What is colorectal cancer screening? How to recognize colon cancer in the early stages Stages of colorectal screening - all tests, analyzes and diagnostic measures to detect colorectal cancer

Early diagnosis of colon cancer has an important prognostic value, determining the results of treatment. Timely detected colon tumorI - II stage allows you to significantly increase the five-year survival rate after surgery, i.e. achieve a radical effect - complete recovery.

The prevailing opinion that colon cancer is a death sentence at the present stage is not true. This is evidenced not only by statistical data, but also by my personal experience and the experience of my colleagues. At the same time, timely identified colon polyps with regular monitoring and removal of polyps (polypectomy) can significantly reduce the likelihood of colon cancer.

In this regard, the first and most important task of colon cancer screening is to identify risk groups who are more likely to develop cancer, i.e. so-called precancerous diseases.

The second task is to determine an algorithm for diagnostic studies that can identify colon tumors in the early stages.

Of course, colonoscopy is the most informative method for early diagnosis of colon cancer, polyps and other precancerous diseases, but as we emphasized above, there are certain difficulties and limitations for carrying out this examination on a mass scale. An important step for colon cancer screening is the development of laboratory research methods.

An ideal screening test should detect the majority of tumors without a large number of false-positive results, i.e. the method must have high sensitivity and specificity. In addition, it must be safe and accessible to patients proposed for screening.

Biochemical screening methods

For colorectal cancer, the most widely used test is the guaiac-based FBS (Haemoccult) test (a test that detects the peroxidase activity of hematin in the stool). The disadvantage of the method is that bleeding from the upper gastrointestinal tract is less likely to be detected than from the colon. False-positive results can be caused by consumption of meat, vegetables containing peroxidase, i.e. Strict dietary restrictions are necessary to confirm minimally positive results. In addition, due to the frequency of bleeding from the tumor, the sensitivity of the method is only 50 - 70%.

Enzyme immunoassay tests to detect occult blood in the stool (fecal occult blood test).

The most accessible immunochemical method for determining occult blood in feces is “ColonView Hb, Hb/Hp” test from the Finnish BioHit campaign. This is a modern method for detecting occult blood in the stool and meets all the requirements for colon cancer screening. The ColonView Hb and Hb/Hp tests for occult blood in stool are a visual immunochromatographic rapid test for the qualitative detection of human hemoglobin (Hb) and hemoglobin - haptoglobin complex (Hb/Hp) in stool samples.

• no need to follow a strict diet
• The test can be done independently at home
• high accuracy of the test (studies have shown that using the test three times increases sensitivity to 100%, and sensitivity with a single use is 96%).

However, the accuracy of the immunochemical test for detecting occult blood in the stool is much higher than other tests used for the early diagnosis of colon cancer.

The sensitivity of the ColonView Hb and Hb/Hp test is 95 - 97%, and the specificity is 96%. This is a very high indicator and sufficiently meets the requirements for colorectal cancer screening in risk groups. The accuracy of the ColonView Hb and Hb/Hp test increases when used three times. The results of the studies showed that the relative sensitivity increases as the number of sequential tests increases, and the relative specificity decreases slightly.

Table Sensitivity and specificity of the ColonView Hb and Hb/Hp test.

Carrying out colon cancer screening using the ColonView Hb and Hb/Hp test annually allows us to identify patients who need endoscopic diagnostic methods (sigmoidoscopy, colonoscopy), in addition, the combination of the test with endoscopic diagnostic methods (colonoscopy, fibrocolonoscopy) allows us to identify intestinal neoplasms in the early stages.

1. Stage - identification of risk groups with a high probability of developing colon cancer

• Intestinal bleeding with a change in the nature of stool and frequency of bowel movements (frequent, loose stools, constipation), manifested for more than 1 month (patients at any age).
• Changes in stool character (constipation, diarrhea, without intestinal bleeding, occurring for more than 1 month (patients over 60 years of age).
• Prolonged intestinal bleeding, without pronounced proctological complaints - pain in the anus, swelling, itching, burning, prolapse of hemorrhoids (patients over 60 years old)
• Detectable tumor formation in the abdominal cavity (at any age)
• Tumor formation determined by rectal examination (at any age)
• Anemia (iron deficiency) of unknown etiology
• Age over 40
• Long-term inflammatory bowel disease (IBD), ulcerative colitis (UC), Crohn's disease
• Patients with a family history of colon cancer, diffuse familial polyposis, multiple colon polyps
• Patients who have had ovarian cancer, cervical cancer, breast cancer
• Previous operations on the stomach and gall bladder (gastric resection, gastrectomy, vagotomy, cholecystectomy).

