14023 Background: Response to neoadjuvant treatment is vital to predict a patient’s long-term survival. Precise detection of residual tumor cells after neoadjuvant chemotherapy would allow a better cosmetic results avoiding over surgery and reduce second operation due to positive margin status. Moreover, accurate prediction of pathological CR will yield no surgical intervention in certain population. Recently, a new generation of ultrasound platforms with real-time freehand elastography that enables the imaging of elasticity of the lesion by using the extended combined autocorrelation method (CAM) has become available. We are currently applying this technology to our patients with primary breast cancer in an attempt to assess response to neoadjuvant chemotherapy in comparison with MRI, conventional ultrasound and pathological findings. Methods: A total of 38 patients with primary breast cancer who underwent neoadjuvant chemotherapy and following surgical resection From May 2005 to Dec 2006 were included in this study. Board certified radiologists assessed the tumor response by MRI, US and US Elastography prior to surgery. Positive predictive value (PPV), and negative predictive value (NPV) for pathological CR (pCR) was assessed. Tsukuba Elastography score was applied for the assessment of Elastography. Results: 11/38 patients (28.9%) achieved a pCR in breast to neoadjuvant chemotherapy while no patients demonstrated progressive disease. The PPV for pCR of MRI and US was 54.5% and 36.3% respectively. The NPV of MRI and US was both 90.9%. None of the residual tumor mass with score 4 or 5 cases diagnosed by Elastography achieved pCR. When residual tumor image was detected by US, pCR was present in all 4 cases with score 1 or 2 Elatography. If the cut-off line is determined between score 3 and 4, the PPV and NPV for pCR by Elastography was 100% and 66.6% respectively. Conclusions: Elastography is easy to perform and it can provide an inexpensive, non-invasive, real-time tool for assessment of response to neoadjuvant chemotherapy among patients with primary breast cancer. In particular, Elastography might more effectively diagnose pathological CR. More patients are needed to evaluate the sensitivity and specificity of this new technology. No significant financial relationships to disclose.