Validation of circulating steroid hormone measurements across different matrices by liquid chromatography-tandem mass spectrometry

Background: Steroid hormones are essential signalling molecules in prostate cancer (PC). However, many studies focusing on liquid biomarkers fail to take the hormonal status of these patients into account. Steroid measurements are sensitive to bias caused by matrix effects, thus assessing potential matrix effects is an important step in combining circulating tumour DNA (ctDNA) analysis with hormone status. Methods: We investigated the accuracy of multi-steroid hormone profiling in mechanically-separated plasma (MSP) samples and in plasma from CellSave Preservative (CS) tubes, that are typically used to obtain ctDNA, compared to measurements in serum. We performed multiplex steroid profiling by liquid chromatography-tandem mass spectrometry (LC-MS/MS) in samples obtained from ten healthy controls and ten castrationresistant prostate cancer (CRPC) patients. Results: Steroid measurements were comparable between MSP and serum. A small but consistent decrease of 8-21% compared to serum was observed when using CS plasma, which was considered to be within the acceptable margin. The minimal residual testosterone levels of CRPC patients could be sensitively quantified in both MSP and CS samples. Conclusions: We validated the use of MSP and CS samples for multi-steroid profiling by LC-MS/MS. The optimised use of these samples in clinical trials will allow us to gain further insight into the steroid metabolism in PC patients.