Abstract In breast cancers, one of the most troublesome characteristics for cure is the heterogeneity in point of genetic alterations, treatment-response variability, and histopathological features. This characteristic urgently requires personalized tailored therapy, getting out of a simple and widespread prescription. Therefore, the investigation of multiple biomarkers is inevitable for complete recovery. Immunohistochemistry (IHC) has been a major diagnostic method in various malignancies and many studies showing the relationship between immunohistochemical profiles and molecular classification support that IHC might play a significant role in subclassification of breast cancer patients for personalized medicine. However, conventional IHC method is not adequate for examination of multiple biomarkers since it requires consumption of many tissue slices and proportionally increases diagnostic cost which can give a big burden to patients. In addition, subjective decision for biomarker expression is another major problem. Therefore, an innovative multiplexed IHC platform satisfying not only investigation of multiple biomarkers with reducing consumption of tissue slice but also quantification for the biomarkers is the current demand for personalized medicine. Here, a novel microfluidic multiplexed and quantitative IHC platform was developed for proteomic profiling of breast tumors. The large-scale microfluidic device was designed to have 20 microchannels, and multilayer soft lithography and two-step lithography technologies were used for fabrication. Fluidic resistance was considered for equivalent flow rate of individual reaction channel. Ten biomarkers known as predictive and prognostic indicators in breast cancers, including SMM-HC, CK5, CK14, E-Cadherin, p53, ER, p63, PR, HER2, and Ki-67, were examined on four breast cancer cell lines (MCF-7, SK-BR-3, AU-565, and HCC70) to confirm the massive multiplexed IHC. Results showed that the platform successfully realized the expressions of each biomarker on a cellblock at the same time and proteomic profiling for 10 biomarkers could be quantitatively analyzed from the image analysis. The platform was also applied to a breast cancer tissue sample and the result was corresponded to the results of conventional IHC method. This microfluidic platform is expected to realize precise subtyping of cancer patients by the proteomic profiling even though the size of tumor samples acquired by operation has been getting smaller due to early detection and neoadjuvant therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3992.