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Multiple prognostic biomarkers, including circulating tumour cell (CTC) counts, exist in metastatic castration‐resistant prostate cancer (mCRPC) patients, but none of them have been implemented into daily clinical care. The modified fast aneuploidy screening test‐sequencing system (mFast‐SeqS), which yields a genome‐wide aneuploidy score, is able to reflect the fraction of cell‐free tumour DNA (ctDNA) within cell‐free DNA (cfDNA) and may be a promising biomarker in mCRPC. In this study, we investigated the prognostic value of dichotomized aneuploidy scores (

Second‐line treatment with immune checkpoint inhibition in patients with metastatic urothelial cancer (mUC) has a low success rate (~ 20%). Circulating tumour‐derived DNA (ctDNA) levels may guide patient stratification, provided that an affordable and robust assay is available. Here, we investigate whether the modified fast aneuploidy screening test‐sequencing system (mFast‐SeqS) may provide such an assay. To this end, mFast‐SeqS was performed on cell‐free DNA (cfDNA) from 74 patients with mUC prior to treatment with pembrolizumab. Results were associated with corresponding tissue‐based profiles, plasma‐based variant allele frequencies (VAFs) and clinical response. We found that plasma‐derived mFast‐SeqS‐based aneuploidy scores significantly correlated with those observed in the corresponding tumour tissue as well as with the ctDNA level in the plasma. In multivariate logistic regression analysis, a high aneuploidy score was independently associated with lack of clinical benefit from treatment with pembrolizumab. In conclusion, mFast‐SeqS provides a patient‐friendly, high‐throughput and affordable method to estimate ctDNA level. Following independent validation, this test could be used to stratify mUC patients for response prior to the initiation of treatment with pembrolizumab.

The androgen receptor splice variant (AR‐V) 7 in circulating tumor cells (CTCs) is a predictor for resistance to anti‐AR‐targeted treatment, but not to taxane‐based chemotherapy in metastatic castration‐resistant prostate cancer (mCRPC). In this study, we investigated whether the presence of two constitutively active variants (AR‐V3, AR‐V7) and two other conditionally activated variants (AR‐V1, AR‐V9) vs full‐length androgen receptor (AR‐FL) measured in CTCs from patients with mCRPC were associated with outcome to therapy with the taxane cabazitaxel. Blood was collected at baseline and after two cycles of cabazitaxel from 118 mCRPC patients starting cabazitaxel in a prospective phase II trial. CellSearch‐enriched CTCs were enumerated and in parallel characterized for the presence of the AR‐Vs by reverse transcription quantitative polymerase chain reaction. Correlations with CTC and prostate‐specific antigen response to cabazitaxel as well as associations with overall survival (OS) were investigated. All AR‐Vs were frequently present and co‐expressed at frequencies of 31–48% at baseline and at 19–40% after two cycles of cabazitaxel. No specific directions of change in the measured variants were detected between the start of treatment and after two cycles of cabazitaxel. No associations between the presence of AR‐V3 and AR‐V7 and outcome to cabazitaxel were observed. While a reduction in CTCs to