These patients require the ColonView Hb and Hb/Hp test, or an endoscopic examination of the colon (video colonoscopy, fibrocolonoscopy).

2. Stage - if the “ColonView Hb and Hb/Hp” test is positive, an endoscopic examination of the colon (video colonoscopy, fibrocolonoscopy) is mandatory.

Since up to 70% of cancerous tumors and colon polyps are detected within the sigmoid colon up to 60 cm, sigmoidoscopy and flexible sigmoidoscopy can also be used as screening.

Your health is in your hands! The annual use of the occult blood test, in particular the ColonView Hb and Hb/Hp test, for the early diagnosis of colon cancer, will allow you to avoid more serious problems in the future (at least a surgical operation, and it is not a fact that it will be radical, since the decisive role is played by the process stage from I to IV). After all, only 62% of operated patients with stage 3 colon cancer survive up to 5 years; in this regard, it is extremely important to identify the oncological process at an early stage.

By the beginning of this century, the prevention of colon cancer had become a priority in oncology. It is believed that 90% of all RTCs are preventable. Carcinogenesis in the intestine is favorable for screening, since cancer arises from adenomas within 10-15 years, and they can be removed in the early stages. It is also possible to block further progression at the adenoma level.

The goals of screening are to detect and remove adenomatous polyps and diagnose early stages of cancer. Screening has the potential to reduce morbidity. Reduced morbidity rates lead to decreased mortality. In addition, overall mortality rates will be reflected in the high proportion of early cancers that have significantly better treatment outcomes than stage III or IV cancers. Early detection of RTC among the population has 2 directions:

1. detection of RTC in high-risk groups,
2. detection of RTC in formally healthy people, without any symptoms.

The following requirements are always presented to a screening method: inexpensive, safe, easy to carry out, acceptable for subjects and testers, with high sensitivity (few false negative responses) and specificity (few false positive responses). The high-risk group includes people with a family history of cancer (1st degree relatives), patients suffering from inflammatory bowel disease for 10 years (chronic ulcerative colitis or Crohn's disease), people with severe obesity who do not engage in physical activity.

Screening for high-risk individuals begins at age 40; for others, the usual starting age for screening is 50 years. The most famous test is FOBT – determination of small amounts of occult blood in the intestinal contents. It is performed at home. 2 stool samples are taken over 3 days. It is required to follow a diet without animal proteins for 3 days before the test. The test should be repeated annually. A single examination of one stool sample is not recommended. In the US, 17.3% of the population undergoes this test.

Another method immunochemical examination of feces for occult blood– FIT– more convenient, does not require a special diet, for its production you can have a smaller number of stool samples.

The methods can reduce the risk of death from cancer by 15%; in addition, FOBT and FIT reduce the incidence of cancer by 20% due to the diagnosis of large polyps and their subsequent removal during colonoscopy.

If tests for occult blood are positive, patients should be examined with additional methods.

The second screening method is sigmoidoscopy. A sixty-centimeter endoscope allows you to visually examine the rectum and the lower part of the colon (about one third).

Sigmoidoscopy as a screening method is performed in 30% of the healthy population in the United States. If a polyp or tumor is found during this endoscopy method, a colonoscopy is then performed. The method can reduce mortality rates from RTC by 60%. Sigmoidoscopy is performed once every 5 years.

The combination of the two methods FOBT and sigmoidoscopy in the USA is performed every 5 years in 39% of those examined during screening. The combination of methods can reduce the risk of mortality from RTC by 80%.

Colonoscopy among screening methods in some countries it is designated as the gold standard. A colonoscope allows you to examine the entire colon and remove detected polyps. Periodic colonoscopies can prevent the development of cancer in 76-90% of patients with large polyps.

Colonoscopy in a healthy population is performed once every 10 years, and in patients with small polyps or solitary adenomas without severe dysplasia - once every 3 years. In patients with chronic peptic ulcers, colonoscopy is performed at intervals of 1-2 years.

