increases, the number of deaths from colorectal cancer has stayed the same.

Risk factors

Risk factors for early-onset colorectal cancer are similar to those for all cases of colorectal cancer. Changes in lifestyle and environment for newer generations seem to be playing a role.

Preventive screening

In 2018, the American Cancer Society changed its screening guideline for colorectal cancer from age 50 down to age 45 because of the rise in early-onset cases. People under 60 are most likely to miss out on these important screenings.

History

Rectal cancer was found in an ancient Egyptian mummy. This person lived in the Dakhleh Oasis a long time ago during the Ptolemaic period.

Society and culture

Main article: List of people diagnosed with colorectal cancer

In the United States, March is colorectal cancer awareness month. The World Health Organization says that eating certain types of processed meat can increase the chance of getting this kind of illness.

Research

Research on early rectal cancer has not given clear answers about whether local surgery changes the chance of the cancer coming back, how long people live, or what problems might happen.

Studies from 2020 were not sure if exercises like walking, cycling, or yoga helped people with colorectal cancer with their health. Some programs might help people walk better after surgery, but it is not clear if this stops other problems. Doing exercise can make people feel better and have more energy, but it did not seem to change feelings of worry or sadness for these patients.