Biomarkers In mCRPC Research Articles

Revealing metastatic castration-resistant prostate cancer master regulator through lncRNAs-centered regulatory network.

Metastatic castration-resistant prostate cancer (mCRPC) is an aggressive form of cancer unresponsive to androgen deprivation therapy (ADT) that spreads quickly to other organs. Despite reduced androgen levels after ADT, mCRPC development and lethality continues to be conducted by the androgen receptor (AR) axis. The maintenance of AR signaling in mCRPC is a result of AR alterations, androgen intratumoral production, and the action of regulatory elements, such as noncoding RNAs (ncRNAs). ncRNAs are key elements in cancer signaling, acting in tumor growth, metabolic reprogramming, and tumor progression. In prostate cancer (PCa), the ncRNAs have been reported to be associated with AR expression, PCa proliferation, and castration resistance. In this study, we aimed to reconstruct the lncRNA-centered regulatory network of mCRPC and identify the lncRNAs which act as master regulators (MRs). We used publicly available RNA-sequencing to infer the regulatory network of lncRNAs in mCRPC. Five gene signatures were employed to conduct the master regulator analysis. Inferred MRs were then subjected to functional enrichment and symbolic regression modeling. The latter approach was applied to identify the lncRNAs with greater predictive capacity and potential as a biomarker in mCRPC. We identified 31 lncRNAs involved in cellular proliferation, tumor metabolism, and invasion-metastasis cascade. SNHG18 and HELLPAR were the highlights of our results. SNHG18 was downregulated in mCRPC and enriched to metastasis signatures. It accurately distinguished both mCRPC and primary CRPC from normal tissue and was associated with epithelial-mesenchymal transition (EMT) and cell-matrix adhesion pathways. HELLPAR consistently distinguished mCRPC from primary CRPC and normal tissue using only its expression. Our results contribute to understanding the regulatory behavior of lncRNAs in mCRPC and indicate SNHG18 and HELLPAR as master regulators and potential new diagnostic targets in this tumor.

MFast-SeqS-based aneuploidy score in circulating cell-free DNA is a prognostic biomarker in prostate cancer.

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 (< 5 vs. ≥ 5) as well as CTC counts (< 5 vs. ≥ 5) in 131 mCRPC patients prior to treatment with cabazitaxel. We validated our findings in an independent cohort of 50 similarly treated mCRPC patients. We observed that, similar to the dichotomized CTC count [HR: 2.92; 95% confidence interval (CI);1.84-4.62], dichotomized aneuploidy scores (HR: 3.24; CI: 2.12-4.94) significantly correlated with overall survival in mCRPC patients. We conclude that a dichotomized aneuploidy score from cfDNA is a prognostic marker for survival in mCRPC patients within our discovery cohort and in an independent mCRPC validation cohort. Therefore, this easy and robust minimally-invasive assay can be readily implemented as a prognostic marker in mCRPC. A dichotomized aneuploidy score might also be used as a stratification factor in clinical studies to account for tumour load.

BRCA-deficient metastatic prostate cancer has an adverse prognosis and distinct genomic phenotype

Genomic alterations in DNA damage response (DDR) genes are common in metastatic castration-resistant prostate cancer (mCRPC). Understanding how these genomic events impact prognosis and/or treatment response is vital for optimising clinical outcomes. Targeted sequencing was performed on 407 plasma samples from 375 men with mCRPC. Using the CLIA-certified PredicineCARE™ cell-free DNA (cfDNA) assay, pathogenic alterations in 152 key genes (including 27 DDR-related genes) were assessed, as was the presence and mechanisms of biallelic loss in BRCA2. At least one DDR alteration was present in 34.5% (129/375) of patients (including monoallelic alterations). The most frequently altered DDR genes were BRCA2 (19%), ATM (13%), FANCA (5%), CHEK2 (5%) and BRCA1 (3%). Patients with BRCA alterations, especially BRCA2, had significantly worse progression-free survival (PFS) (Hazard ratio (HR) 3.3 [95% CI 1.9-6.0]; Cox regression p<0.001), overall survival (HR 2.2 [95% CI 1.1-4.5]; Cox regression p=0.02) and PSA response rates to androgen receptor (AR) pathway inhibitors (32% vs 60%, chi-square p=0.02). BRCA-deficient tumours were also enriched for alterations within multiple genes including in the AR and PI3K pathways. Zygosity of BRCA2 alterations had no discernible impact on clinical outcomes, with similarly poor PFS for monoallelic vs biallelic loss (median 3.9 months vs 3.4 months vs copy neutral 9.8 months). These data emphasise that the BRCA genes, in particular BRCA2, are key prognostic biomarkers in mCRPC. The clinical utility of BRCA2 as a marker of poor outcomes may, at least in cfDNA assays, be independent of the zygosity state detected. Enrichment of actionable genomic alterations in cfDNA from BRCA-deficient mCRPC may support rational co-targeting strategies in future clinical trials. Several funding sources have supported this study. A full list is provided in the Acknowledgments. No funding was received from Predicine, Inc. during the conduct of the study.

