1.Fecal occult blood test (FOBT) is one of the main tools for early detection of colon cancer. 1967 Greegor first used FOBT as a screening test for colon cancer in asymptomatic people, and it is still a practical screening tool today. Chemical methods include benzidine test and guaiacol test, but their specificity is not satisfactory. Immunological methods include single amplification immunoassay (SRID), latex agglutination (LA), convective immunoelectrophoresis (CIE), immunoenzymatic assay (ELISA) and reverse indirect hemagglutination (RPHA), among which RPHA is more suitable for mass screening. 63.6% sensitivity of RPHA is lower than 72.7% of benzidine, while 81.9% specificity of RPHA is higher than 61.7% of benzidine. The specificity of RPHA is 81.9%, which is higher than that of benzidine (61.7%). Therefore, RPHA as primary screening can significantly reduce the amount of re-screening population, and it is not necessary to control the diet, so it is easily accepted by the screening population.
The immunospot method (dot-ELISA) reported in recent years is a new immunological technique for future development, which is relatively easy to operate, with high sensitivity and good reproducibility, and has a real prospect of clinical application.
2.Cytological diagnosis Colon cancer exfoliative cytological examination methods include: rectal irrigation, brush under direct vision of colonoscopy, wire mesh balloon erasure and finger smear method at the lesion. However, it is more practical to take the brush under colonoscopy or finger-examination smear at the focal area, and it has diagnostic significance if malignant cells are found. If the cells are suspicious of malignancy or nuclear heterogeneous cells with slightly larger nuclei and increased chromatin, it is not enough for final diagnosis, but it is suggested that review or biopsy should be performed to confirm the diagnosis. Although the exfoliated cells find malignant tumor cells, the histopathological diagnosis should still be used to determine the treatment plan.
Histopathological examination of biopsy specimens is a necessary basis for treatment planning. The main points of biopsy specimens are
(1) Polyp-like mass: If the tumor is small, all the mass should be cut and sent for examination, and the tip should be included, if there is no obvious tumor tip, the basal mucosa of the mass should be cut and sent for examination at the same time.
(2) When biopsy is performed on larger masses, care should be taken to avoid clamping necrotic tissues on the surface of the masses, and if possible, the tissues at the junction of the tumor base and normal mucosa should be clamped as much as possible. If necessary, especially when adenoma is suspected to be cancerous, it is advisable to take material from multiple locations.
(3) The ulcerated lesions should be taken from the margins of the ulcer, and the degenerated and necrotic tissues of the ulcerated surface should not be taken.
For small pieces of biopsies, during the production process, attention should be paid to the direction of mucosal embedding as much as possible to ensure that the longitudinal section of the glandular duct can be observed in the section.
4.Serum carcinoembryonic antigen (CEA) determination Initially, Gold extracted r-cell membrane glycoprotein from human colon and pancreatic cancer tissues in 1965, and found that it also exists in endoderm-derived gastrointestinal adenocarcinoma and liver, intestinal and pancreatic tissues of 2-6 month old embryos, so it was named CEA, and it was thought that it belongs to the specific determination of colon cancer, which was also confirmed by subsequent work. The CEA content in colorectal cancer tissues is clearly higher than that in normal tissues, which shows that it is used as a basis for diagnosis, but after increasingly widespread use and further analysis, it is found that CEA is also present in stomach (49%-60%), lung (52%-77%), breast (30%-50%), pancreatic (64%), thyroid (60%) and bladder tumors. Therefore, CEA is a malignant tumor-associated antigen, with the largest proportion of positivity in colon cancer and a higher rate in liver metastases. It has been reported that in 20 cases of colorectal cancer, CEA levels in portal vein and peripheral vein were significantly higher than those in peripheral blood, indicating that the liver has a role in removing CEA, but the mechanism is still unclear. In recent years, CEA measurement has been widely used in clinical practice, and its clinical significance is summarized as 2 aspects.
The prognosis can be predicted by preoperative CEA, and those with elevated CEA have a high recurrence rate and a worse prognosis than those with normal CEA values. The normal value criteria of CEA, according to the sensitivity and specificity of different criteria and the correct index obtained from its predictive value, the highest correct index (0.43) is >5 μg/L, which is more appropriate than other levels (Table 3). Therefore, it would be more appropriate to use the enzymatic method ≤5μg/L as the standard of normal value.