Among the recently developed and very promising screening and diagnostic methods are: virtual colonoscopy– spiral computed tomography with very thin sections and 3 measurement diameters. The method avoids the painful bowel preparation required for conventional colonoscopy. The sensitivity of the new method for diagnosing polyps larger than 1 cm is 90%, and the specificity is 96%. The method allows you to detect adenomas larger than 6 mm in the entire colon. The duration of the study is 10 minutes. False positive and false negative results are extremely rare.

Double X-ray contrast method of the colon left in screening programs due to non-diagnosis of small polyps, a large number of false-positive conclusions, high cost, and difficulties in preparing for the study.

Of the new screening methods (still experimental), we note stool DNA test. The desquamated epithelium of the colon is isolated from stool, DNA is extracted and its mutation analysis is performed.

Based on materials from the monograph by A.M. Garin and I.S. Bazin
"The Ten Most Common Malignant Tumors"

The effectiveness of screening using the fecal occult blood test has been confirmed in several specific studies.

For example, a study conducted in Minnesota (USA), which included 48,000 people, showed that annual stool occult blood testing reduces colon cancer deaths by 33%. In the group in which screening was carried out once every 2 years, mortality decreased by 21%.

Long-term observation over 18 years revealed a decrease in the incidence of colon cancer in the experimental groups. The incidence decreased by 20% and 17% in the groups that were screened annually and every 2 years, respectively.

It should be noted that to confirm the diagnosis, 80% of test-positive patients underwent colonoscopy, sigmoidoscopy or double contrast radiography.

In a study conducted in Finland, 62,000 people were divided into control and experimental groups. Participants in the last group were tested for occult blood once every 2 years for 13 years. After ten years, mortality from colon cancer decreased in the experimental group by 18%.

Studies have shown that on average 1-5% of people test positive for occult blood, of which 2-10% are diagnosed with cancer, and 20-30% are diagnosed with adenomatous polyps of the colon.

Sigmoidoscopy

There are no studies-based data on the effectiveness of sigmoidoscopy for colon cancer screening. However, empirical studies indicate that sigmoidoscopy is likely to reduce mortality from colon cancer. Two studies showed that the risk of death from distal colorectal cancer was statistically significantly reduced (by 70-90%) in people who had 1 or more sigmoidoscopy examinations.

A multicenter study conducted in Utah (USA) showed a statistically significant (44–47%) reduction in mortality from colon cancer among the population in which sigmoidoscopy screening was performed.

It should be noted that the detection of an adenomatous polyp or cancer in the sigmoid or rectum served as an indication for colonoscopy.

These studies suggest that regular sigmoidoscopic screening of people over the age of 50 years is likely to lead to a reduction in mortality from distal (lower) colon cancer.

There are no data on the effectiveness of colonoscopy and contrast-enhanced radiography for colon cancer screening. However, studies are currently being conducted, the preliminary results of which indicate the superiority of colonoscopic screening over sigmoidoscopy.

In a study of 3,120 military veterans over 60 years of age, mostly men (97%), 10.5% had colonoscopies that detected adenomatous polyps greater than 10 mm in diameter, adenomatous polyps with severe dysplasia, villous tumors, and cancer.

The likelihood of detecting benign and malignant tumors in the proximal (upper) colon was statistically significantly higher in individuals who were diagnosed with tumors in the distal (lower) colon. However, half of the patients who had certain tumor formations in the proximal colon did not have tumors in the sigmoid and rectum.

As a result of colonoscopy screening, 5.6% of Americans over the age of 50 years were diagnosed with benign and malignant colon tumors. It is important to note that in 46% of people who had some type of mass in the proximal colon, the sigmoid colon and rectum were not affected.

Using colonoscopy to screen for colon cancer only in people whose sigmoidoscopy reveals tumors in the distal colon will result in about half of all tumors located in the proximal colon not being detected.

This fact calls into question the advisability of using sigmoidoscopy for colon cancer screening.

The use of a combination of two methods: sigmoidoscopy and occult blood test led to only a small and statistically insignificant improvement in the detection of colon tumors.

Early detection or screening ( from English. screening - screening) rectal cancer is carried out during preventive examinations of the population using a hemoccult test and endoscopic research methods.