Increasing targeted therapy options for mCRPC patients using multigene NGS panel.

e17056 Background: Prostate cancer (PCa) represents the second most common malignancy in males, characterized by a high level of clinical and molecular heterogeneity. Eventually, many patients develop metastatic Castration Resistant Prostate Cancer (mCRPC). mCRPC refers to prostate cancer that has spread beyond the prostate gland and is associated with increased morbidity and mortality. Next Generation Sequencing (NGS) has led to the identification of genomic alterations that may represent actionable targets with therapeutic potential in mCRPC. Such alterations can be identified on the somatic or hereditary level and implicate a variety of cell cycle mechanisms, like the DNA repair mechanism (Homologous Recombination Repair genes and Mismatch Repair Genes), as well as the AR, mTOR/AKT/PI3K, PTEN, ERK/MEK/Raf/Ras and WNT signaling pathways. Methods: In this study, 75 samples of patients with mCRPC were successfully processed. An NGS panel, targeting 513 genes associated with molecular and immuno-checkpoint inhibitor therapies, was used for the detection of gene alterations and fusions. In addition, genetic markers such as TMB, MSI and %gLOH were calculated for a subset of patients. Results: At least one mutation was detected in almost 90% of the cases tested, including SNVs, CNVs and gene fusions in a broad spectrum of the tested genes. In our cohort, the most commonly altered gene was CDK12 (9.3%), followed by ATM (6.7%) and PIK3CA (5.3%). Mutations were also found in FANCA (2.7%) and PTEN (2.7%). TMB was calculated in 52 patients, out of which 9.5% were characterized as TMB high ( &gt; 10 muts/Mb). MSI status was high for 4.5% of patients and %gLOH was elevated in 37.5% of the tested cohort. A mutation in an HRR gene was found in 29% of patients, rendering them eligible for therapy with PARP inhibitors. In addition, 18.7% of the patients could benefit from off label treatment. The calculation of genetic biomarkers, like TMB, MSI, and LOH, led to an increase to the cohort of patients who could receive on label therapy, even in cases with no or non-targetable mutation on DNA or RNA level. Moreover, due to the continuous approval of new drug regimens, retrospective evaluation of tumor analysis results led to an increase of the percentage of patients that could benefit from targeted treatment by 20%. Conclusions: Our results indicate that tumor analysis is essential for the identification of actionable biomarkers in mCRPC, since more than half of the patients were positive for a biomarker related to either targeted therapy or immunotherapy. Hence, frequent re-evaluation of NGS results is essential due to continuous drug approvals.

A Compendium of AR Splice Variants in Metastatic Castration-Resistant Prostate Cancer

Treatment-induced AR alterations, including AR alternative splice variants (AR-Vs), have been extensively linked to harboring roles in primary and acquired resistance to conventional and next-generation hormonal therapies in prostate cancer and therefore have gained momentum. Our aim was to uniformly determine recurrent AR-Vs in metastatic castration-resistant prostate cancer (mCRPC) using whole transcriptome sequencing in order to assess which AR-Vs might hold potential diagnostic or prognostic relevance in future research. This study reports that in addition to the promising AR-V7 as a biomarker, AR45 and AR-V3 were also seen as recurrent AR-Vs and that the presence of any AR-V could be associated with higher AR expression. With future research, these AR-Vs may therefore harbor similar or complementary roles to AR-V7 as predictive and prognostic biomarkers in mCRPC or as proxies for abundant AR expression.

Plasma Exosomal AKR1C3 mRNA Expression Is a Predictive and Prognostic Biomarker in Patients with Metastatic Castration-Resistant Prostate Cancer.

Aldo-keto reductase family 1 member C3 (AKR1C3) is important in prostate cancer progression, being a potential biomarker in metastatic castration-resistant prostate cancer (mCRPC). Previous explorations of AKR1C3 are mainly based on tissue samples. This study investigates using plasma-based liquid biopsy to validate the prognostic and predictive value of AKR1C3 in patients with mCRPC . We prospectively recruited 62 patients with mCRPC. All patients received repeated prostate biopsies at the time of mCRPC diagnosis, and immunohistochemistry (IHC) staining was used to detect protein expression of AKR1C3 in the tissues. We took their blood simultaneously and performed digital droplet polymerase chain reaction (ddPCR) to measure expression levels of AKR1C3 in the exosomes. The detected plasma and tissue AKR1C3 expression levels were analyzed for patients' overall survival (OS) and progression-free survival under first-line abiraterone use (ABI-PFS). All other baseline characteristics were balanced between the 2 groups. 15/62 (24.2%) and 25/62 (40.3%) patients showed AKR1C3-EXO positive (≥20 copies/20 μL) and AKR1C3-IHC positive, respectively. Positive AKR1C3-EXO expression was associated with decreased patients' survival [ABI-PFS: 3.9 vs 10.1 months, P < .001; OS: 16.2 vs 32.5 months, P < .001]. AKR1C3-IHC positivity was also correlated with ABI-PFS and OS (P = .010, P = .016). In patients with worse baseline blood tests (including higher alkaline phosphatase (ALP) and lactate dehydrogenase (LDH) level and lower hemoglobin (HB) level), and lower ISUP/WHO group (<4), their OS was significantly worse when showing AKR1C3-EXO positive. AKR1C3-EXO is associated with patient prognosis regarding OS and ABI-PFS and can be used as a biomarker in mCRPC.

