The Assessment of Using Microsatellite Alterations in the Plasma DNA as Biomarkers for the Early Detection of Micrometastasis and Occurrence of Non-small Cell Lung Cancer

• Main Authors: Hsu, I-Ting, 徐意婷
• Other Authors: Chien, Yi-Chih
• Format: Others
• Language: en_US
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/39580940369061057025

碩士 === 國立彰化師範大學 === 生物學系 === 93 === Lung cancers have been identified to cause one of the major lethality in the world. Non-small cell lung cancer (NSCLC) is one of the two major types of lung cancers. Patients with NSCLC always have very poor prognosis mainly due to late diagnosis, and high rates of micrometastasis, which is the metastatic tumors cannot be detected with current methods in clinic. Current clinical methods of detecting metastasis are not sensitive enough, therefore it’s urgent to develop a more specific and sensitive method. The developing method is to search for microsatellite alterations in plasma DNA in order to use them as biomarkers for detecting micro-metastasis. Scientists have found that the plasma DNA of cancer patients has neoplastic characteristics, such as LOH and MSI. Microsatellite DNA could be detected fast and easily by PCR, which makes it be a good biomarker to detect LOH or MSI in the plasma DNA. According to the ratio of heterozygosity, microsatellite alterations (MA) in tumor and plasma DNA, microsatellite markers were classified into four grades. Markers with heterozygosity?70%, MA in tumor DNA?50%, and MA in both tumor and plasma DNA?30% were classified as the grade I markers; those with heterozygosity?70%, MA in tumor DNA?50%, and MA in both tumor and plasma DNA<30% were classified as the grade II markers; those with heterozygosity?70% and 25%?MA in tumor DNA<50% were classified as the grade III markers; while those with heterozygosity?70% and MA in tumor DNA<25% were classified as the grade IV, which was considered as unsuitable markers. The grade I markers were regarded as the idealist markers for detection of micro-metastasis. Besides, the markers for the early detection of tumor occurrence could be found by their MA% in the normal tissue DNA. Therefore the aims of this research were to search for grade I microsatellite markers and those had altered in the early stage of the development of NSCLC. 26 NSCLCs were screened with 17 microsatellite markers distributed on 15 chromosome arms. We found that grade I markers were D3S1300, D8S277 and TP53, and the marker altered at the earliest stage of the development of NSCLC was D18S61. These four markers were then tested in control groups, including 46 non-tumor individuals, 30 non-NSCLC patients, to see their specificity to NSCLCs. MA% in the plasma DNA at D8S277 and D18S61 had no significant difference between NSCLC patients and two control groups. And TP53 had no significant difference in MA% in the plasma DNA between patients with NSCLC and non-NSCLC patients. Therefore, D8S277 was further selected out from grade I markers, and D18S61 was considered unsuitable for early detection. Besides, we found MA at D3S1300 associated with older age and smoking, and TP53 related to poor differentiation. FRL index was the highest in the tumor DNA, indicating tumor cells have the highest extent of allelic loss. In conclusion, D3S1300 was thought to be the most proper and specific marker for NSCLC. However, TP53 was considered as a universal marker for detecting cancers. We suggested TP53 should be examined first to screen if having cancers or not, and then D3S1300 is tested to see if cancers are NSCLCs when practicing in clinic.