The longitudinal changes in these histopathologic end points were compared against changes in prominent optical parameters as shown in Figure 8, C and D. In the treated group, a major shift in both histology and optical end points was seen, whereas minimal changes were observed across all of these parameters in the control group. In this study, a combination of DRS and AFS was used to investigate cisplatin-induced changes in tumor physiology and morphology across a period of 1 week in a mouse model for

ALK activation hereditary breast cancer. The changes in optical end points were compared against the degree of pathologic response. The results showed that various DRS and AFS parameters in the treated animals significantly changed throughout the course of treatment relative to the untreated animals. These parameters were the Mie-scattering slope (P < .0001), Mie-to-total scattering fraction (P < .001),

tissue oxygenation (P = .035), fat volume fraction (P < .0001), and fluorescence residual (P < .018). Ipilimumab Furthermore, the observed changes appeared to be proportional to the degree of vital tumor tissue and the formation of fibrosis. Optical scattering characteristics are dependent on the size and density of cell nuclei and organelles as well as on the composition of the extracellular matrix (e.g., macromolecular aggregates and collagen fibers). In the histopathologic evaluation, considerable alterations in the extracellular matrix (formation of fibrosis) and in the size and the density of (sub) cellular structures were observed in the tumors of the treated animals. These morphologic and structural changes may lead to changes in tissue-scattering

properties that in turn may translate into changes in the Mie-scattering slope and Mie-to-total scattering fraction. Although significant fibrosis and cellular disintegration after treatment with cisplatin may explain these specific changes, further research is needed to provide a better understanding of these relationships. Tumor tissue oxygenation values of untreated animals remained hypoxic over time, whereas tumors of treated animals became progressively more oxygenated. This is consistent with Montelukast Sodium previously reported results where improved oxygenation of tumor tissue was observed due to tumor regression and altered metabolism after treatment with doxorubicin [27], [43] and [44]. For example, Vishwanath et al. performed DRS using a surface probe and showed that mammary-tumor tissue oxygenation in treated mice increased after doxorubicin administration relative to the untreated controls. A particularly interesting finding was the additional fluorescence observed in the treated group. On the basis of two-photon imaging, the extra fluorescence was specifically found in the cellular components of tumor tissue treated with cisplatin. Fluorescence was tumor specific and not observed in liver or muscle tissue of the treated animals.