Tissue concentration of systemically administered antineoplastic agents in human brain tumors

The blood-brain-barrier (BBB) limits the penetration of many systemic antineoplastic therapies. Consequently, many agents may be used in clinical studies and clinical practice though they may not achieve therapeutic levels within the tumor. We sought to compile the currently available human data on antineoplastic drug concentrations in brain and tumor tissue according to BBB status. A review of the literature was conducted for human studies providing concentrations of antineoplastic agents in blood and metastatic brain tumors or high-grade gliomas. Studies were considered optimal if they reported simultaneous tissue and blood concentration, multiple sampling times and locations, MRI localization, BBB status at sampling site, tumor histology, and individual subject data. Twenty-Four studies of 19 compounds were included. These examined 18 agents in contrast-enhancing regions of high-grade gliomas, with optimal data for 2. For metastatic brain tumors, adequate data was found for 9 agents. Considerable heterogeneity was found in the measurement value, tumor type, measurement timing, and sampling location within and among studies, limiting the applicability of the results. Tissue to blood ratios ranged from 0.054 for carboplatin to 34 for mitoxantrone in high-grade gliomas, and were lowest for temozolomide (0.118) and etoposide (0.116), and highest for mitoxantrone (32.02) in metastatic tumors. The available data examining the concentration of antineoplastic agents in brain and tumor tissue is sparse and limited by considerable heterogeneity. More studies with careful quantification of antineoplastic agents in brain and tumor tissue is required for the rational development of therapeutic regimens.