What tests should patients with colorectal cancer take?

Do you know something about colorectal cancer? Do you know what kind of examinations and health care should be done for colorectal cancer? Let's learn some knowledge about colorectal cancer.

1. Fecal occult blood test The fecal occult blood test is one of the means of early detection of colorectal cancer. Since colorectal cancer often presents different degrees of bleeding due to mucosal erosion and ulceration, a simple and easy fecal occult blood test can be used to monitor colorectal cancer. The early fecal occult blood test was a chemical coloring method, and the commonly used reagents were benzidine or guaiac, etc., which have gradually been replaced by more specific immune occult blood reagents in recent years. However, since the fecal occult blood test cannot distinguish between cancerous and non-cancerous bleeding, it is currently mostly used as a preliminary screening method for large-scale population colorectal cancer census. However, a small number of early cancers may also present false negative results and lead to missed diagnosis. According to statistics, 50% to 60% of colorectal cancer patients and 30% of colorectal polyp patients have positive fecal occult blood tests. The fecal occult blood test is a non-specific diagnostic method, and any situation that causes gastrointestinal bleeding can lead to a positive fecal occult blood test. However, as a simple and rapid method, the fecal occult blood test can detect patients with suspected colorectal cancer from "healthy" people and high-risk groups, providing a high-risk target population for further examination. Therefore, the fecal occult blood test is still the most commonly used method for colorectal cancer screening. The surface of colon cancer is prone to bleeding. The general fecal occult blood test can be "positive" as long as there is about 2ml of bleeding in the digestive tract. Hardcastle reported that the fecal occult blood test was used to screen for colorectal cancer in asymptomatic people, and those who were positive were further examined by fiber colonoscopy. As a result, 2/3 of the colorectal cancer patients found in the survey group were detected by positive fecal occult blood test, but 1/3 of the cases were missed due to negative occult blood test and were found after symptoms appeared in the future. In the literature, 65% to 75% of adenomas detected by colonoscopy were negative for fecal occult blood test, and 38% to 50% of colorectal cancers detected were negative for fecal occult blood test. It can be seen that a negative fecal occult blood test cannot exclude the possibility of colorectal adenoma or cancer. When Hardcastle screened asymptomatic people with fecal occult blood tests, 2% of them tested positive for occult blood. Among those who tested positive, 10% were found to have colorectal cancer after further colonoscopy and other examinations. It can be seen that the detection rate of colorectal cancer in people with positive fecal occult blood tests in Europe and the United States is quite high. Therefore, European and American clinicians attach great importance to those with positive fecal occult blood tests and perform colonoscopy examinations. In most areas of my country, because gastric cancer is far more common than colorectal cancer (about 3:1), clinicians often perform gastroscopy or GI examinations repeatedly for those with positive fecal occult blood tests, but ignore the necessity of colonoscopy, which often leads to delays in the diagnosis of colorectal cancer. Several well-known international surveys have shown that screening with fecal occult blood tests can reduce the mortality rate of colorectal cancer by 15% to 43% (Table 1).