Androgen receptor genomic alterations and treatment resistance in metastatic prostate cancer

Genomic alterations to the androgen receptor (AR) are common in metastatic castration-resistant prostate cancer (mCRPC). AR copy number amplifications, ligand-binding domain missense mutations, and intronic structural rearrangements can all drive resistance to approved AR pathway inhibitors and their detection via tissue or liquid biopsy is linked to clinical outcomes. With an increasingly crowded treatment landscape, there is hope that AR genomic alterations can act as prognostic and/or predictive biomarkers to guide patient management. In this review, we evaluate the current evidence for AR genomic alterations as clinical biomarkers in mCRPC, focusing on correlative studies that have used plasma circulating tumor DNAto characterize AR genotype. We highlight data that demonstrates the complexity of AR genotype within individual patients, and suggest that future studies should account for cancer clonal heterogeneity and variable tumor content in liquid biopsy samples. Given the potential for cooccurrence of multiple AR genomic alterations in the same or competing subclones of a patient, it is distinctly challenging to attribute blanket clinical significance to any individual alteration. This challenge is further complicated by the varied treatment exposures in contemporary patients, and the fact that AR genotype continues to evolve in the mCRPC setting across sequential lines of systemic therapy. As treatment access and liquid biopsy technology continues to improve, we posit that real-time measures of AR biology are likely to play a key role in emerging precision oncology strategies for metastatic prostate cancer.

Prognostic and predictive utility of DNA damage response (DDR) aberrations detected in cell-free DNA (cfDNA) in metastatic castration-resistant prostate cancer (mCRPC).

153 Background: The prognostic significance of DDR alterations in mCRPC remains unclear, with conflicting data from prior reports. Whether DDR alterations are predictive of outcomes with therapeutic agents other than PARP inhibitors in mCRPC is also poorly understood. With increasing use of molecular profiling in mCRPC, understanding the full prognostic and predictive utility of plasma DDR alterations is paramount. Methods: A next-generation sequencing Predicine liquid biopsy assay was used to profile cfDNA and germline DNA in 407 mCRPC patients (pts) from two independent international cohorts (n=162 Australia, n=245 US). DDR genes profiled were BRCA2, ATM, BRCA1, MLH1 and MSH2. Kaplan-Meier survival estimates and multivariable Cox regression analyses were used to assess associations between DDR alterations and clinical outcomes including PSA response rate (PSA RR), progression-free survival and overall survival (OS). Results: Median age was 74 (IQR 67-79), with median follow up 74 months and median OS 23 months. 65/407 (16%) harboured pathogenic DDR alterations, including 21 patients with ³1 alteration. Frequency of genomic aberrations are shown in the table. BRCA2 alterations were further classified as heterozygous loss (66%), homozygous loss (14%), monoallelic mutation (11%) and biallelic mutation/loss of heterozygosity (9%). Aberrations in any DDR gene, ATM, MLH1 + MSH2 or BRCA2 were associated with shorter OS on univariable analysis, but only any DDR or BRCA2 aberration remained significant upon adjusting for clinical prognosticators and ctDNA fraction (Table). Pre-treatment BRCA2 aberration was associated with significantly shorter OS and lower PSA RR compared to BRCA2 wt for pts receiving an AR pathway inhibitor (ARPI) (18 vs 32 months, p=0.006; 36 vs 60%, p=0.04 respectively) but not for taxane chemotherapy (17 vs 20 months, p=0.3; 45 vs 66, p=0.1 respectively). Conclusions: Detection of an aberration in any DDR gene or BRCA2 was an independent poor prognostic factor across 2 large independent cohorts of mCRPC patients. Intriguingly, patients with a BRCA2 alteration appeared to have worse outcomes with ARPI but not chemotherapy, suggesting predictive utility of DDR profiling. Our data collectively speak to the potential role of DDR alterations, in particular BRCA2, as prognostic and/ or predictive biomarkers in mCRPC.[Table: see text]

Genomic Alterations to Guide Treatment Selection in Metastatic Prostate Cancer.

Treatment options for men with metastatic prostate cancer have greatly expanded in the last decade. Androgen receptor pathway inhibitors, taxane cytotoxic therapy, poly(ADP-ribose) polymerase inhibitors, and radionuclide theranostics against prostate-specific membrane antigen have collectively contributed to incremental improvements in both quality and longevity of life for patients with metastatic castration-resistant prostate cancer (mCRPC). Despite these successes, few studies inform on optimal therapy selection and sequencing across this crowded treatment landscape. Genomic analysis of both tissue and liquid biopsy specimens shows promise in bridging this practice gap, with alterations in several key prostate cancer driver genes demonstrating clear associations with clinical outcomes, as well as informing use of novel precision medicine targeted therapies. In this review, we evaluate the current evidence of genomic alterations in various oncogenic signaling pathways as clinical biomarkers in mCRPC, focusing on correlative studies that analyzed outcomes based on findings in plasma cell-free DNA. We highlight the pitfalls of interpreting genomic findings in samples with substandard tumor content, and suggest pathologic and disease factors to consider when embarking upon tumor genotyping to guide treatment decisions in metastatic prostate cancer. As access to life-prolonging therapies improves, and barriers to cost-effective genotyping and reliable data interpretation are overcome, we anticipate that predictive and prognostic biomarkers that inform on disease biology, drug sensitivity, and therapy resistance will inevitably be integrated into the routine care of patients with metastatic prostate cancer.

