Optical spectroscopic sensing of tumor hypoxia.

Tumor hypoxia is a critical indicator of poor clinical outcome in patients with cancers of the breast, cervix, and oral cavity. The ability to noninvasively and reliably monitor tumor oxygenation both prior to and during therapy can aid in identifying poor treatment response earlier than is currently possible and lead to effective changes in treatment regimen. Diffuse reflectance spectroscopy (DRS) has been used in several studies to measure tissue scattering, total hemoglobin content (THb), and vascular oxygenation (sO2) in tissue. In this study, we validate in vivo DRS-based measurements of vascular oxygenation using immunohistochemical staining of tumor hypoxia using pimonidazole, an established hypoxia marker. Using tumor xenografts grown from two different head and neck cell lines-UM-SCC-22B and UM-SCC-47-we demonstrate statistically significant negative correlations between tumor hypoxic fraction (HF) and THb (r  =    -  0.45; p  =  0.04) and sO2 (r  =    -  0.50; p  =  0.02). In addition, we also found a statistically significant positive correlation between HF and mean reduced scattering coefficient (r  =  0.60; p  =  0.005). Our results demonstrate that DRS-based measures of sO2 can provide reliable indirect measurements of tumor hypoxia that can be of significant utility in preclinical and clinical studies.