Tissue hemoglobin oxygen saturation (i.e. oxygenation) is a functional imaging endpoint that can reveal variations in tissue hypoxia which may be predictive of pathological response in subjects undergoing Neoadjuvant Chemotherapy (NCT). In this study we used Diffuse Optical Spectroscopic Imaging (DOSI) to measure concentrations of oxyhemoglobin (ctO2Hb), deoxy-hemoglobin (ctHHb), total Hb (ctTHb = ctO2Hb + ctHHb) and oxygen saturation (stO2=ctO2Hb/ctTHb) in tumor and contralateral normal tissue from forty-one patients with locally advanced primary breast cancer. Measurements were acquired prior to the start of neoadjuvant chemotherapy. Optically derived parameters were analyzed separately and in combination with clinical biomarkers to evaluate correlations with pathologic response. Discriminant analysis was performed to determine the ability of optical and clinical biomarkers to classify subjects into response groups. Twelve (28.6%) of 42 tumors achieved pCR and 30 (71.4%) were non-pCR. Tumor measurements in pCR subjects had higher stO2 levels (median 77.8%) than those in non-pCR individuals (median 72.3%, p = 0.01). There were no significant differences in baseline ctO2Hb, ctHHb, and ctTHb between response groups. An optimal tumor oxygenation threshold of stO2 = 76.7% was determined for pCR vs. non-pCR (sensitivity = 75.0%, specificity = 73.3%). Multivariate discriminant analysis combining estrogen receptor (ER) staining and stO2 further improved the classification of pCR vs. non-pCR (sensitivity = 100% specificity = 85.7%). These results demonstrate that elevated baseline tumor stO2 are correlated with a pathologic complete response. Non-invasive DOSI scans combined with histopathology subtyping may aid in stratification of individual breast cancer patients prior to NCT.

Abstract. Near-infrared (NIR) (650 to 1000 nm) optical properties of turbid media can be quantified accurately and noninvasively using methods based on diffuse reflectance or transmittance, such as frequency-domain photon migration (FDPM). Conventional FDPM techniques based on white-light steady-state (SS) spectral measurements in conjunction with the acquisition of frequency-domain (FD) data at selected wavelengths using laser diodes are used to measure broadband NIR scattering-corrected absorption spectra of turbid media. These techniques are limited by the number of wavelength points used to obtain FD data and by the sweeping technique used to collect FD data over a relatively large range. We have developed a method that introduces several improvements in the acquisition of optical parameters, based on the digital parallel acquisition of a comb of frequencies and on the use of a white laser as a single light source for both FD and SS measurements. The source, due to the high brightness, allows a higher penetration depth with an extremely low power on the sample. The parallel acquisition decreases the time required by standard serial systems that scan through a range of modulation frequencies. Furthermore, alldigital acquisition removes analog noise, avoids the analog mixer, and does not create radiofrequency interference or emission.