Intrinsic tumor biomarkers revealed by novel double-differential spectroscopic analysis of near-infrared spectra.

We develop a double-differential spectroscopic analysis method for broadband near-infrared (NIR, 650 to 1000 nm) absorption spectra. Application of this method to spectra of tumor-containing breast tissue reveals specific cancer biomarkers. In this method, patient-specific variations in molecular composition are removed by using the normal tissue as an internal control. The effects of concentration differences of the four major tissue absorbers (oxyhemoglobin, deoxyhemoglobin, water, and bulk lipid) between the tumor and normal tissue are accounted for to reveal small spectral components unique to cancer. From a pilot study of 15 cancer patients, we find these spectral components to be characterized by specific NIR absorption bands. Based on the spectral regions of absorption at about 760, 930, and 980 nm, we identify these biomarkers with changes in state or addition of lipid and/or water. To quantify spectral variation in the absorption bands, we construct the specific tumor component (STC) index. The STC index identifies regions of the breast with tumors.