الفهرس 
BREAST CANCER
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Abstract
Breast cancer is the second most common cancer diagnosed worldwide. Human epidermal growth factor receptor 2 (HER2) positive breast cancer represents about 20-30 percent of all breast cancers. Trastuzumab is used in the treatment of HER2 positive breast cancer. Micro-RNA 21 (miR-21) is an oncomiR that acts by inhibiting many tumor-suppressor genes. We analyzed the relative expression levels of serum miR-21 in twenty HER2 positive metastatic breast cancer patients before and after three months treatment with trastuzumab. MiR-21 levels decreased with a high significant difference after trastuzumab therapy (p=0.001). Although miR-21 expression levels were lower in responders than in non-responders, the difference was not statistically significant (p=0.6). Our results demonstrated significant negative correlation between its basal expression, expression levels after treatment and time to progression (TTP) (p=0.03, p=0.01 respectively). These results make miR-21 a potential prognostic factor for HER2 positive metastatic breast cancer patients. Additionally, it can be an attractive target for those patients. Antisense oligonucleotides for miR-21 might be potential therapeutic agents.