| Colon carcinoma is the most common malignant tumor in human, postoperative metastasis and recurrence are responsible for a large proportion of treatment failures. About 30%-40% of patients will experience the development of metastasis or recurrence after radical resection of the primary lesion in 5 years, but the metastasis have not been dectected by conventional examinations(operation ,B type ultrasound ,CT ,histological section) in preoperation and postoperation., therefore the small metastasis foci exits objectively. We call this micrometastasis which is small, diffecuilt to be discovered in routine examinations and exists in the blood circulation, lymph node, marrow and other tissues or organs. Micrometastasis is a vague,undefined concept that is applicable to all malignant tumor and changes with the development of technology. Micrometastasis has been advocated by many investigator, usually it isa metastases foci consisted by one to a few cancer cells disseminatingthrough blood and lymph and no more than 2mm. Examinating occultmetastases cells may benefit from judgement of prognostication. The others think the so-called micrometastasis is the tumer metastases in the casinomer by conventional histological examination, it has different sense in many issue.It is possible to form fatal dominat metastasis lesion, so it is positive significant for definiting treatment plan and judging prognosis to identifying the existence of micrometastasis. There are some methods to detect micrometastasis such as continuous pathological section, immunohistochemistery, radio-immunity, flow cytometry, molecular biology technique. These methods have either advangtages and disadvangtages respectively. Immunology technique and molecular biology technique have embodied their superiority and clinical value, it can be selected according to different conditions. With the development of technique, it is sure that molecular biological technique will be applied to the clinical field even further, and RT-PCR would become the routine method to check colon cancer in the future. RT-PCR technique is very highly sensitive, this methods has been finished by amplifications of aim gene. CK-19 gene is expressed exclusively in tumor tissues and normal epithelial tissue which the tumor originates, but not in normal lymphocytes and marrow. Positive result should be achieved if only it exists a very small quantity of target RNA of tumor tissues. The RT-PCR method is sensitive enough to detect a tumor cell among 105-107normal cell (lymphocytes, peripheral blood cells, marrow cells etc.). CK-19mRNA detectability in normal/nontumorous peripheral blood, bone marrow or lymph node varied from 0-20%. This may depend on the selection of control subjects, techniques and ewperimental design. In this study, RT-PCR method has been used to detect the expression of cytokeratin-19 in peripheral blood lymphocytes because CK19 expresses only in tumour tissues, not in normal lymph nodes.Detection of CK19 mRNA in peripheral blood lymphocytes and cancer cells by RT-PCR can be considered as a new early-diagnosic method. In this study, we collected lymphocytes in peripheral blood and tumor tissues from 41 patients with colorectal cancer and 8 patients with innocent intestinal diseases and 8 healthy persons as negative controls, Special care was taken to prevented contamination by tumor cells and normal epithelial cells. After separated from, it is immidietely preserved in deep freeze equipment in -80℃. until subsequent RNA extraction. After extracting RNA, Reverse transcription PCR (RT-PCR) was then carried out to detect the expression of CK-19. All of these tumor tissue samples were CK19 positive by RT-PCR, with a 460bp strap. There was a negative result in innocent diseases and healthy persons. The positive rate of colorectal cancer patients was 41.5% (17/41) for single sampling and 65.9% (27/41) for repeated sampling. The positive rate of Dukes A, B, C and D stage is 28.6% (2/7),58.8% (10/17),83.3% (10/12) and 100% (5/5) respectively. Special attention shoud be paid to the avoidance of false postiveresult because RT-PCR is a sensitive method. A main cause for the occurrence of false-postive result is contamination of carry-overproducts from the previous PCR amplifications. Another cause iscontamination of peripheral blood by normal epithelial cell. The K19 RT-PCR method is unlikely to be flawed by a...
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