This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Purpose) Non-invasive optical methods may characterize tumors metabolically and may be a useful prognostic tool to guide treatment strategies. Diffuse Optical Spectroscopic Imaging (DOSI) is an emerging optical imaging technology that employs near-infrared light to quantitatively characterize tumor metabolic properties via hemodynamics. We evaluated the correlation between in vivo DOSI measurements of breast tumors and ex vivo clinical and immunohistochemical markers of tumor aggressiveness and proliferation. (Methods) A broadband DOSI instrument (650-1000 nm) was utilized to measure the concentrations of oxy-hemoglobin (ctO2Hb), deoxy-hemoglobin (ctHHb), bulk water (ctH2O) and lipids, as well as oxygen saturation (stO2), of tumors in sixty-one patients with primary breast cancer. Tissue specimens were analyzed using immunohistochemical staining for Ki67, p53 and Glut-1. DOSI parameters were compared to these biomarkers and other clinicopathological properties such as tumor grade and size. (Results) ctO2Hb and ctH2O were positively correlated with tumor grade, Ki67 index, p53, and Glut-1 expression. ctH2O, but not ctO2Hb, was correlated with tumor size. There was also a suggestive relationship between tumor size, grade, Ki67, p53, and Glut-1. (Conclusion) ctO2Hb and ctH2O were associated with biomarkers of tumor aggressiveness, proliferation and glucose metabolism. ctO2Hb correlated with these biomarkers independent of tumor size. ctO2Hb measured using DOSI represents a potential non-invasive surrogate marker for aggressiveness, proliferation and glucose metabolism in breast cancer