A diagnosis of colorectal cancer depends on the stage, accuracy of the screening test or diagnostic test and symptoms of the patient.
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.
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.
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.
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.
||TNM stage criteria for colorectal cancer
||Tis N0 M0
||Tis: Tumor confined to mucosa; cancer-''in''-''situ''
||T1 N0 M0
||T1: Tumor invades submucosa
||T2 N0 M0
||T2: Tumor invades muscularis propria
||T3 N0 M0
||T3: Tumor invades subserosa or beyond (without other organs involved)
||T4 N0 M0
||T4: Tumor invades adjacent organs or perforates the visceral peritoneum
||T1-2 N1 M0
||N1: Metastasis to 1 to 3 regional lymph nodes. T1 or T2.
||T3-4 N1 M0
||N1: Metastasis to 1 to 3 regional lymph nodes. T3 or T4.
||any T, N2 M0
||N2: Metastasis to 4 or more regional lymph nodes. Any T.
||any T, any N, M1
||M1: Distant metastases present. Any T, any N.