Rectal Cancer: Symptoms And Warning Signs

Rectal cancer is cancer of the lower end of the colon or rectum. To understand it better, it’s helpful to understand the anatomy and physiology of the digestive system.

After eating, during the digestive process, semi-digested food passes through the stomach to the small intestine, where further digestion takes place. The residual waste matter then passes from the small intestine to the large intestine (colon). Water and salt absorption occurs in the colon until the waste matter is eventually passed into the rectum. The rectum is the final six inches of the colon. Waste matter is stored in the rectum until it is ready to be discharged from the anus.

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Are colon cancer and rectal cancer the same?

Colon cancer and rectal cancer (often referred to together as colorectal cancer) are very similar in their pathophysiology and their signs and symptoms. 

The major difference between them is the anatomy of the rectum versus the colon: while the colon is placed relatively apart from other organs, the rectum is located in the pelvis, tightly squeezed between many other important structures. 

It’s difficult to perform surgery in a small, enclosed space, so rectal cancer differs from colon cancer in its treatment.

Signs and symptoms of rectal cancer

Symptoms of rectal cancer are things that you might feel or notice yourself, while signs are things that your doctor might observe. 

If you have rectal cancer, the signs and symptoms can vary depending on the cancer stage.

Symptoms of early rectal cancer

  • A change in bowel habits, including new-onset diarrhea, constipation, or a feeling of incomplete evacuation – where the bowel does not empty completely with a bowel movement.

  • Blood in or on your stool (bowel movement) – stools that are bright red or a deep, darker red, or even black may indicate the presence of blood.

  • New onset of stool that is consistently narrower than usual.

  • Rectal or abdominal mass.

  • Rectal or abdominal pain, aches, or cramps that don’t go away.

Signs of early rectal cancer

  • Fecal occult blood – tiny amounts of blood in your stool that cannot be detected by the human eye but can be picked up by your doctor on lab analysis of a stool sample.

Symptoms of more advanced rectal cancer¹

  • Fatigue or extreme tiredness.

  • Unintended weight loss.

  • Feeling full even after a small meal. 

Signs of more advanced rectal cancer

  • Iron deficiency anemia – low red blood cell levels in your blood, detected by your doctor on a blood sample.

  • Enlarged liver – caused by a tumor that has spread to the liver and would be detected by your doctor on physical examination.

  • Jaundice – a liver condition involving the yellowing of the skin and eyes, which would be caused by rectal cancer spreading to the liver.

  • Shortness of breath may be caused by rectal cancer spreading to the lungs at an advanced stage.

  • Wasting or extremely unusual weight loss.

While the symptoms listed above can indicate rectal cancer, it is important to understand that many can also be caused by benign conditions, such as hemorrhoids (piles), irritable or inflammatory bowel disease, and gastrointestinal infection. 

Just because you have some of the symptoms doesn’t necessarily mean that you have rectal cancer. 

However, you should contact your doctor at the earliest opportunity to get screened or tested as to whether you have rectal cancer.

Rectal cancer in women

Men and women typically experience similar signs and symptoms of rectal cancer. However, in premenopausal women,² the close proximity of the uterus to the rectum and the overlap in signs and symptoms of rectal cancer and some menstrual disorders can cause confusion.

If you have ongoing lower abdominal discomfort or persistent bloating, especially if it is accompanied by unexplained weight loss, make sure to get screened for rectal cancer instead of attributing your symptoms to period pain.

Risk factors for rectal cancer

Risk factors increase your chance of getting cancer. Risk factors can be either modifiable (which means that you can do something about them, such as making lifestyle changes) or unmodifiable (you can’t change them, such as family history and genetics).

Modifiable risk factors

These are risk factors that are a result of lifestyle choices. You can reduce your risk of rectal cancer by changing your lifestyle choices.

1. Being overweight or obese

Being overweight or obese increases your risk of developing rectal cancer. This is more significant in men than women, although obesity is a risk factor for both sexes.

2. Being physically inactive

Physically inactive people have a higher risk of developing rectal cancer.

3. Smoking

Smoking increases³ your risk of rectal cancer significantly. Smoking has been linked to both colon and rectal cancer, but the link to rectal cancer is stronger than colon cancer for incidence (your chance of getting it) and mortality (your chance of dying from it).

4. Diet

Studies⁴ have shown that a high-fiber diet⁵ leads to a decreased risk of rectal cancer, while a low-fiber diet has been linked to increased risk. A diet high in processed, charred, or red meats⁶ has also been linked to an increased risk of colon cancer.

5. Alcohol 

Alcohol intake has similarly been linked with an increased risk of colorectal cancer⁷ and there seems to be a dose response: the evidence⁸ shows that risk increases with increasing alcohol consumption. 

Non-modifiable risk factors

These are risk factors that you are unable to change:

1. Age

Most incidences of rectal cancer occur in people over the age of 50. However, a family history of the disease or hereditary factors may cause it to develop in younger people.

