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Blood in Stools and Other Symptoms of Colorectal Cancer

endoscopy centre in Singapore

The presence of blood in the stools can be alarming and distressing for most people. Suspecting that there is an underlying serious medical condition like colon cancer can lead to further anxiety in our patients. When the blood is fresh red and of large quantity, it can be even more worrisome to our patients.

Blood can originate from the upper intestinal tract (i.e., stomach or esophagus to the colon and anus). If the bleeding occurs in the upper digestive tract, stools can appear black and tarry. If bleeding originates from the lower gastrointestinal tract, the blood typically looks more red and fresher since it has not been digested.

Potential Causes of Blood in the Stools

There are several potential causes of blood in the stools. Some of the likely causes include: 

  • Piles or hemorrhoids
  • Tear in the anal lining (anal fissure)
  • Inflammatory bowel diseases (this can include Crohn’s disease or ulcerative colitis)
  • Inflammation or infection of the intestines (colitis)
  • Diverticular disease (small outpouches that form in the walls of the colon that can bleed)
  • Upper gastrointestinal tract ulcers (an open ulcer in the lining of the duodenum, stomach, or the small intestine’s upper end)
  • Esophageal varices (i.e. dilated veins in the esophagus)

If the patient has bleeding PR (bleeding per rectum), initial workup will include history as well as physical examination. Other crucial symptoms and history to note include:

  • Weight loss
  • Nature and quantity of the bleeding (Note: Bright red and fresh blood typically originates from the lower gastrointestinal tract. If the patient has colorectal cancer, blood loss may be minimal. In other cases, it is not visible to the naked eye – occult blood.)
  • Change in bowel habit (This includes the type of the stool and the frequency of the defecation. Some colorectal cancer patients can experience diarrhea or constipation).
  • Anal symptoms (This includes persistent pain or masses at the anus).
  • Incomplete emptying or the feeling like you need to pass motion, i.e tenesmus (This symptom can indicate cancer of the rectum).
  • Trauma, medical history, the use of aspirin (and other medications) and previous radiation treatment (Prior radiotherapy may lead to a condition of bleeding that can manifest many years after the treatment).
  • Family history of polyposis (i.e., familial adenomatous polyposis (FAP)) 

Concerning general examination findings include weight loss, pallor, and abdominal. 

A rectal and perianal examination may also be done. 

Additional Evaluation

To check for anemia, a full blood count might be requested. If the anemia is caused by blood loss, it typically results in iron deficiency anemia. Iron levels in the blood can be easily checked with another test, and iron supplements prescribed if indicated. If the doctor requires further evaluation, a colonoscopy with possible biopsies are done.

Colorectal Cancer

Colorectal or colon cancer is the cancer of the colon and rectum. When the food you eat enters your colon, water is absorbed and food residue will be converted into faeces (waste) by bacteria. The colon’s terminal part is the rectum. It stores waste before expelling it through the anus.

Polyps can form on the rectum and the inner walls of the colon. These benign lumps are common in people 50 years old and above. However, there are certain types of polyps that can progress into cancer and should be removed when detected. Malignant polyps typically have certain characteristics.

  • They are greater than 1 cm in diameter
  • Multiple polyps
  • Sessile polyps (i.e., those without a stalk)
  • High grade cellular abnormalities

In its early stage, the cancer cells will be confined to the colon. When undetected, it can develop and extend into the colon’s lumen. It can also spread and invade the colon wall by:

  • Entering the bloodstream (it can also travel to the liver and form secondary malignant deposits)
  • Invade neighboring organs and intestines
  • Entering the lymphatic system (it can travel into the neighboring lymph glands)

Risk Factors

Common colon cancer risk factors include:

  • Age: Women and men aged 50 years (and above) have a higher risk of colon cancer
  • Ethnicity: In Singapore, the Chinese have a greater risk for developing colon cancer
  • Personal History: Individuals diagnosed with colorectal cancer in the past or those with colorectal polyps have a higher risk of experiencing a possible recurrence. As such, regular screening is recommended.
  • Family History: Some people develop a rare condition known as familial polyposis (in similar cases, colorectal polyps can develop at an early age). These individuals have a very high chance of developing colon cancer (80 to 100%). Those with relatives with colorectal cancer or polyps also have a higher risk of developing the condition. However, it is lower compared to those people with familial polyposis.
  • Ulcerative Colitis: This disease that affects the bowels might lead to inflammation and cancer in the long term. People with ulcerative colitis are also at a higher risk of developing colon cancer.
  • Obesity and Sedentary Lifestyle: These two interrelated factors can increase one’s chance of developing colon cancer. However, physical activity has been known to reduce the risk by improving the movement of waste (feces) in the colon.
  • Dietary Habits: Research has shown that certain dietary factors can increase one’s risk of developing colorectal cancer. Some of the dietary habits include alcohol, processed and red meat, meat that are cooked at high temperature.

Despite awareness of the following risk factors, the exact cause of colon cancer is still unknown. Surprisingly, an estimated 50% of individuals with colon cancer have no known risk factors.

Screening for Colon Cancer

Screening tests can help doctors find cancer or polyps before symptoms can manifest. Early colon cancer detection has been known to improve the success rate of cancer treatment. The following screening tests may be used to detect cancer, polyps, and other abnormalities.

  • Fecal Occult Blood Test (FOBT): At times, cancer or polyps can cause bleeding. A Fecal Occult Blood Test is done to find tiny amounts of blood in the stool. If blood is found in the stools, other tests can be conducted to find the source. Colon cancer is not the only condition that can cause blood to appear in the stools. Hemorrhoids and other benign conditions can also cause these symptoms.
  • Sigmoidoscopy: A small lit tube (sigmoidoscope) is used to examine the rectum as well as the colon’s lower part. Doctors may also remove polyps that are found.
  • Colonoscopy: Using a colonoscope (a flexible and long tube with a camera), doctors can examine the insides of the colon and the intestine. Polyps that are found may also be removed during colonoscopy.
  • Computed Tomography (CT) scan of the Colon: A CT machine will be used to take images of the rectum and the colon. This is done to check for tumors and polyps.
  • Double-contrast Barium Enema: This procedure involves filling the rectum and the colon with barium (a white liquid that can enhance X-ray pictures). This will allow polyps (and anything else out of the ordinary) to be clearly seen in the scans.

Colorectal Cancer Assessment

Not all symptoms of the condition will prove the presence of cancer. The patient’s family and personal history will be looked into. A physical examination will also be done to determine the cause of the symptom(s).

If abnormalities like polyps are found, it can be removed for a biopsy during sigmoidoscopy or colonoscopy. A pathologist will examine the biopsy using a microscope and check the tissue for the presence of cancer cells.

If biopsy indicates that cancer is present, doctors will conduct additional tests to determine the cancer stage. The stage will be based on certain factors like whether the cancer has spread, whether the tumor has invaded the tissues nearby, etc.

Colorectal Cancer Stages

The stages of colorectal cancer are:

  • Stage 0: The cancer is located in the rectum or colon’s innermost lining. The cancer cells have not developed and spread (also known as pre-cancer).
  • Stage I: In this stage, the tumor has already grown into the colon or rectum’s inner wall (but not through the wall).
  • Stage II: In this stage, the tumor has grown through or deep into the colon or rectum’s wall. It may have also invaded the tissues nearby. However, the cancer cells have not spread to the lymph nodes yet.
  • Stage III: In this stage, the tumor has already spread to the lymph nodes nearby. However, the cancer cells have not spread to the other parts of the body yet.
  • Stage IV: In this stage, the cancer has spread to the other parts of the body (i.e., the lungs or the liver).
  • Recurrence: This refers to cancer that has been treated but has returned after sometime. The cancer can return in the rectum or colon or other parts of the body. 

Treatment and Care

  • Surgery. The tissues that have the tumor (including the lymph nodes and the tissue nearby) can be removed through surgery. 
  • Chemotherapy. Chemotherapy involves using drugs to destroy or shrink the cancer cells. The drugs will enter the bloodstream and travel to the cancer cells found in the body.
  • Targeted Cancer Therapy. When the cancer has spread, targeted therapy may be given. These are drugs (and other substances) that can stop or reduce the spread of cancer.
  • Radiation Therapy. Also called radiotherapy, this makes use of high-energy rays to destroy the cancer cells in the areas affected.


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