PTEN loss as a potential biomarker in patients with castration resistant prostate cancer M0.

e17043 Background: Until 2018, there were no approved agents for high risk non-metastatic castration-resistant prostate cancer (nmCRPC). Recently, three second-generation anti-androgens (apalutamide, enzalutamide and darolutamide), in combination with ADT, have demonstrated a significant benefit in metastasis-free survival (MFS) and overall survival.According to conventional imaging, nmCRPC state is the opposite to mCRPC. Nevertheless, CRPC is a continuous in which nmCRPC may share similar biology and biomarkers such as PTEN loss, which has proven to be a useful and targetable biomarker in mCRPC. Methods: We performed a prospective and multicenter analysis of 77 patients (pts) with nmCRPC. We collected blood samples as well as prostate cancer diagnostic biopsy whenever they were available. The aim of this study is to find potential biomarkers that could identify pts at a higher risk of metastasis development. Here we report preliminary results according to PTEN status. Results: We have analyzed 32 patients for PTEN loss. We report preliminary results using an IHC assay based on the IPATENTIAL150 PTEN score. Median age was 66 years and 50% of patients had a Gleason score &gt; 8 irrespectively of PTEN status. We identified 24 patients (75%) with PTEN loss with a median PSA at diagnosis of 13,1 ng/ml, and a PSA doubling time (PSA-DT) of 6,3 months vs. 37,35 ng/ml and 3,5 months respectively in the PTEN non-loss pts. In the PTEN loss population, 9 pts (37,5%) did not receive any local treatment vs. 2 pts in the PTEN non-loss (25%). Mediantime from diagnosis to CRPC was 11.5 vs 8.0 yrs in PTEN loss vs. non-loss pts. In the PTEN loss population 2 patients received apalutamide plus ADT and 2 darolutamide plus ADT, these patients were excluded for the MFS analysis. Median MFS was 37 months in the PTEN loss population vs. 23 months in the PTEN non-loss. However, with a median follow-up of 38 months, 54% of PTEN loss pts had developed metastasis and 50% of PTEN non-loss pts. Skeleton was by far the first site of metastasis in PTEN non-loss pts (75%), while PTEN loss pts developed metastasis in lymph nodes (38,5%) nearly as much as in the skeleton (46%). Conclusions: To our knowledge, this is the first data of PTEN loss as a biomarker in nmCRPC. In our study, PTEN loss in primary tumor is more frequent than previously documented for mCRPC. PTEN loss appears to provide a better prognosis and higher lymph node involvement. Further analysis will be performed to corroborate these results and identify other factors involved.

Feasibility study of gallium-68 citrate PET as a bone-tropic imaging biomarker in mCRPC.

31 Background: Transferrin receptor (TFRC) expression is controlled by the PI3K and MYC signaling pathways, which are frequently dysregulated in prostate cancer (PC). Gallium-68 citrate (68Ga-citrate) is an iron biomimetic, which can be used to image PC in a TFRC dependent fashion. We performed a single-center pilot imaging study to investigate the use of 68Ga-citrate PET in patients with metastatic castration-resistant PC (mCRPC). Methods: Following written informed consent, mCRPC patients were prospectively enrolled and underwent 68Ga-citrate PET imaging. Optional metastatic tumor biopsies were undertaken at the time of imaging. Results: 34 mCRPC patients underwent 68Ga-citrate PET imaging. The median age was 67.5 years old. Median duration of castration resistance was 17.5 months; 14.7% of patients were post-docetaxel. Median serum PSA was 35.2 ng/dL. A total of 483 lesions were detected on conventional imaging (CT, 99mTc-HDP) or 68Ga-citrate PET, including 420 osseous and 63 soft tissue (nodal and visceral) lesions (Table). 67.3% of all lesions were detected on 68Ga-citrate PET, including 74.5% of all osseous lesions but only 19.0% of all soft tissue lesions (p&lt;0.0001). Eight (1.7%) lesions were detected on 68Ga-citrate PET imaging only. Per-lesion average SUVmax (SUVmax,avg) was 6.7. Metastatic biopsies of PET avid lesions were performed in 20 patients (59%); adenocarcinoma histology was confirmed in 14 (70%) cases, treatment-emergent small cell neuroendocrine cancer (t-SCNC) in 6 (30%). There was no significant difference in SUVmax,avg between patients with adenocarcinoma or t-SCNC (SUVmax,avg 7.3 vs 7.6, respectively; Table). Serial 68Ga-citrate PET perfomed in a patient with biopsy-confirmed t-SCNC after 2 cycles of carboplatin/cabazitaxel demonstrated an early metabolic response (28.5% decrease in average SUVmax) confirmed on subsequent conventional imaging. Conclusions: 68Ga-citrate PET detects mCRPC bone metastases in patients with biopsy-proven prostatic adenocarcinoma or t-SCNC, distinguishing it from lineage dependent agents such as PSMA tracers. Detection of an early metabolic response in the bone of a treated t-SCNC patient was observed. Further prospective studies are ongoing coupling serial Ga-citrate PET with investigational agents targeting the MYC signaling pathway. Clinical trial information: NCT02391025. [Table: see text]

5-hydroxymethylcytosine as a liquid biopsy biomarker in mCRPC.