2. Carcinoembryonic antigen (CEA) test CEA does not have specific diagnostic value, and there are both false positives and false negatives. The positive rate of early patients is low, and 50% of patients with lymph node metastasis have CEA higher than normal. Therefore, it is not suitable for general screening or early diagnosis. However, it is helpful in estimating the prognosis of colorectal cancer and diagnosing postoperative recurrence. Zeng et al. from the New York Memorial Hospital in the United States reported that 114 patients with colorectal cancer with lymph node metastasis had serum CEA <5ng/ml before surgery, and 32 cases recurred after radical resection, of which 44% of patients had CEA increased to more than 5ng/ml at the time of recurrence. The serum CEA of patients with distant metastasis is much higher than that of local recurrence. Clinical data from the Affiliated Tumor Hospital of Fudan University show that although a considerable number of patients (including stage III and even some stage IV patients) have normal CEA tests before surgery, once CEA is found to be continuously elevated during postoperative follow-up, more than 90% of them are related to tumor recurrence and metastasis. Sometimes CEA elevation may occur 5 to 7 months before clinical symptoms occur, so CEA detection during follow-up is very necessary. Similar detection indicators include CA50, CA19-9, CA72-4, CA242, etc. Generally, these indicators should be checked at the same time, because patients may have abnormalities in several items at the same time, or only one item may be abnormal. For this reason, some people advocate that if CEA and other indicators are found to be continuously elevated during follow-up, laparotomy can be performed to improve the resection rate and cure rate of recurrence. Most patients with colorectal cancer often have elevated serum CEA levels, exceeding 50μg/ml. However, the specificity of this test is not strong, and serum levels may also be elevated in some non-digestive tract tumors and benign lesions. In addition, CEA has poor sensitivity to early colon cancer and adenomatous polyps, so its use in early colorectal cancer detection is not effective. In 1982, Magagi et al. used CA19-9 prepared by immunizing mice with human colon cancer cell lines to identify highly cancer-specific salivary gangliosides, and found that 19% to 49% of colorectal tumors had elevated levels. However, it is more sensitive to the gastric, pancreatic, hepatic and bile ducts, and as a serological test for colorectal cancer, it is not more sensitive than CEA.

Other tests, such as the detection of colorectal cancer-related antigens, determination of ornithine decarboxylase and serum sialic acid content, and leukocyte adhesion inhibition test, have shown certain effects in studies, but their specificity and sensitivity need to be further improved for clinical application.

3. Cytological and histological diagnosis Pathological diagnosis is the basis for clarifying the diagnosis and formulating treatment plans, including exfoliative cytological examination and pathological examination of biopsy tissue specimens.

Intestinal exfoliative cytology has a high specificity for the diagnosis of malignant tumors. Since 1010 epithelial cells are shed every 24 hours in normal intestinal mucosa, and the renewal rate of tumor epithelial cells is faster, about 1% of tumor cells are shed into the feces and excreted from the body. Therefore, collecting these exfoliated epithelial cells is of great significance for judging the nature of colorectal lesions. The methods include rectal irrigation, brushing under direct vision of colonoscopy, wire mesh balloon wiping, and finger smear method of lesion. After Papanicolaou staining, light microscopy is performed. The discovery of malignant cells is of diagnostic significance. If it is suspected to be malignant or the nucleus is slightly enlarged and the chromatin is increased, it is not enough to make a final diagnosis, suggesting that a reexamination or biopsy should be performed for confirmation. It has been reported that the sensitivity of exfoliative cytology examination is 93% and the specificity can reach 100%. In recent years, molecular biology technology has provided a broad prospect for pathological diagnosis. The application of amplification of trace tissue specimens, in situ hybridization technology or Southern blotting is expected to provide feasible molecular detection methods for identifying colorectal precancerous lesions and early detection of colorectal cancer. For example, the combination of intestinal exfoliative cytology examination methods and molecular biology techniques such as K-ras gene mutations and abnormal expression of CD44 genes in exfoliated cells may be of certain significance for the detection of early colorectal cancer or precancerous lesions.

Biopsy tissue pathological examination is the most ideal method for tumor diagnosis. For smaller tumors, the entire tumor should be removed as much as possible for examination, including the pedicle (if there is no obvious tumor pedicle, the mucosa at the base of the tumor should be removed for examination). When performing a biopsy on a larger tumor, care should be taken to avoid clamping necrotic tissue on the surface of the tumor. If possible, try to clamp the tissue at the junction of the tumor base and normal mucosa. When adenoma is suspected of canceration, it is advisable to take samples from multiple locations.

