There is a lack of understanding whether plasma levels of anticancer drugs (such as
pazopanib) correlate with intra-tumoral levels and whether the plasma compartment is the best surrogate for pharmacokinetic and pharmacodynamic evaluation. Therefore, we aimed to quantify
pazopanib concentrations in
tumor tissue, to assess the correlation between
tumor concentrations and plasma concentrations and between
tumor concentrations and efficacy. In this clinical trial, non-metastatic STS patients were treated with neo-adjuvant concurrent
radiotherapy and
pazopanib. Plasma samples and
tumor biopsies were collected, and
pazopanib concentrations were measured using liquid chromatography-tandem mass spectrometry. Twenty-four evaluable patients were included. The median
pazopanib tumor concentration was 19.2 µg/g (range 0.149-200 µg/g). A modest correlation was found between
tumor concentrations and plasma levels of
pazopanib (ρ = 0.41, p = 0.049). No correlation was found between
tumor concentrations and percentage of viable
tumor cells (p > 0.05); however, a trend towards less viable
tumor cells in patients with high
pazopanib concentrations in
tumor tissue was observed in a categorical analysis. Possible explanations for the lack of correlation might be heterogeneity of the
tumors and timing of the biopsy procedure.