148 Background: 5-hydroxymethylcytosine (5hmC) is an epigenetic modification which regulates gene expression and is associated with active transcription. The optimization of 5hmC sequencing in cell-free DNA (cfDNA) could therefore enable assessment of gene activity through a liquid biopsy. We aimed to investigate the 5hmC landscape of metastatic castration-resistant prostate cancer (mCRPC) and to evaluate the potential of 5hmC modifications in cfDNA as biomarkers of outcome in mCRPC patients. Methods: Genome-wide 5hmC modifications were analyzed with a low-input whole-genome 5hmC sequencing method based on selective chemical labeling in DNA from 93 mCRPC tissue biopsies previously profiled with whole-genome sequencing (WGS), RNA-sequencing and whole-genome bisulfite sequencing (WGBS). In addition, we analyzed 64 cell-free DNA (cfDNA) samples, from men with mCRPC before first-line abiraterone or enzalutamide, with both 5hmC sequencing and a conventional targeted ctDNA panel assessing common genomic alterations. Results: In mCRPC tissue samples, 5hmC enrichment was more strongly associated with gene expression than promoter methylation or copy number. Among cancer hallmark pathways, the androgen response genes had the strongest association between 5hmC and gene expression, suggesting a disease specific marking of gene activation. 5hmC patterns in cfDNA could be used to estimate the circulating tumor DNA fraction (ct-fraction), which was prognostic for overall survival (tertiles of ct-fraction, HR = 1.6 95%CI 1.1-2.3, p = 0.007). Further, 5hmC levels were indicative of gain of oncogene activity (such as AR, MYC, and PIK3CA) and loss of tumor suppressor gene activity (such as RB1, TP53 and BRCA2). The number of alterations, by 5hmC levels, of common drivers of mCRPC was prognostic for overall survival, also after adjusting for ct-fraction (adjusted p = 0.00001), and the prognostic value of common alterations detected by 5hmC sequencing versus conventional targeted ctDNA sequencing was similar. Finally, 5hmC levels in cfDNA of genes not significantly altered by copy number gain or loss (and thus not routinely included in targeted ctDNA sequencing assays), such as TOP2A and EZH2, identified a high-risk subgroup of mCRPC, which was highly prognostic for overall survival independent of ct-fraction (adjusted HR = 1.8 95%CI 1.2-2.8, p = 0.007). Conclusions: 5hmC in mCRPC tissue demonstrated an association with gene expression that was highest for prostate cancer driver genes, highlighting the ability to track disease-specific biology. 5hmC in cfDNA from men with mCRPC can be used to estimate the ct-fraction of the sample, infer activity gain and loss of common drivers of mCRPC, and identify high-risk groups of mCRPC based on alterations not commonly detected with conventional ctDNA sequencing, showing its potential as a liquid biomarker. Further studies are aimed at optimizing and validating 5hmC-based biomarkers in larger cohorts.

HSD3B1 (1245A>C) germline variant and clinical outcomes in metastatic castration-resistant prostate cancer patients treated with abiraterone and enzalutamide: results from two prospective studies

A common polymorphism (1245A>C) in the HSD3B1 gene is associated with increased de novo synthesis of androgens and worse outcomes in men treated with androgen-deprivation therapy for metastatic castration-sensitive prostate cancer. The objective of the study was to determine whether this polymorphism is associated with outcomes for metastatic castration-resistant prostate cancer (mCRPC) treated with abiraterone or enzalutamide. A total of 547 patients treated with abiraterone or enzalutamide from two prospective cohorts were evaluated. The HSD3B1 genotype was determined by targeted sequencing and/or TaqMan single-nucleotide polymorphism genotyping. In cohort 1, patients were randomized to receive abiraterone+ prednisone or enzalutamide. In cohort 2, patients received either agent according to investigator's choice. Prostate-specific antigen (PSA) response rate, time to PSA progression (TTPP), time to progression (TTP) and overall survival were determined. Associations between HSD3B1 genotypes and outcomes were evaluated via univariate Cox regression. Multivariable Cox model was used to determine the independent association of each covariate. The HSD3B1 variant genotype (CC) was present in 15% of patients and was associated with worse TTP [hazard ratio (HR) 1.31, 95% confidence interval (CI) 1.02-1.67, P= 0.032] and PSA response rates (48% for CC versus 62% and 65% for AA and AC, respectively [P= 0.019]), with no significant difference in TTPP (HR 1.28, 95% CI 0.99-1.66, P= 0.064). The effect of genotype was similar for treatment with abiraterone or enzalutamide with a negative test for interaction for TTPP (P= 0.997) and TTP (P= 0.749). Multivariable analysis did not show a significant association between genotype and TTP or TTPP. The HSD3B1 (CC) genotype was associated with shorter TTP and lower PSA response rate in patients with mCRPC treated with abiraterone or enzalutamide. However, the CC genotype did not provide prognostic information beyond that conferred by standard clinical variables, suggesting that it may not be a suitable stand-alone biomarker in mCRPC.