2. Gender

Men have a slightly higher risk of developing rectal cancer than women.

3. Race

The incidence of colorectal cancer is higher in Black Americans than in non-Black Americans.⁹ Black Americans are also typically younger when diagnosed with colorectal cancer. The causes for these racial differences are unclear.

4. Hereditary colon cancer disorders

Some hereditary colon cancer disorders dramatically increase your risk of developing rectal cancer. These include Lynch syndrome and familial adenomatous polyposis.

5. History of cancer

If you’ve had rectal cancer before, you are at an increased risk of developing it again in the future, even if it was successfully treated.

6. Inflammatory bowel disease

Inflammatory bowel diseases, such as ulcerative colitis and Crohn’s disease, are known to increase your risk of rectal cancer.

7. Family history of cancer

Genetics also plays a part in your risk of developing rectal cancer. You have an increased risk if:

  • You have a first-degree relative (parent or sibling) diagnosed with rectal cancer before 50.

  • More than one of your family members has been diagnosed with rectal cancer.

  • You have a strong family history of other cancers, including endometrial, ovarian, gastric, and pancreatic cancer.

8. Previous history of radiation to the abdomen or pelvis

If you’ve had radiation therapy in that region, you are at increased risk for colorectal cancers. 

When to see your doctor

You should make an appointment to see your GP if you have any symptoms of rectal cancer. 

Your GP will examine you and determine whether you should undergo further testing. Your GP may want to send you for blood tests and/or ask you for a stool sample to test for blood in your stool.

If your GP determines that you meet the criteria for screening or suspects that there is a possibility of you having rectal cancer, they will refer you to a colorectal surgeon or colonoscopist for specialist medical advice.

Screening for rectal cancer

In the US, all people over the age of 45¹⁰ should be screened regularly for rectal cancer.

You may need to begin screening for rectal cancer earlier if you have a family history of colorectal cancer or if you have inflammatory bowel disease¹¹ or a genetic syndrome such as Lynch syndrome¹² or familial adenomatous polyposis.¹³ This is usually identified by analyzing a small sample of your feces for blood and/or cancer cells. 

If the sample is positive, you will be advised to undergo a colonoscopy, as blood in the stools can come from many sources, not just colorectal cancer.

How is rectal cancer diagnosed?


A colonoscopy is a process used in screening and diagnosis that allows your doctor to visualize the whole of your colon. 

If your doctor sees a lesion that may indicate cancer during your colonoscopy, they will take a sample of the tissue to send to the pathologist. This is called a biopsy. 

The pathologist will examine the biopsy specimen under a microscope to check for the presence of cancerous cells. A biopsy allows for a definitive diagnosis of cancer to be made.

Biomarker testing

Biomarker testing,¹⁴ also called molecular testing, may be done on a sample of your colon tissue if you are diagnosed with rectal cancer. This type of testing identifies certain proteins, genes, or markers specific to your tumor type. The results of biomarker testing can guide your doctor as to which treatment is best suited to your tumor.

Some people diagnosed with rectal cancer, especially if it has spread to other areas of the body, produce a biomarker that can be detected in the blood. This is called carcinoembryonic antigen (CEA). However, the presence of CEA should not be used to diagnose rectal cancer, as other conditions can raise it, and not all people with rectal cancer produce CEA. 

CEA is not used for diagnosis or screening, but it is a useful tool in assessing response to treatment in some people.

Other imaging

If you are diagnosed with rectal cancer, you will need to undergo further imaging to assess whether the tumor has spread beyond the rectum to other parts of the body. 

This could include magnetic resonance imaging (MRI), computed tomography screaming (CT scan), positron emission tomography (PET) scanning, x-rays, and ultrasound scanning.

The lowdown

Rectal cancer (often included under the umbrella term colorectal cancer) is cancer located at the furthest end of the colon. 

The signs and symptoms include blood in stools, changes in bowel habits, lower abdominal pain or discomfort, unexplained weight loss, and fatigue in the later stages.

Your risk for rectal cancer may be higher if you are male, over 50 years old, or Black. Obesity, smoking, and a diet low in fiber and high in processed meats may also increase your risk of rectal cancer.

Genetic factors are also linked to an increased risk of rectal cancer. If you have genetic conditions such as Lynch syndrome or familial adenomatous polyposis, a history of inflammatory bowel disease, or a family history of colorectal cancer, you have a higher chance of developing rectal cancer.

It is advised that everyone over the age of 45 should be screened for colorectal cancer, but if you show risk factors, you may need to be screened earlier.

Screening and diagnosis are usually done by colonoscopy and biopsy of the suspicious lesion.

If you notice any symptoms or meet the criteria for risk factors, it is recommended that you contact your doctor.

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We make it easy for you to participate in a clinical trial for Rectal cancer, and get access to the latest treatments not yet widely available - and be a part of finding a cure.

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