4. Genetic examination In the past 10 years, molecular genetics has revealed many genes related to tumorigenesis, and people have paid more and more attention to and understood the relationship between molecular genetics and tumorigenesis. For example, hereditary non-polyposis colon cancer (HNPCC) is an autosomal hereditary disease. 80% to 85% of patients may develop colorectal cancer in young and middle-aged people, and some may also develop malignant tumors in other organs. In this family, 5 DNA mismatch repair genes (hMSH2, hMLH1, hPMS1, hPMS2, hMSH6) are known to have a high mutation rate (60% to 70%). Detecting mismatch repair genes in high-risk family members has a certain effect on predicting the occurrence of colorectal cancer. In addition, other related studies such as gene sequencing have also provided more promising methods for the diagnosis of high-risk groups of colorectal cancer with genetic predisposition.

5. Rectal mucus T antigen test, also known as galactose oxidase test, is a simple method to detect specific markers of colorectal cancer and precancerous lesions. As long as the liquid on the rectal finger cot is smeared on a special paper film or glass slide, the galactose oxidase reaction and Schiff's reagent color development can be used to determine whether the patient's intestinal mucosa has T antigen expression. Clinical and general surveys have verified that this method has high sensitivity and specificity for the detection of colorectal cancer. Its use in general surveys has a complementary effect with the immune occult blood test for colorectal cancer screening, but there are also certain false positive and false negative rates.

1. Rectal digital examination can at least palpate the rectal wall within 7 to 8 cm from the anus. During the examination, the examinee can take different positions according to the needs of the examination, such as lateral position with lower limbs flexed, supine lithotomy position, chest-knee position and squatting position. The examiner inserts all index fingers into the rectum and touches the left, right, front and back with the fingertips in turn. Early rectal cancer may appear as small polypoid lesions that are higher than the mucosa. Careful touch must be made during digital examination to avoid missed diagnosis. Large lesions are easy to touch, appearing as exogenous masses of varying sizes, or as invasive strictures. Touching must be gentle during rectal digital examination, and squeezing must be avoided to avoid causing cancer cells to enter the bloodstream and spread. During digital examination, attention should be paid to determining the size of the tumor, the range of the intestinal wall circumference, whether it is pedunculated or broad-based, the distance from the lower edge of the tumor base to the anal margin, the infiltration of the tumor into the intestine (whether it involves the vagina and prostate, and whether it is fixed to the pelvic wall), and the texture of the tumor. In addition, patients with colon cancer should also undergo a rectal digital examination or a rectal-vaginal bimanual examination to determine whether there are implants in the bladder-rectal fossa or uterine-rectal fossa.

2. Sigmoidoscopy Hard tube sigmoidoscope can generally be examined to a depth of 20 cm from the anus, which is the simplest and most feasible method for examining the low colon within 20 cm from the anus. However, due to the distribution of colorectal cancer, the proportion of high-position colorectal cancer increases with age, so sigmoidoscopy for these patients is not comprehensive enough. Due to its good bending, the 60cm fiber sigmoidoscope can not only peek into the rectum and sigmoid colon, but also some can reach the descending colon and even the splenic flexure colon. If the fiber sigmoidoscope is inserted into the splenic flexure colon, 73% of colorectal cancer can be detected. From the perspective of clinical application, the sensitivity of fiber sigmoidoscopy in detecting colorectal cancer is 50% to 60%, while that of hard tube sigmoidoscope is 25% to 33%. The cancer detection rate of sigmoidoscope is 2 times higher than that of hard tube sigmoidoscope, and the adenoma detection rate is 6 times or 2.5 to 3 times higher.

Sigmoidoscopy is also a screening tool with a high screening efficiency. Studies have found that it can not only detect most colorectal tumors, but also predict proximal colorectal lesions. According to statistics, 30% of patients with colorectal cancer or adenoma proximal to the splenic flexure have lesions in the distal colon. Therefore, once a distal colorectal tumor is found by sigmoidoscopy, a full colon examination should be performed with a colonoscopy. Domestic scholars used fiber sigmoidoscopy to screen 4,299 people at high risk of colorectal cancer, and detected 16 cases of colorectal cancer, with a detection rate of 506/100,000, which is 29 times the incidence rate of the local natural population. However, since sigmoidoscopy is also a traumatic examination, its bleeding and perforation rates can reach 1/10,000 to 2/10,000. Therefore, when it is used as a screening tool, high-risk groups are often selected for examination, such as those with positive fecal occult blood tests, or those who meet other high-risk conditions.