Spotty discharge is one of the leading symptoms of rectal cancer. They are observed in 70-90% of patients. A hemoccult test is an examination of stool for occult blood. The meaning of the method is the study of numerous contingents (production teams, residents of certain areas of cities, etc.). The test is given in envelopes, which must be returned to the researchers. The test is carried out by the person being examined. If the results are positive or questionable, sigmoidoscopy and fibrocolonoscopy are performed. Cancer and polyps are diagnosed with positive tests in up to 68% of cases

Another area of ​​screening and early diagnosis of rectal cancer is the study of tumor markers. The study of the concentration of carcinoembryonic antigen (CEA) in blood plasma has been used since 1965. CEA is a protein that is normally found in the epithelial cells of the digestive tract, mammary glands and bronchi. In healthy people, its concentration is about 0-5 μg/l. Borderline values ​​are 5-8 µg/l, Pathological values ​​are more than 8 µg/l. For rectal polyps, CEA reaches 14 mcg/l. At stages 1-2 of cancer, 27 µg/l, at stage 4 - 193 µg/l.

For early diagnosis and screening of colorectal cancer, great hopes are placed on advances in molecular medicine. The principle is based on identifying molecular tumor markers in the feces of the studied populations. These are tumor DNA molecules that have gene mutations, determined by appropriate laboratory techniques. Such methods are still very expensive. In addition, there are molecular markers of tumor sensitivity or resistance to chemotherapy.

Examination of patients with diseases of the colon, anal canal and perineum should begin with clarification of complaints, history taking and general examination. A general clinical examination is of great importance for establishing a diagnosis and serves as the basis for the selection of special methods for examining the colon.

The leading diagnostic methods in this case are examination and palpation of the abdomen, examination and palpation of the perineum, groin areas, digital examination of the rectum, anoscopy, sigmoidoscopy.

A digital examination of the rectum is performed in the knee-elbow position or lying on a proctology chair. If a deeper digital examination of the rectum is necessary, it is enough for the patient to straighten his torso from the knee-elbow position and then “sit down” on the examiner’s finger inserted into the rectum. When the patient strains, the upper parts of the rectum seem to be pressed onto a finger. This technique successfully replaces the squatting position, which is uncomfortable for the doctor and unstable for the patient.

Most often in proctological practice, the patient is positioned on his back in a proctological chair with the limbs moderately adducted to the abdomen, located on footrests. This position is most convenient not only for a detailed examination of the perineum, anus and digital examination of the rectum, but also for performing anoscopy and examination with a rectal speculum.

First of all, pay attention to the condition of the skin around the anus, the inner surfaces of the buttocks and the sacrococcygeal region.

For the purpose of unified registration of the topography of pathological changes identified during examination of the anus and perineum, it is customary to use a clock dial diagram.

Sigmoidoscopy. Rigid sigmoidoscopy allows you to visually assess the inner surface of the rectum and distal third of the sigmoid colon to a level of 20-25 cm from the anus.

There are practically no contraindications to examining the intestine through a sigmoidoscope. However, in some conditions and diseases (profuse bleeding from the intestine, narrowing of its lumen of a congenital or acquired nature, acute inflammatory diseases of the anal canal and abdominal cavity, acute fissure of the anal canal), the examination should be postponed for a while or performed with great care in gentle positions for the patient or after pain relief.

When performing sigmoidoscopy, the color, shine, moisture, elasticity and relief of the mucous membrane, the nature of its folding, and features of the vascular pattern are assessed; the presence of pathological formations; as well as the tone and motor function of the examined sections.

Anoscopy with a rectal speculum. Examination of the anal canal using a rectal speculum is the most unpleasant procedure for patients. It is necessary to limit the use of a rectal speculum to the anal canal. Inspection of each wall of the anal canal is carried out by alternately inserting the viewing part of the instrument into the intestinal lumen.

Biopsy. Intravital pathomorphological study of rectal tumors is important for recognizing the nature of neoplasms. Microscopic confirmation of the diagnosis of cancer is necessary to avoid unnecessary operations for inflammatory diseases and benign tumors. Histological examination of tumor tissue determines its structure and degree of differentiation of cellular elements, which allows you to correctly select the scope of surgical intervention.

