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The study of microsatellite instability (MSI) has provided the evidence to support asequential, progressive pathway for the development of cancer. In this study, we analyzed the role of MSI at chromosome 11p15.5 using microdissection of paraffin-embedded tissue from 68 matched normal and breast tumor samples. Components of intraductal, invasive and metastatic foci in lymph node were assessed for MSI using the polymorphic markers D11S922, tyrosine hydroxylase (TH) and D11S988. We found that MSI at D11S922 was relatively high incidence than other two markers and increased during breast cancer progression. The overall frequency of MSI at D11S922 was 26.7% in pure intraductal carcinoma, 36.4% in invasive carcinoma, and 40.0% in invasive carcinoma with metastases. We observed no significant correlation between MSI at chromosome 11p15.5 and the patient`s age, tumor size, histological grade, or lymph node metastasis. We compared the MSI incidence with the expression of prognostic markers, such as p53, c-erb B2, estrogen receptor, and progesterone receptor, and found no significant correlation. We suggest that the MSI of chromosome 11p15.5 is increased during breast cancer progression, but long-term follow-up study would establish whether MSI at chromosome 11p15.5 could be useful as a potential prognostic marker for breast cancer
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