HER2 breast cancer is an aggressive disease that occurs in 20 - 30% of the breast cancer population. Treatment for HER2 breast cancer includes use of an anti-HER2 monoclonal antibody, trastuzumab. Testing for HER2 is of critical importance due to the adverse side effects and substantial costs associated with this anti-HER2 treatment. Currently, two kinds of tests, Fluorescence In Situ Hybridization (FISH) and Immunohistochemistry (IHC), are FDA approved for determination of HER2 status in breast cancers. Clinical and non clinical factors that affect the choice HER2 test and the use of anti-HER2 therapy in breast cancer were analyzed using a data set containing information from six outpatient oncology clinics in the United States. The analysis showed that geographic location, cancer stage, and diagnosis date (pre- or post-publication of testing guidelines) have significant effects on choice of test. With regard to trastuzumab prescription, geographic location and HER2 status have significant effects on the prescription of trastuzumab. In addition, there was a non-significant trend for certain Medicare patients not to receive trastuzumab therapy. These findings indicate that disparities are present in breast cancer care based on geography and cancer stage, and highlight the importance of testing guidelines. The cost effectiveness of FISH vs. IHC was determined, by considering the financial and health-related costs associated with testing and subsequent treatment as well as the accuracy of each test. The results show that FISH is the optimal choice for HER2 testing and is more cost-effective than IHC.

Indiana University-Purdue University Indianapolis (IUPUI) / Cancer stem cells (CSCs) are proposed to play a major role in tumor progression, metastasis, and recurrence. The Human Epidermal growth factor Receptor 2 (HER2) gene is amplified and/or its protein product overexpressed in approximately 20% of breast cancers. HER2 overexpression is associated with increased CSCs, which may explain the aggressive phenotype and increased likelihood of recurrence for HER2+ breast cancers. Telomerase is reactivated in tumor cells, including CSCs, but has limited activity in normal tissues, providing support for the use of telomerase inhibition in anti-cancer therapy. Telomerase inhibition via an antagonistic oligonucleotide, imetelstat (GRN163L), has been shown to be effective in limiting cell growth in vitro and limiting tumor growth. Moreover, we have previously shown imetelstat can decrease metastases to the lungs, leading us to question if this is due to imetelstat targeting the CSC population. In this thesis, we investigated the effects of imetelstat on CSC and non-CSC populations of HER2+ breast cancer cell lines, as well as a triple negative breast cancer cell line, which lacks HER2 overexpression. Imetelstat inhibited telomerase activity in both CSC and non-CSC subpopulations. Moreover, imetelstat treatment alone and in combination with trastuzumab significantly reduced the CSC fraction and inhibited CSC functional ability, as shown by a significant decrease in mammosphere counts and invasive potential. Tumor growth rate was slower in combination treated mice compared to either drug alone. Additionally, there was a trend toward decreased CSC marker expression in imetelstat treated xenograft cells compared to vehicle control. The decrease in CSC marker expression we observed occurred prior to and after telomere shortening, suggesting imetelstat acts on the CSC subpopulation in telomere length dependent and independent mechanisms. Our study suggests addition of imetelstat to trastuzumab may enhance the effects of HER2 inhibition therapy.