3. Double contrast barium enema It is not easy to find lesions with a diameter of less than 2 cm in general barium enema examination, but experienced examiners can find colon cancer with a diameter of less than 1 cm using low tension double contrast barium enema. For patients with clinically suspected symptoms of low-lying colorectal cancer, rectal digital examination and hard tube sigmoidoscopy should be used first, because these two methods are more reliable than barium enema for colorectal cancer within 20 cm from the anus. Double contrast barium enema can detect 92% of colorectal cancer, of which the detection rate of Dukes A stage cancer is 55% to 85%. The detection rate of polyps over 1 cm is 70% to 90%, and the detection rate of polyps below 1 cm is 50% to 80%. However, it has been reported that the barium enema misdiagnosis rate for polyps with a diameter of less than 1 cm can be as high as 54%, and 25% of polyps with a diameter of more than 2 cm are also missed during barium enema. In addition, barium enema may sometimes mistake fecal masses or other benign lesions for tumors. Therefore, this method is recommended to be used instead of colonoscopy as a diagnostic examination only when there are no conditions for colonoscopy. According to statistics, the false positive rate of barium enema for colorectal cancer is about less than 1%, 5% to 10% for large polyps, and the misdiagnosis rate for small polyps can be as high as 50%. When performing barium enema, attention should be paid to using the air-barium contrast method to observe small mucosal lesions, as well as the morphology of the intestine after barium filling, especially the folded part of the intestine such as the sigmoid colon. Multiple postures should be adopted and repeated observations should be made to avoid missing lesions.

4. Electronic colonoscopy is considered the gold standard for colorectal cancer diagnosis because it allows direct visual observation, can take photos and videos, and can biopsy tissue specimens for pathological diagnosis. It can also perform surgical treatments such as removal of pedunculated lesions in different parts of the large intestine. Some people believe that the 33% reduction in colorectal cancer mortality achieved by fecal occult blood screening in Minnesota, USA, is due to the high false positive rate of fecal occult blood, which led to a large number of colonoscopy examinations, thus "opportunistically" discovering many early colorectal cancers and adenomas. It is speculated that at least 1/3 to 1/2 of the reduction in mortality in this group of survey subjects is the result of colonoscopy. A study has compared the sensitivity of colonoscopy and other colorectal cancer examination methods in various colorectal diseases and found that colonoscopy has the highest sensitivity. Colonoscopy can not only clarify the nature of questionable lesions in barium enema examination, but also discover many small adenomas and cancers that were missed by barium enema. Shinya found 43% of the 425 cases of colorectal cancer found by fiber colonoscopy during barium enema examination. Reilly reported that 92 patients with colorectal cancer underwent fiber colonoscopy after barium enema examination, and found that 7 cases (7.6%) were another primary cancer that was missed by barium enema. Currently, colonoscopy has shown indisputable superiority in the diagnosis of colorectal tumors and the removal and treatment of adenomas. Among the patients with colorectal cancer and adenoma admitted to the Affiliated Cancer Hospital of Fudan University School of Medicine in the past 10 years, more than 90% of their diagnoses were confirmed by colonoscopy.

After introducing barium enema and colonoscopy, we must also solemnly remind clinicians to pay attention: the above examinations must be performed with caution in patients who have clinical obstruction symptoms. This is because the use of laxatives to prepare the intestines before the examination can induce acute complete intestinal obstruction. Barium enema examinations in such patients may not only cause intestinal obstruction, but may also cause perforation of the colon distal to the lesion. Therefore, patients with more obvious obstruction symptoms should be contraindicated for the above two types of examinations.

