To adapt to the need of current public heath reform and education reform ,the aim of this study is to explore and improve practical teaching mode in preventative medicine for students in specialty of clinical medicine and set up normalized practical teaching base to enhance their concept of preventative medicine and enlarge their knowledge and increase their practical ability and social adoption.

As an emerging tumor marker, the rarity and heterogeneity of circulating tumor cells (CTCs) increase the difficulty of detection. In recent years, CTCs enrichment technology based on biophysical, biochemical and microfluidic properties has been continuously developed, which has promoted the research and application of CTCs in malignant tumors diagnosis, clinical treatment and prognosis evaluation. Although there are still some deficiencies in the detection of CTCs, with the interdisciplinary integration, CTCs will play increasingly important roles in the diagnosis and treatment of malignant tumors.

The incidence of gastric cancer ranks the fourth in all kinds of cancers in the world,ranking the second among patients with cancer-related deaths.The 5-year survival rate of gastric cancer patients is less than 30％.About 50％ of gastric cancer patients have recurred or metastasized after curative resection.Metastasis and recurrence are the major causes of death in cancer patients.CTCs play an important role in tumor metastasis.At present,there are more than 10 kinds of detection methods for CTCs in gastric cancer.The most widely used methods are RT-PCR,FCM,CelLTracks(R) AutoPrep(R) system and ISET.Recent studies have shown that CTCs in peripheral blood of patients with gastric cancer can be used to determine the clinical stage of patients,assess the prognosis and guide the individualized treatment of cancer.

There are many ways to identify circulating tumor cells in the current.Fluorescence has a wide range of applications in the identification of circulating tumor cells.The labeled cells can be observed and counted more intuitively by labeling the tumor cells with fluorescent group containing antibodies,probes and aptamers,and cytokine,CD45 and fluorescence in situ hybridization are widely used in the identification of various circulating tumor cell related tests.In recent years,people have explored the feasibility of using fluorescent probes to directly identify circulating tumor cells.With the development of biopsy probes and optical sectioning imaging technology of confocal microscopy,it is possible to directly identify circulating tumor cells with fluorescent probes in the future.