Colorectal Cancer Diagnosis

A diagnosis of colorectal cancer depends on the stage, accuracy of the screening test or diagnostic test and symptoms of the patient.

Family history

If there are symptoms the patient is asked about a family history of bowel cancer. History of symptoms is also asked in details. Presence of local symptoms around the anus, for example indicate a rectal cancer.

Physical examination

This is followed by a physical examination known as a digital rectal examination (DRE). In a DRE the physician gently places a gloved and lubricated tip of the finger into the anus and then up the rectum. The local area is numbed using a local anesthetic gel. This is not usually a very painful examination. DRE checks for lumps in the rectum or anus. This is found in an estimated 40-80% of cases of rectal cancer.


The next step is a sigmoidoscopy. This involves insertion of a thin flexible tube with a camera on its tip for viewing the insides walls of the lower part of the large intestine on the monitor. This is called a signmoidoscope.

A sigmoidoscopy can also be used to remove small samples of suspected cancerous tissue so they can be tested in the lab. This is known as a biopsy. This may be a slightly uncomfortable test but is usually not painful. Sigmoidoscopy is performed on an outpatient basis.


A colonoscopy is an examination of all of the large intestine. This uses a longer tube and is called a colonoscope. For both sigmoidoscopy and colonoscopy bowels needs to be completely evacuated using special diets and laxatives.

As with a sigmoidoscope, the colonoscope can be used to obtain a biopsy, as well as relaying images of any abnormal regions in the walls of the large intestine. A colonoscopy usually takes about one hour to complete and is performed on an outpatient basis.


Biopsy samples from coloscopy and sigmoidoscopy are sent to the pathologist who takes microscopically thin slices of the sample and stains it on a glass slide before examining it under the microscope. This is often confirmatory for diagnosis of colorectal cancer.

Barium enema

Some set ups may also order a barium enema before signmoidoscopy or colonoscopy. This involves taking a radioopaque barium drink and an X ray of the abdomen at set periods of time thereafter. The lump shows up on X ray as the radioopaque dye passes the large intestine.

Fecal occult blood test

Colorectal cancer may also be detected on routine examination of fecal occult blood. This is called Fecal occult blood test or FBT.

Differential diagnosis

Other diagnoses that may appear similar to colorectal cancer or differential diagnosis are:

  • Diverticular disease
  • Irritable bowel syndrome
  • Inflammatory bowel disease like Crohn’s disease or ulcerative colitis
  • Hemorrhoids or piles
  • Ishcemic colitis
  • Pneumatosis coli

Further testing after diagnosis

Once diagnosis is confirmed, further testing is usually carried out for two reasons. One of them is to check the possible spread of the cancer to other parts of the body and the other is to stage the cancer to determine appropriate therapy. The tests include:

  • Routine blood tests. Liver function tests are ordered to detect possible spread to the liver. Some special blood tests are also prescribed. These check for a special protein, known as a tumour marker, released by the cancerous cells. This may be positive for some cancers. For example, elevated pre-treatment serum levels of carcinoembryonic antigen (CEA) have a negative significance interms of outcome.
  • An ultrasound scan of the abdomen to detect possible spread to liver and other organs.
  • A computerised tomography (CT) scan or magnetic resonance imaging (MRI) scan.
  • Chest X rays to detect spread to lungs.
  • Positron emission tomography (PET) is valuable for detection of recurrent colorectal cancer.

Stage and grade of the cancer

Diagnosis involves determination of the stage and grade of the cancer. This helps in determining the most appropriate therapy and also helps in estimating the possible outcome and predicting response to therapy and survival of the patient.

  • Stage 1 indicates that the cancer is still within the inner lining of the colon or rectum.
  • Stage 2 indicates that the cancer has spread into the layer of muscle surrounding the colon or rectum.
  • Stage 3 indicates that the cancer has spread to nearby lymph nodes.
  • Stage 4 indicates that the cancer has spread to another part of the body, such as the liver.

The cancer is also graded to determine its aggressiveness. Grade 1 is a cancer that grows slowly. It has least chance of spreading to other organs compared to other grades. Grade 2 is a cancer that grows moderately and has an intermediate chance of spread. Grade 3 is a cancer that grows rapidly and has a high chance of spreading to distant organs like liver, lungs etc.

AJCC stage TNM stage TNM stage criteria for colorectal cancer
Stage 0 Tis N0 M0 Tis: Tumor confined to mucosa; cancer-''in''-''situ''
Stage I T1 N0 M0 T1: Tumor invades submucosa
Stage I T2 N0 M0 T2: Tumor invades muscularis propria
Stage II-A T3 N0 M0 T3: Tumor invades subserosa or beyond (without other organs involved)
Stage II-B T4 N0 M0 T4: Tumor invades adjacent organs or perforates the visceral peritoneum
Stage III-A T1-2 N1 M0 N1: Metastasis to 1 to 3 regional lymph nodes. T1 or T2.
Stage III-B T3-4 N1 M0 N1: Metastasis to 1 to 3 regional lymph nodes. T3 or T4.
Stage III-C any T, N2 M0 N2: Metastasis to 4 or more regional lymph nodes. Any T.
Stage IV any T, any N, M1 M1: Distant metastases present. Any T, any N.

Further Reading

Last Updated: Jul 2, 2023

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Mandal, Ananya. (2023, July 02). Colorectal Cancer Diagnosis. News-Medical. Retrieved on July 15, 2024 from

  • MLA

    Mandal, Ananya. "Colorectal Cancer Diagnosis". News-Medical. 15 July 2024. <>.

  • Chicago

    Mandal, Ananya. "Colorectal Cancer Diagnosis". News-Medical. (accessed July 15, 2024).

  • Harvard

    Mandal, Ananya. 2023. Colorectal Cancer Diagnosis. News-Medical, viewed 15 July 2024,


The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
Post a new comment

While we only use edited and approved content for Azthena answers, it may on occasions provide incorrect responses. Please confirm any data provided with the related suppliers or authors. We do not provide medical advice, if you search for medical information you must always consult a medical professional before acting on any information provided.

Your questions, but not your email details will be shared with OpenAI and retained for 30 days in accordance with their privacy principles.

Please do not ask questions that use sensitive or confidential information.

Read the full Terms & Conditions.

You might also like...
Gut microbiome study challenges established cancer biomarkers, identifies new bacterial links to colorectal cancer