5. CT and simulated colonoscopy techniques are generally superior to CT in observing the morphological changes in the colorectal cavity. However, CT helps to understand the extent of cancer invasion, and its greatest advantage is that it can show the involvement of adjacent tissues and organs, and whether there is metastasis to lymph nodes or distant organs. Early colorectal cancer lacks specific signs on ordinary CT examinations. Occasionally, there may be localized thickening of the intestinal wall, but it is difficult to distinguish the nature of the lesion. In the middle and late stages of cancer, eccentric lobed masses, annular or semi-annular thickening of the intestinal wall, intestinal stenosis, and widespread stiffness of the intestinal wall can be seen in the intestinal cavity. When the tumor penetrates the intestinal wall, the intestinal wall appears blurred. In recent years, due to the development of CT hardware facilities and computer technology, radiologists use spiral CT to perform cross-sectional scans at different levels along the axis of the large intestine after inflating the intestinal tube, and then use computers to perform three-dimensional reconstruction to draw simulated colon images. This technology is called virtual colonoscopy. The disadvantage is that if the intestine is not cleaned thoroughly, feces may be mistaken for a tumor. If the colon is not well inflated, the intestinal cavity cannot expand and it may be misjudged as intestinal stenosis. When the intestine is over-inflated, gas enters the small intestine and affects the scanning results of the large intestine. In addition, this method cannot show changes in mucosal color and texture like traditional colonoscopy, and it is difficult to find flat lesions. However, with the continuous advancement of technology, it may be possible to gradually solve the above defects in the future. If suspicious lesions are found during the examination, traditional colonoscopy and biopsy should still be performed.

6. For patients whose diagnosis of intestinal tumors is still unclear, MRI can make up for the shortcomings of CT diagnosis. MRI is easy to understand the infiltration of perirectal fat, so it is helpful to find or identify stage III patients.

7. Type B Ultrasound Examination Type B ultrasound examination includes two methods: through the abdominal wall and intestinal cavity examination:

(1) Examination through the abdominal wall: ① Directly examine the location, size, and relationship of the primary intestinal tumor with surrounding tissues; ② Examine metastatic lesions, including the retroperitoneal and mesenteric root lymph nodes, abdominal and pelvic cavities for metastatic nodules or masses, and the presence of space-occupying solid masses in the liver.

(2) Transintestinal examination: A special fiber-optic ultrasound endoscope is used to fill water between the ultrasound sensor and the intestinal wall. A special water bag is wrapped around the ultrasound sensor, or a balloon is wrapped around the sensor and then injected with water to allow the sensor to be measured through water. The measured image shows five layers of the intestinal wall, namely, the mucosal layer, the muscularis mucosa, the submucosal layer, the muscularis propria, and the serosa. The shape, thickness, and uniformity of each layer are observed to indicate the range and size of the tumor, whether it has infiltrated outside the intestinal cavity, etc., and even the corresponding conditions of adjacent organs such as the prostate, bladder, uterus, and vagina can be detected.

It is generally believed that due to the large amount of gas in the intestinal cavity, it is difficult to distinguish intestinal wall lesions through transabdominal ultrasound, especially for early colorectal cancer, but the detection rate for mid- and late-stage colorectal cancer can still reach more than 90%. The accuracy of intracavitary B-ultrasound examination in staging cancer is significantly higher than that of transabdominal ultrasound examination. It has been reported that the accuracy of intracavitary B-ultrasound in estimating the infiltration range can reach 76% to 88.8%, but the accuracy of extraintestinal lymph node metastasis is only 38%.

The above is some knowledge about colorectal cancer that we have prepared for you today. I hope it will be helpful to you. If you have any other needs, you can also consult our online consulting experts of Feihua Health Network. We are always here to answer your questions. Feihua Health Network is always by your side and cares about your health issues! Feihua Health Network wishes you good health!

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