Blood platelet volume predicts treatment-specific outcomes of metastatic castration-resistant prostate cancer

In the present guidelines for the management of metastatic castration-resistant prostate cancer (mCRPC), it is unclear who benefits most from androgen receptor axis-targeted agents (ARATs) or docetaxel as the first-line treatment. We conducted a retrospective study to explore new treatment-specific biomarkers in mCRPC. A total of 211 patients with mCRPC who received either ARAT or docetaxel as first-line treatment were included. Patients were compared for radiographic progression and prostate-specific antigen (PSA) progression. Multivariable Cox regression models were used to assess the association between pretreatment biomarkers and risk of events. The statistical interaction between biomarkers and clinical outcomes was also evaluated. Of all analyzed biomarkers, multivariable Cox regression models identified MPV [≤ median (9.7fL)] as an independent prognostic factor of radiographic progression [hazard ratio (HR), 2.35; 95% confidence interval (CI), 1.15-4.80; P = 0.019] and PSA progression (HR, 1.96; 95% CI, 1.01-3.95; P = 0.048) in patients treated with ARAT, whereas such associations were not observed in those treated with docetaxel. Interaction analyses showed that those initially treated with docetaxel have lower risk of radiographic progression (HR, 0.33; 95% CI, 0.13-0.79; P = 0.014) and PSA progression (HR, 0.48; 95% CI, 0.23-0.98; P = 0.044) than ARAT when MPV was small. The present study identified pretreatment MPV as a significant treatment-specific prognostic factor of PSA and radiographic progression in patients with mCRPC who received first-line treatment. Furthermore, our results suggested that those with small MPV may better be treated initially with docetaxel than ARAT.

HSD3B1 (1245A>C) polymorphism and clinical outcomes in metastatic castration-resistant prostate cancer (mCRPC) patients treated with abiraterone acetate (AA) and enzalutamide (ENZA): Results from two prospective studies.

5525 Background: The common HSD3B1 (1245A &gt; C) germline variant is associated with increased de-novo synthesis of androgens and worse outcomes in men treated with androgen-deprivation therapy in metastatic hormone sensitive prostate cancer. The aim of this study is to determine the role of this polymorphism on treatment outcomes for AA and ENZA in patients with mCRPC. Methods: A total of 547 patients treated with AA or ENZA for mCRPC from two prospective cohorts; cohort 1 included 202 from British Columbia (Canada) and cohort 2 enrolled 345 patients from the Spanish study PROREPAIR-B. HSD3B1 genotype was determined by targeted sequencing in cohort 1 and by Taqman SNP genotyping assay in cohort 2. Associations between HSD3B1 genotypes and (TTPP), time to progression (TTP) and overall survival (OS) were evaluated via univariate COX regression. Multivariate analysis was performed to determine the independent association of each covariate. Results: The proportions of patients with a homozygous wild-type HSD3B1 (AA), heterozygous (AC) and homozygous variant (CC) genotype were respectively 45.6%, 39.4% and 15%. As expected, known prognostic factors for mCRPC such as hemoglobin, alkaline phosphatase (ALP), LDH, PSA at baseline as well as site of metastasis were significantly associated with TTPP and TPP. In the combined cohort, HSD3B1 (CC) genotype was associated with worse TTP (HR 1.31, 95%CI 1.02-1.67, p = 0.032) and PSA response rates (48% for CC vs 62% and 65% for AA and AC, respectively (p = 0.019, χ²)). Similar trend was observed for TTPP (HR 1.28, 95%CI 0.99-1.66, p = 0.064). OS was not different among genotypes, but was significantly shorter for patients with CC genotype in cohort 1 (HR 1.97, 95%CI 1.14-3.40, p = 0.016). There was no association between HSD3B1 genotype and time to castration-resistance in either of the two cohorts. Multivariable analysis showed that LDH, ALP, hemoglobin and use of AA or ENZA as first-line therapy for mCRPC were independent prognostic factors for TTP and TTPP; non-significant association was observed for genotype and TTP. Conclusions: HSD3B1 homozygous variant genotype (CC) was associated with shorter TTP and lower PSA response rate in mCRPC patients treated with AA or ENZA. However, the CC genotype did not provide prognostic information beyond that conferred by standard clinical variables, suggesting that it may not be a suitable stand-alone biomarker in mCRPC.

Circulating tumor DNA fraction (ctDNA) as a surrogate predictive biomarker in metastatic castration-resistant prostate cancer (mCRPC).