②Postoperative follow-up to predict recurrence or metastasis: for those with increased CEA before surgery, the radical surgery should be normalized within 6 weeks or 1-4 months, and those who remain high may have residual, and it is believed that the CEA is already elevated 10 weeks to 13 months before the performance of recurrence symptoms, so those with increased CEA values after radical surgery should be closely examined and followed up, and if necessary, a second surgical exploration is advocated. CEA is more sensitive in liver and retroperitoneal metastases, but less sensitive in lymph node and lung metastases. The authors counted 115 cases with elevated CEA who underwent dissection and 47 recurrences (40.1%). Martin reported that 93.3% of the 60 cases who underwent reoperation based on elevated CEA had confirmed recurrence, 95% of those with liver metastases had elevated CEA, and 17%-25% of those with metastases or recurrence generally had normal CEA levels. CEA-led second dissection is the best method to improve the survival rate of recurrent colorectal cancer.
With the research of molecular genetics of tumor, the development and application of in vitro gene amplification technology polymerase chain reaction (PCR) has provided the possibility of tumor genetic diagnosis. . It has been studied and applied in colon cancer in the following 2 areas.
(1) Determining the mutation rate of Ki-ras gene in colorectal cancer and paraneoplastic tissues: it helps to understand the malignancy of the tumor and provide a prognosis for its participation. ras gene exists in many human tumors and is a potential tumor marker. Single point mutation can turn ras gene into oncogene. In 35 cases of colorectal cancer in China, Dryer et al. detected 11 cases (31.4%) with codon 12 mutation, 1 case (2.9%) with codon 61 mutation, and 1 case with codon 12 mutation in paracancerous tissue only, while the more common codon 13 Gly→AsD mutation in this paper was not found in colon cancer (Table 4). This method can be further researched and applied to help identify small tissues as cancerous or not.
(2) Detection of mutated Ki-ras gene in stool: Dryer et al. isolated macromolecular DNA from stool for PCR amplification of exon 1 of Ki-ras gene, and detected the mutation of codon 12 of this gene by RFLP method, and found 6 cases with Ki-ras gene mutation among 18 colorectal cancer patients (33.3%), among which 4 cases were also found to have corresponding mutation in cancer tissue. Volgelstein et al. examined the stool of 24 cases of suspected colon cancer, 9 cases had ras gene and 8 cases had mutation, this test can be used to monitor people with high suspicion but not detected by general methods, and has practical application for early detection of colorectal cancer.
6.Fiber colonoscopy The application of fiber colonoscopy is an important progress in the diagnosis of colon tumor, which also improves the early diagnosis rate. The application of short fiber sigmoidoscopy gradually replaces 30cm hard sigmoidoscopy, and from the effect of 2 types of scopes, the detection rate of cancer lesions is 2 times higher in fiberscopy than in hardoscopy, and the detection rate of adenoma is 6 times higher. Since fiberoptic sigmoidoscopy is easy to grasp and apply, it has been widely used to screen high-risk groups. Endoscopy, in addition to naked eye observation and biopsy for pathological diagnosis, can also remove lesions with tissues in different parts for surgical treatment. For those who are difficult to identify on X-ray, microscopy can be used to further confirm the diagnosis. In addition to confirming symptomatic patients, it can also be used to screen asymptomatic people in high-risk groups.
7.Imaging diagnosis The purpose of imaging examination is to detect infiltration and metastasis, and the estimation of the depth of infiltration is very important. The rate of lymph node metastasis is 6%-11% if the tumor is limited to submucosa, 10%-20% if beyond submucosa, and 33%-50% if full infiltration.
(1) Colon gas-barium double imaging: It is an important examination method for colon lesions, but it is not suitable for population screening. Double gas-barium contrast imaging is significantly better than single barium contrast examination, the former detection rate is up to 96%, similar to colonoscopy; The detection rates for polyps were 87% and 59%, respectively. In experienced patients, the detection rate of double imaging can reach 96%, which is close to the result of colonoscopy, but X-ray imaging also has shortcomings, which can cause false negatives due to fecal or sigmoid disc rotation, and the false negative rate can reach 8.4%.
Examination points.
