Evaluation of HER2 status is critical in determining appropriate treatment for 
breast cancer. Currently, Fluorescence In Situ Hybridization (FISH) and 
Immunohistochemistry (IHC) are the FDA-approved tests. Studies show, FISH is 
superior to IHC in accuracy and prediction of clinical outcomes with respect to 
response to anti-human epidermal growth factor receptor 2 (HER2) therapy 
trastuzumab. The impact of factors on choice of test for HER2 detection was 
determined using logistic regression. We show that geographic location, cancer 
stage, and diagnosis date have significant effects on choice of test. These 
findings indicate that disparities may be present in breast cancer care, and 
highlight the importance of testing guidelines.