5039 Background: Plasma ctDNA is a promising minimally invasive biomarker in mCRPC. Pre-treatment high levels of ctDNA reflect poor prognosis (Romanel et al, Sci Transl Med 2015; Annala et al, Cancer Discov 2018). However, the role of plasma ctDNA in prostate tumour monitoring is largely unexplored. We aimed to determine if monitoring tumour response by quantifying ctDNA levels in plasma could enable early assessment of therapy efficacy for mCRPC. Methods: Between January 2011 and June 2016, 132 sequential plasma samples from 54 mCRPC patients (pts) (30 pre- and 24 post-chemotherapy) treated with abiraterone (abi) were collected. Targeted next-generation sequencing was performed on the PGM Ion Torrent using a 316 or 318 Chip to account for 1000X expected coverage per target. We estimated the global tumour content for each sequential plasma sample from study patients by using the approach developed in (Carreira et al, Sci Trasl Med 2014; Romanel et al, Sci Transl Med 2015 ), which extends the CLONET framework (Prandi et al, Genome Biol 2014). Prostate Cancer Working Group -3 (PCWG3) criteria were used to assess clinical, biochemical (PSA) and radiographic (RAD) progression disease (PD). We considered ctDNA PD any increase of ctDNA from baseline value. Results: In our cohort of 54 pts (median age: 75 years, range 70-78), we observed 17 (31.5%) PD, 14 (25.9%) stable disease, and 23 (42.6%) partial/complete response after the first 3 months (mo) abi therapy. The odds ratio (OR) for PD having any increase in ctDNA and a PSA decline &lt; 50% at ~3-mo therapy was 10.83, 95% CI 2.55-45.95, P = 0.001, and 3.27, 95% CI 0.89-12.3, P = 0.074, respectively. In addition, we assessed all 3 types of median PD time from starting abi treatment, suggesting the ability of ctDNA variation to predict overall PD [RAD PD = 6.8 mo, PSA PD = 4.4 mo, and ctDNA PD = 3.0 mo, P = 0.008). An increase of ctDNA levels during the first 3-mo abi treatment was significantly associated with a long-term androgen deprivation therapy (ADT) before plasma sample collection (previous ADT &gt; 24 mo vs 12 &gt; previous ADT ≤23 mo vs &lt; 12 mo: P = 0.036). Conclusions: In mCRPC, an early change in ctDNA fraction may be considered as a predictive biomarker playing a key role in individualized disease monitoring. Prospective evaluation of treatment decisions based on ctDNA is now required.

Genomic predictors of benefit of docetaxel (D) and next-generation hormonal therapy (NHT) in metastatic castration resistant prostate cancer (mCRPC).

5018 Background: Predictive genomic biomarkers in mCRPC remain elusive. Prior studies suggest that tumor suppressor (TS) loss is prognostic, and may result in less benefit from NHT, but no impact on D efficacy. We assessed genomic predictors of differential benefit of androgen receptor-targeted therapy and chemotherapy for mCRPC. Methods: Patients with mCRPC and targeted exome sequencing of biopsies obtained after metastatic diagnosis were identified (n=109). Patients with pure small cell histology (n=6) were excluded. Time from NHT or D start to clinical/radiographic progression (time to treatment failure, TTTF) was estimated by Kaplan-Meier method, with censoring at next therapy or last follow-up for non-progressors. Results: 80.1% of patients had bone and/or lymph node-only metastases at mCRPC diagnosis. In total, 87/103 (84.5%) and 61/103 (59.2%) received NHT and D for mCRPC, respectively. Median overall survival was 4.5 years from first mCRPC. The frequency and predictive association of selected recurrently-altered genes are detailed in the table. PTEN alterations (alts) were associated with worse TTTF on NHT, but not D, and a similar trend was observed with BRCA2. Biallelic RB1 loss was strongly predictive, conferring significantly shorter TTTF on both NHT and D. A score based on presence of tumor PTEN alt (1) and/or biallelic RB1 alt (1) was predictive of TTTF on NHT (median TTTF of score 0 vs 1 vs 2: 14.7 vs 12 vs 3.8 months; log rank p=0.003). Conclusions: The presence of single or compound PTEN and RB1 alts predict poorer outcomes with NHT for mCRPC. Chemotherapy may be a preferred therapeutic strategy for this patient population. [Table: see text]

Plasma-based exploratory biomarker analysis to evaluate GT0918 in a phase I/II study in mCRPC patients.

279 Background: GT0918, a novel potent androgen receptor antagonist, has been evaluated in a ph 1/2 study in mCRPC patients for its safety and efficacy. Here using patient plasma samples, we explored cell-free DNA &amp; RNA-based biomarkers to assess their associations with clinical response of GT0918. Methods: Blood samples were prospectively collected from mCRPC patients at baseline, on- and after study during the trial. PredicinePLUS cfDNA+cfRNA assay, a 180-gene targeted NGS Panel, was used to detect genomic alterations in plasma. Statistical analyses were performed in R 3.5.1. Results: Genomic alterations were detected in all 50 blood samples. Top mutated genes are TP53 (52.5%) and AR (32.5%). When combing variants from genes in a signaling pathway, mutation rates in PI3K axis and homologous recombination pathway are 32.0% and 34.0% respectively. Importantly, AR hotspot mutations (W742C, T878A, and S889G) and amplifications are detected in multiple subjects at baseline, suggesting that it may be the driving events for resistance of prior therapies. AR splicing variants (AR-V3, AR-V7) and TMPRSS2-ERG fusion were also detected by cfRNA profiling. Interestingly, patient 001-001 harboring both AR W742C and T878A mutations detected in cfDNA with high mutation frequency didn’t carry corresponding mutations in cfRNA at the baseline but started to accumulate the mutations in C3D1. Patient 004-002 remained in the study with stable disease for 10 treatment cycles while having continuous increase of PSA. cfDNA profiling indicates frequency of prostate-specific SPOP mutation continued to decrease during the treatment. Conclusions: This is a preliminary analysis to explore potential predictive or pharmacodynamic biomarkers in mCRPC in response to GT0918 treatment. As an non-invasive assay, PredicinePLUS assay was able to detect genomic alterations in blood with a high sensitivity and provided useful molecular insights for treatment monitoring and drug sensitivity &amp; resistance mechanisms. Clinical trial information: NCT02826772.