①Intestinal preparation is contraindicated with clean bowel washings, with a crumbless diet plus oral laxatives, and only after excretion of feces.
(②Before instilling 70% to 80% barium sulfate with drug (654-2) static injection, so that the colon is hypotonic, fluoroscopic instillation of barium until the hepatic flexure can be shown, followed by the injection of gas up to the sense of abdominal distension.
③The subject changes position, taking supine and left and right oblique position, standing position and supine position, right anterior oblique position, etc. to fully display the left half, right half, cecum and other parts. We should pay attention to the presence of filling defects, intestinal wall stiffness and stenosis, and niche shadowing, and especially to the presence of malignant signs in the diagnosis, such as stiffness, ulceration, and basal bowel wall wrinkling at the head of polyps (Figure 4); in the presence of cancer, we should observe the presence of small polyps in other parts of the colon; in those under 40 years old with multiple polyps, we should consider the possibility of familial adenomatosis.
(2) CT scan: For the observation of morphological changes in the lumen of the colon, air-barium enema is generally better than CT, but CT can help to understand the degree of cancer invasion, and CT can observe the limited thickening and protrusion of the intestinal wall, but sometimes it is difficult to distinguish benign from malignant at an earlier stage. proposed the following CT staging method.
Stage 1: normal thickness of the GI canal wall (usually 5 mm) with polyp-like lesions protruding into the lumen.
Stage 2: Localized thickening of the canal wall with uniform plaque or nodular manifestations without extra-mural extension.
Stage 3: localized thickening of the duct wall with direct invasion of surrounding tissues; there may be limited or regional lymph node involvement without distant metastasis.
Stage 4: distant metastasis (e.g. liver, lung, distant lymph nodes).
CT examination has been used as one of the routine examination methods because it helps to understand the extent of tumor, helps to preoperative staging, estimate the extent and formulate treatment plan, and is also one of the indicators to estimate the prognosis. However, some materials suggest that the correct rate of CT preoperative staging is 48%-72%, and the correct rate of estimating lymph node metastasis is 25%-73%, so it seems difficult to be used as a routine examination for staging, but the detection rate of liver or metastatic nodes is more meaningful.
(3) MRI: If the diagnosis of intestinal tumor is still not clear, MRI can make up for the deficiency of CT diagnosis. MRI is easy to understand the infiltration in the fat around the rectum, so it can help to detect or identify stage 3 patients.
(4) Diagnosis by ultrasound section imaging: Ultrasound examination of colon tumor can be used for the following 2 aspects, namely, transabdominal wall or transintestinal lumen examination.
(1) Transabdominal wall examination: to directly examine the site, size and relationship with surrounding tissues of the primary intestinal mass; to examine metastatic foci: including retroperitoneal, mesenteric root lymph nodes, metastatic nodes or masses, the presence of metastatic nodes in the pelvis; and the presence of occupying substantial masses in the liver.
Trans-intestinal lumen examination: A special fiber ultrasound endoscope is applied, and the ultrasound transducer is filled with water between the ultrasound transducer and the intestinal wall, and a special water bladder is wrapped around the ultrasound transducer, or an air bladder is wrapped around it to enter the intestinal lumen and then water is injected, so that the transducer can be measured with water. The measured images showed 5 layers of the intestinal wall, namely, mucosal layer, mucosal muscle layer, submucosal layer, intrinsic muscle layer and plasma layer, and the muscle layer was hypoechoic, while the remaining 3 layers showed strong echogenicity. The correctness of the estimation of the infiltration range by various methods was compared in the following order: intracavitary ultrasound, endoscopy and CT scan.
(5) Nuclear diagnosis: The use of nuclear for the diagnosis of intestinal cancer includes.
(①Serological determination of tumor-related substances such as CEA, AFP, CA-50, CA19-9, etc.
②Nuclide diagnosis used as localization, from a specific nuclide material concentration status in the primary or metastatic tumor site, size, etc., commonly used are 67Ga-citrate, 2-5cm (74-165mEq, intravenous injection), 24-96h later, the focal site camera or tomographic image (ECT) with γ camera, there is radioactive accumulation in the cancer site, but in the bone, liver, large joints around the normal 131I is also commonly used to label CEA for injection into the body to detect the lesion site.