Colorectal Cancer Screening

For the early detection of colorectal cancer (synonyms: colorectal cancer screening, colorectal cancer prevention), diagnostic procedures described below are used. Men and women are eligible for colorectal cancer screening examinations:

  • Age of eligibility: 50-54 years – annual examination for occult (“hidden”) blood in stool.
  • Eligibility age: from ≥ 50 years for men and ≥ 55 years for women, there is an option:
    • Every 2 years examination for occult blood in the stool.
    • A maximum of 2 colonoscopies (colonoscopies), 10 years apart.

Laboratory diagnostics

Since colorectal cancer or even the intestinal polyps already lead to bleeding into the intestine, the detection of blood in the stool is an important and useful measure for colorectal cancer screening or early detection. Transport/storage: transport within 24 h, intermediate storage in the refrigerator (4 – 8 °C) up to 1 day possible.When using special collection systems, the material is stable for 5 days after sampling at room temperature.

Tests for the detection of invisible blood in stool (FOBT; Fecal Occult Blood Test)

Haemoccult test (gFOBT; Gujak-based test) [This test has been superseded by the quantitative immunologic tests].

This is an enzymatic detection method (guaiac test) that detects occult (hidden) blood in stool. This test requires prior adherence to a strict diet – a meat-free diet is required for 3 days prior to and during the test – as this test also reacts to hemoglobin of animal origin if present in the diet.Sensitivity (percentage of diseased patients in whom the disease is detected by the use of the test, i.e. The predictive value is 40-65%, i.e. in 40-65% of patients, the hemoccult test correctly detected colon carcinoma (colorectal cancer) confirmed by colonoscopy. Immunological test procedures (fecal immunochemical tests, FITs; iFOBT))

The immunological test procedures described below determine hemoglobin in the stool. They offer the advantage that they react only to human hemoglobin. They are therefore more accurate and the patient does not need to follow any special diet prior to performance.Rapid test (sandwich immunoassay)Detection of hemoglobin: sensitivity 76 %; specificity 92 %; detection limit circa 10 µg/g stoolImmunological stool test (immunoluminometric assay)Detection of hemoglobin: sensitivity 96 %; specificity > 95 %; detection limit circa 1 µg/g stoolThis test procedure detects 76-86 % of patients with colon carcinoma. A comparison of the enzymatic detection method (guaiac test) with immunological tests by scientists of the German Cancer Research Center (DKFZ) shows that immunological tests detect about twice as many of the colon carcinomas and about three times as many of the advanced precancerous lesions. Thereby, the specificity of the immunological tests was still somewhat higher than that of the enzymatic test.Hemoglobin-haptoglobin complexBecause of bleeding polyps or tumors, hemoglobin (red blood pigment) enters the intestine and thus also the stool.This hemoglobin is bound by the body to the so-called haptoglobin (a plasma protein). The hemoglobin-haptoglobin complex is formed, which can be broken down more slowly by the body than free hemoglobin.The detection of this complex in the stool is thus a special method for the early detection of gastrointestinal tumors (tumors of the stomach and intestines).Due to the later breakdown of the complex compared to free hemoglobin, bleeding from higher sections of the intestine can also be detected. The test detects 92% of patients with colorectal cancer.

Other test methods

M2-Pk colorectal cancer testThis test is able to detect a form of pyruvate kinase produced exclusively by tumor cells – inactive M2-pyruvate kinase – in the blood or stool using two specific antibodies.A special feature of the test is that not only colon carcinomas but also other tumor types can be detected on the basis of a blood sample.The specificity for the detection of a gastrointestinal tumor is given as 78 %, the sensitivity as 74-83 %. DNA test in combination with a hemoglobin immunoassayThe DNA test (manufacturer: U.S.-based Exact Sciences, Madison) includes molecular assays for KRAS mutations (methylations of the genes NDRG4 and BMP3), as well as detection of the protein beta-actin. These changes often occur in colon cancer cells (colorectal cancer cells) and its precursors before bleeding occurs, which is detected by the immunological stool tests. For safety reasons, the new test was therefore also combined with a hemoglobin immunoassay.A first study on this with almost 10,000 patients (age: 50-84 years) came to the following results: in 65 participants (0.7%), colorectal carcinoma was detected during a screening colonoscopy. The DNA test was positive in 60 of these patients, giving a sensitivity of 93.2%. The immunological test had detected only 48 carcinomas (sensitivity: 73.8%). The sensitivity of the DNA test was also better in stage I to III carcinomas, for which surgery offers a good chance of cure (93 versus 73%).An immunologic test, in combination with medical device diagnostics, allows early colorectal cancer detection and thus timely therapy.

Medical Device Diagnostics

Colonoscopy

Colonoscopy is considered the standard diagnostic procedure (gold standard). It refers to the endoscopy of the colon using an endoscope. This is a thin, flexible, tube-shaped instrument with an integrated light source. Colonoscopy is used for early detection of pathologic (pathological) changes in the intestinal mucosa (e.g., polyps, adenomas) of the entire colon and is recommended at regularly recurring intervals (see below Colonoscopy)

Endosonography

Endosonography (ultrasound examination) of the intestine, in which the transducer of the ultrasound machine is inserted into the intestine, allows direct images of the intestinal walls and adjacent structures. This allows assessment of how far a tumor has already penetrated the intestinal wall (depth of infiltration).

Virtual colonoscopy

Virtual colonoscopy (CT colonoscopy) is not currently a standard procedure for colorectal cancer diagnosis. It is a method of visualizing the entire colon by rapid multislice computed tomography.Virtual colonoscopy was developed as a possible alternative to colonoscopy with an optical endoscope. In this procedure, the colon is filled with air – as in colonoscopy. The computed tomographic image data are reconstructed into a three-dimensional internal view (3D representation), allowing the examiner to “fly” through the entire colon.

MR colonoscopy

The advantage of MR colonoscopy (magnetic resonance imaging of the colon) is the lack of radiation exposure. The procedure is still very new, so few data are available on sensitivity for advanced adenomas.

Capsule endoscopy

Capsule endoscopy is a procedure to visualize the mucosa of the digestive tract (esp. the small intestine) using a swallowable camera capsule. This procedure is the gold standard for examination of the small intestine. For examination of the colon, the data are still very limited.