A biopsy is usually performed during sigmoidoscopy. They use various instruments that make up the endoscopic coloproctology set. In some cases, it is important to obtain tissue at the border of the lesion. To study a malignant tumor, tissue is taken from its edge at the border with the unchanged mucous membrane. When biopsying the mucous membrane, those areas that protrude into the intestinal lumen are selected. The resulting piece of tissue is fixed in a 10% solution of neutral formalin. It should be remembered that a biopsy is a surgical procedure that requires careful execution, control of hemostasis and appropriate documentation.

Typically, bleeding from the bed of the removed tumor site or mucous membrane is small and stops on its own. If bleeding is more intense, it must be stopped by pressing a gauze ball, which is advisable to moisten with a solution of hydrogen peroxide, adrenaline, aminocaproic acid, or use electrocoagulation.

Cytodiagnosis, a cytological examination of discharge from the inner surface of the intestine, is inferior in its information content to the histological method, but in coloproctological practice the method acquires particular value if it is impossible to perform a biopsy. In order to quickly clarify a malignant lesion, cytodiagnosis can provide invaluable assistance. In this sense, the method should be used both in inpatient and, especially, outpatient settings.

Material for cytodiagnostics is usually collected through a sigmoidoscope. Using a small gauze or foam ball on a long instrument inserted into the intestinal lumen through the tube of the device, the discharge is taken and transferred to a fat-free glass slide for subsequent study.

X-ray diagnostics.X-ray examination of the colon. An important place in the examination of a proctological patient is occupied by the study of the condition of the entire colon. The most accessible and widespread way to study the final part of the digestive tract is the x-ray method. Irrigoscopy is of greatest diagnostic value. It is with this that it is necessary to begin an X-ray examination of the colon.

This method has search, diagnostic and differential diagnostic value. During irrigoscopy, the following techniques must be used: tight filling of the intestine, studying the relief of the mucous membrane after emptying the intestine from the contrast mass, double contrasting.

Colonoscopy- an important method for diagnosing colon diseases. It is performed using special devices - colonoscopes, of which there are currently quite a few different models. In many countries, this study is performed by coloproctologists; in Russia there is a special specialty - an endoscopist, which makes the use of colonoscopy even more informative. Colonoscopy, which has devices for photographing, performing biopsies and removing various pathological neoplasms, is a method for clarifying the diagnosis of diseases of the entire colon - from the cecum to the rectum. Every coloproctological patient should undergo a colonoscopy for rectal polyps, and even more so for cancer of the distal colon detected during sigmoidoscopy, it is necessary to examine the entire colon; so as not to miss synchronous tumor or inflammatory changes located above the level achievable by a rigid proctoscope. You should know that barium enema (irrigoscopy) and colonoscopy do not compete, but complement each other. Colonoscopy is indispensable for follow-up of patients after removal of polyps, and for regular examinations of the colon in patients undergoing surgery for colon cancer.

Ultrasound examination (ultrasound) - a method for diagnosing rectal cancer, its prevalence, metastases to other organs of the abdominal cavity, as well as determining the degree of invasion of a colon tumor into the wall of this organ and for detecting affected regional lymph nodes. The high degree of agreement between ultrasound data and postoperative examination of removed specimens indicates the wide capabilities of this technique.

Laboratory diagnostics- general blood and urine tests, biochemical tests.

Laparoscopy. To diagnose liver metastases, detect abdominal carcinomatosis.

Examination of the urinary tract and genitals to exclude tumor growth in the vagina, bladder, or prostate gland.

Seems to be an extremely good candidate for screening. The prognosis after treatment is much better in the early stage of the disease, and the polyp-carcinoma sequence is proposed as an opportunity for cancer prevention by treating precancerous disease. An ideal screening test should detect the majority of tumors without a large number of false-positive results, i.e. the method must have high sensitivity and specificity. In addition, it must be safe and acceptable in the population being proposed for screening.

For colon cancer, the most widely used method is the guaiac acid-based fecal occult blood test (a test that detects the peroxidase-like activity of hematin in the stool). Because this activity is determined by the amount of hemoglobin passing through the gastrointestinal tract, upper bleeds will be less likely to be detected than colonic bleeds. On the other hand, false-positive results may be caused by consumption of animal hemoglobin or vegetables containing peroxidase, and dietary restrictions are necessary to confirm minimally positive results. In addition, due to the periodic nature of bleeding from the tumor, the sensitivity of the method is only 50-70%.