Whole blood FOLH1 mRNA expression and treatment response in metastatic castration-resistant prostate cancer (mCRPC).

188 Background: Identifying predictive biomarkers for mCRPC patients receiving androgen receptor signalling inhibitors (ARSI) or chemotherapy remains an unmet clinical need. FOLH1 encodes for Prostate-Specific Membrane Antigen (PSMA), a type II glycoprotein highly expressed on prostate cancer cells. We designed a whole blood assay to detect FOLH1 mRNA, and correlated expression with clinical outcomes in patients commencing ARSI (abiraterone or enzalutamide) or chemotherapy (docetaxel or cabazitaxel). Methods: mCRPC patients commencing ARSI or chemotherapy were prospectively recruited at three Australian centres from June 2016 to July 2018. A quantitative reverse transcription polymerase chain reaction assay was used to detect FOLH1 transcript from whole blood samples collected in PAXgene® RNA tubes. Pre-treatment FOLH1 expression was correlated with PSA response rate (Fisher’s exact test) and PSA progression-free survival (PSA-PFS) (log-rank test). Results: Median follow-up was 13.6 months (IQR 9.7–19.3). In total, 88 pre-treatment samples were analysed, of which 75 (85%) were FOLH1-positive. In patients receiving ARSI, outcomes favoured FOLH1-positive patients compared to FOLH1-negative patients, with higher PSA response rates (39/60, 65% vs. 2/7, 29%; p = 0.1) and longer PSA-PFS (median 9.0 months [95% CI, 7.2-10.8] vs. 2.8 months [95% CI, 2.3-3.3]; p = 0.03). Conversely, in chemotherapy-treated patients, inferior outcomes were observed in FOLH1-positive patients compared to FOLH1-negative patients, with lower PSA response rates (4/15, 27% vs. 5/6, 83%, p = 0.05) and shorter PSA-PFS (median 2.9 months [95% CI, 2.8-3.0] vs. 4.1 months [95% CI, 3.7-4.5]; p = 0.32). Conclusions: Pre-treatment FOLH1 expression may differentiate between outcomes on ARSI vs. chemotherapy in mCRPC patients. The utility of FOLH1 as a predictive biomarker in mCRPC warrants further evaluation in larger, independent cohorts. [Table: see text]

Serum Free Methylated Glutathione S-transferase 1 DNA Levels, Survival, and Response to Docetaxel in Metastatic, Castration-resistant Prostate Cancer: Post Hoc Analyses of Data from a Phase 3 Trial

BackgroundGlutathione S-transferase 1 (GSTP1) expression is inactivated in >90% of all prostate cancers in association with aberrant DNA methylation. Detection of serum free methylated GSTP1 (mGSTP1) DNA is associated with overall survival (OS) and response to docetaxel in metastatic castration-resistant prostate cancer (mCRPC) in test and internal validation cohorts. ObjectiveTo assess the relationship between serum free mGSTP1 and treatment outcomes in SYNERGY, a phase 3 multicentre randomised trial testing the addition of custirsen to first-line chemotherapy with docetaxel in mCRPC. Design, setting, and participantsSerum free mGSTP1 DNA was measured by a sensitive methylation-specific polymerase chain reaction assay in paired samples (baseline and after two cycles of docetaxel) from 600 patients. Outcome measurements and statistical analysisAssociations between serum free mGSTP1 at baseline, change in mGSTP1 after docetaxel, OS, and time to prostate-specific antigen (PSA) progression were examined using Cox proportional hazards models and Kaplan-Meier methods. Results and limitationsSerum free mGSTP1 was detectable at baseline in 458 (81%) patients. Of those with detectable mGSTP1 at baseline, mGSTP1 became undetectable after two cycles in 243 (53%). Undetectable mGSTP1 at baseline was associated with longer OS (hazard ratio [HR] 0.4, 95% confidence interval [CI] 0.29–0.55; p<0.00001). The event of mGSTP1 becoming undetectable after two cycles of chemotherapy was associated with longer OS (HR 0.36, 95% CI 0.29–0.46; p<0.00001) and longer time to PSA progression (HR 0.44, 95% CI 0.35–0.56; p<0.00001). Associations between mGSTP1 and clinical outcomes were independent of other established prognostic variables. Analysis was limited by the lack of radiographic progression-free survival data. ConclusionsThis is the first study to externally validate the prognostic role of a circulating epigenetic biomarker in mCRPC. Further studies are needed to validate serum free mGSTP1 as a surrogate endpoint for clinical trials and as a potential clinical decision tool. Patient summaryIn this study, we confirmed that a blood marker predicted outcomes after chemotherapy for metastatic prostate cancer. This marker may accelerate future clinical trials of new therapies and be useful in the clinic to guide treatment decisions.