| Purpose: Colorectal cancer is one of the most malignant tumor. There is a gradual elevation tendency in morbidity. The malignant degree of colorectal cancer is higher. Although the patients can get some curative effect by operation, chemotherapy, radiotherapy and others multipurpose therapy, there are about 30-40% patients died of recurrence and distant metastasis. With the development of genes in colorectal cancer and molecular biology technique, it is possible to diagnose micrometastasis in lymph nodes, blood, marrow and other organs of colorectal cancer, which is hardly diagnosed by routine pathological method. The relationship between diagnoses of micometastasis and therapy and prognosis of patients is still in unceasing research and development. It is one of the focal points in clinical research about how to detect the micrometastasis in earlier stage. We confirm the existence of tumor cells applying RT-PCR to amplify the tumor marked target mRNA of patients' peripheral blood, which is a recent new technique to detect tumor cells in peripheral blood and marrow. The method make it possible detect the micrometastasis in peripheral blood and marrow on molecular level. As carcinoma cells are mostly derived from CK cells, we can confirm the origin of carcinoma cells by determinating CK. The foreign researchers regarded CK8, CK18, CK19 as marker of tumor metastasis, then they found the tissue specificity of CK20 was better than others. So in our study, we can accurately judge whether there is tumor micrometastasis in peripheral blood , peritoneal washes and lymph nodes or not applying RT-PCR to detect the tumor marked gene CK20 mRNA. It is very important significance to decide the tumor staging, multipurpose therapy and prognosis.Methods: 35 cases of colorectal carcinoma lymph nodes and peritoneal washes were collected from patients operated in the Surgery Department of the Fourth Hospital of Hebei Medical University during June 2002 to November 2002. Regional lymph nodes were collected within half an hour after the operation, fast frozen by the liquid nitrogen and reserve in –80℃ refrigerator. All specimens were verified by pathology. After the initial of the surgery, 200ml peritoneal washes were obtained, 100ml washes were done the peritoneal lavage cytology(PLC), RNA was extracted by Trizol method from the rest 100ml washes after centrifugation, after the gel electrophoresis and no degradation occurred, reverse transcribe was done. β-actin was the inner consultation standard by the transcribed cDNA, tumor cells existence were judged by CK20 expression through the amplification of the CK20 primers and the DNA band analysis of the amplified products by the gel scanner. According to the positive rate of CK20, we analyze and statisticed data by chi-square test. Results: 1. In the peritoneal washes of 35 lower rectal cancer patients, by PLC, 6 cases are positive, account for 17.1%, among them Dukes A 0, Dukes B 1(16.7%), Dukes C 4(19%), Dukes D 1(20%), the positive rate is increasing gradually. By RT-PCR, 25 cases are positive, account for 71.4%, among them Dukes A 1(33.3%), Dukes B 3(50%), Dukes C 16(71.2%), Dukes D 5(100%), positive rate is also increasing gradually by the improving of the Dukes A,B and C,D, there are significant difference in different stages, χ2=4.323, p＜0.05. By statistical analysis, the positive rate of RT-PCR examination is significantly better than the cytology examination, χ2=20.902, p＜0.05.2. In the specimens of circumference ＜1/2, by RT-PCR, 6 cases are positive about CK20 in peritoneal washes, account for 66.7%, while in that of circumference ≥1/2, 21 cases are positive, account for 80.8%. By statistical analysis, the positive rate of RT-PCR examination is no significant in different tumor circumference, χ2=0.754, p＞0.05. In addition, 10 tumors inside muscular layer, by RT-PCR, 4 cases are positive about CK20 in peritoneal washes, account for 40%. On the contrary, 25 tumors outside muscular layer, 21 cases are positive, account for 84%, it shows that the posi...
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