Tumors found in colon cancer screening are more likely to be at an early stage than those that are already symptomatic, but this does not prove that screening is beneficial. Even improvements in survival for patients whose tumors are detected by screening are inconclusive because screening is inherently biased. These errors have three components - selection, duration and delay.

Selection bias arises from the tendency of people who agree to be screened to perceive themselves as being extremely healthy, so that the atypical population is perceived as a whole. Duration errors show the tendency of colon cancer screening to detect a disproportionate number of slow-growing cancers that therefore have a good prognosis. Lag bias arises from the time between the time the cancer is detected by screening and the time the diagnosis is made in a patient who has not been screened for colon cancer. Because survival is measured from the time of diagnosis, colon cancer screening advances the time of diagnosis so that survival time is prolonged without necessarily changing the time of death.

Because of these biases, effectiveness can only be assessed by comparing disease mortality in a population screened for colon cancer with an identical population not screened. This has been done in the form of well-designed randomized controlled trials, and for colorectal cancer, three studies using fecal occult blood testing reported mortality data.

The first was conducted in Minnesota and showed a significant 33% reduction in the association with annual fecal occult blood testing and a significant 21% reduction in the biennial screening group. However, this study was conducted on volunteers, so it is not a true population study. In addition, the assay used rehydrated Haemoccult, which is not very specific, resulting in a large number of patients tested negative.

The Nottingham randomized trial included 150,251 people aged 45–74 years and was conducted from 1981 to 1991. At the first stage, the analysis was sent to 75,253 patients, of which 53.4% ​​completed it. The test was positive in 906 (2.1%), and of these, 104 (11%) were found to have carcinoma (46%, level of evidence A). Those who completed the analysis were offered additional screening at 2-year intervals, and an additional 132 cases of cancer were detected (37%, level of evidence A). A total of 893 cancers were diagnosed in the study group, of which 26% were detected through colon cancer screening, 28% developed over time, and 46% occurred in patients who declined the test. After a mean follow-up of 7.8 years, 360 patients in the study group died of colon cancer (compared with 420 in the control group). This shows a significant (15%) reduction in cumulative mortality (odds ratio 0.85, 95% confidence interval 0.74-0.98). An almost identical study was conducted in Funen, Denmark, and showed extremely similar results - an 18% reduction in mortality. While there is little doubt that colon cancer screening based on stool occult blood testing can reduce colon cancer mortality, although not significantly when performed in the general population, there is a need to increase compliance and improve the sensitivity and specificity of the screening method in the future.

Because 70% of cancers and large adenomas are found within the distal 60 cm of the colon, flexible sigmoidoscopy has been proposed as a screening method. There is also convincing evidence that it is a more sensitive method than stool occult blood testing. In a multicentre randomized trial, the Imperial Cancer Research Fund (UK) investigated the use of flexible sigmoidoscopy as a screening method, but the correlation between the method and mortality is still unknown. Another approach to improve screening is to test stool for DNA mutations known to occur in colon cancer. This would be highly specific, but the assay would need to be able to detect mutations in a number of genes because there is no single genetic mutation that is common to all cancers. However, researchers have been able to identify mutations in the APC, p53 genes in stool samples obtained from patients with colon cancer, so studies of several relevant genetic mutations in a stool sample are not entirely impossible.

SURVEILLANCE IN HIGH RISK GROUPS

Patients at high risk for colon cancer are not suitable for the population-based colon cancer screening strategies described above because the tests lack sensitivity. However, another important group, including patients with adenomatous polyps, significantly challenges the use of colonoscopy. Based on these reasons, it is recommended to classify patients as having a low, moderate, or high risk of adenoma recurrence. In the low-risk category (those who have one or two adenomas less than 1 cm in diameter), follow-up is not recommended or colonoscopy is recommended every 5 years; in the average risk group (3-4 adenomas more than 1 cm in diameter) - colonoscopy every 3 years; in the high-risk group (5 or more small adenomas or 3 or more, at least one of which is more than 1 cm in diameter), patients should undergo colonoscopy after a year. While these recommendations are currently based on less than compelling evidence, they represent a very prudent approach and are widely accepted in the UK.