δ-aminolevulinic acid-induced protoporphyrin IX concentration correlates with histopathologic markers of malignancy in human gliomas: The need for quantitative fluorescence-guided resection to identify regions of increasing malignancy

Abstract

Extent of resection is a major goal and prognostic factor in the treatment of gliomas. In this study we evaluate whether quantitative ex vivo tissue measurements of d-aminolevulinic acid-induced protoporphyrin IX (PpIX) identify regions of increasing malignancy in low- and high-grade gliomas beyond the capabilities of current fluorescence imaging in patients undergoing fluorescence- guided resection (FGR). Surgical specimens were collected from 133 biopsies in 23 patients and processed for ex vivo neuropathological analysis: P pIX fluorimetry to measure P pIX concentrations (CP pIX) and Ki-67 immunohistochemistry to assess tissue proliferation. Samples displaying visible levels of fluorescence showed significantly higher levels of CP pIX and tissue proliferation. CP pIX was strongly correlated with histopathological score (nonparametric) and tissue proliferation (parametric), such that increasing levels of CP pIX were identified with regions of increasing malignancy. Furthermore, a large percentage of tumor-positive biopsy sites (∼40%) that were not visibly fluorescent under the operating microscope had levels of CP pIX greater than 0.1 μg/mL, which indicates that significant P pIX accumulation exists below the detection threshold of current fluorescence imaging. Although P pIX fluorescence is recognized as a visual biomarker for neurosurgical resection guidance, these data show that it is quantitatively related at the microscopic level to increasing malignancy in both low- and high-grade gliomas. This work suggests a need for improved P pIX fluorescence detection technologies to achieve better sensitivity and quantification of P pIX in tissue during surgery. © 2011 The Author(s).