Colorectal cancer: what are the first signs of the disease?

Published Jul 15, 2022 • By Candice Salomé

Cancers of the colon and rectum are grouped under the term colorectal, or bowel, cancer. They develop from cells that constitute the inner lining of the colon or rectum.

Colorectal cancer is the 3rd most common cancer diagnosed in the United States. It affects more than 100,000 people each year and causes more than 50,000 deaths. In more than 80% of cases, it originates from a benign tumor that evolves slowly, eventually becoming malignant.

So what are the first signs of colorectal, or bowel, cancer? How is it diagnosed? How can it be treated?

We explain it all in our article!

Colorectal cancer: what are the first signs of the disease?

What are the first signs of colorectal cancer? 

Colorectal cancer usually develops silently, without any symptoms. This stage can last for several years. When the first symptoms appear, they mainly include abdominal pain, changes in bowel habits and blood in the stool.

The abdominal pain can be more or less intense, localized or, on the contrary, diffuse. It may resemble abdominal cramps caused by bloating and does not always prompt the patient to see a healthcare professional.

Changes in bowel movements may be manifested by sudden diarrhea or a constipation that lasts for a long time. Alternating diarrhea and constipation may also be one of the symptoms. 

The presence of blood in the stool may sometimes be imperceptible. The blood is not always bright red but may be black or brown, blending in with the color of the stool.

Patients may feel constant urge to have a bowel movement and unusual sensations when passing stools. 

As the cancer progresses, a palpable mass may form in the abdomen.

Finally, the patient's general health may deteriorate and weight loss, unexplained fatigue, anemia or fever episodes may also be observed.

What are the risk factors for developing colorectal cancer? 

Several factors can contribute to the development of colorectal cancer. The risk increases when several of these factors are present.

The risk of developing colorectal cancer increases after the age of 50. The average age of diagnosis is about 70.

In addition, having already had colorectal cancer before increases the risk of developing it again.

The diagnosis of a benign polyp-like tumor of the rectum or colon also increases the risk of colorectal cancer.

Certain lifestyle habits are also known to be risk factors:

  • Unbalanced diet, high in deli meats and red meat,
  • Low-fiber diet,
  • Being overweight or obese,
  • Sedentary lifestyle,
  • Smoking,
  • Excessive alcohol consumption.

IBD (chronic inflammatory bowel disease: Crohn's disease or ulcerative colitis), especially when it extends to the entire colon and has been present for more than 10 years, requires regular colonoscopies to detect the potential onset of colorectal cancer.

Finally, it is essential to know your family health history as the risk is higher if a first-degree relative (mother, father, sister or brother) has had colorectal cancer before the age of 60. The risk is further increased if two first-degree relatives have had colorectal cancer, regardless of the age at which the cancer occurred.

How is colorectal cancer diagnosed? 

If you notice any of the symptoms described above, it is important to talk to your GP about it during your next medical appointment.

The doctor then carries out a clinical examination and, if necessary, refers the patient to a doctor specializing in gastroenterology.

In the case of rectal symptoms, the gastroenterologist can perform a rectoscopy to visualize the rectum through a rigid endoscope. This examination does not require any preparation.

Usually, the gastroenterologist also performs a colonoscopy under general anesthesia. This examination consists of introducing a flexible tube with a very small camera into the rectum and then into the colon to visualize the inner walls of the rectum and colon. If any lesions are detected, a forceps is used to take samples (biopsies) or to remove them for subsequent analysis.

>> To find out more about colonoscopy, click here to read our article <<

Anatomopathological analysis of the samples allows the doctor to confirm (or not) the diagnosis of colorectal cancer and to specify the type of lesions detected.

What is the treatment plan for people affected with colorectal cancer? 

Additional examinations 

If colorectal cancer is confirmed, a blood test will be needed to assess the patient's general health and measure the level of a tumor marker called CEA (carcinoembryonic antigen).

A further assessment will measure the extent of the cancer and determine whether it has spread to other organs:

  • In all cases: a CT scan of the chest, abdomen and pelvic region (pelvis),
  • Depending on the case:
  • An ultrasound of the abdomen and pelvis,
  • MRI of the abdomen,
  • Positron emission tomography (PET scan): this examination is based on the injection of slightly radioactive glucose into the blood. Cancer cells (which are more active than normal cells) take up and consume more glucose. As radioactivity can be detected with this technology, the examination makes it possible to obtain precise images of the areas of the body where cancer cells have spread.

This complete assessment allows the care team to decide on the treatment plan.


Treatment options are adapted to each case and discussed together with the surgeon, the radiotherapist, the oncologist and the GP.

Depending on the case, treatment may involve one or more different techniques: surgery, radiotherapy, chemotherapy and/or targeted therapies. All treatment methods are explained to the patient during a special medical appointment.  

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avatar Candice Salomé

Author: Candice Salomé, Health Writer

Candice is a content creator at Carenity and specialzes in writing health articles. She has a particular interest in the fields of women's health, well-being and sports. 

Candice holds a master's degree in... >> Learn more

Who reviewed it: Antoine Seignez, Pharmacist data science project manager

Antoine holds a PharmD and a PhD in life sciences, specializing in immunology. He studied at the University of Burgundy in France. Several of his research projects have been published in international... >> Learn more


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