Moving Toward Personalized Care: Liquid Biopsy Predicts Response to Cisplatin in an Unusual Case of BRCA2-Null Neuroendocrine Prostate Cancer

Narrative review of challenges in the management of advanced neuroendocrine prostate cancer

With wide availability of potent androgen receptor targeted agents (ARTAs), the incidence of treatment-related neuroendocrine prostate cancer (t-NEPC) has been dramatically increasing. However, there is no standard effective treatment for this disease state. Recent advances in genomic and molecular medicine have identified some critical features of NEPC that would help in understanding the biology of the disease. Furthermore, invaluable pre-clinical in vivo and in vitro research models that represent NEPC have been developed. These advances in research have revealed a large heterogeneity of t-NEPC with varying degree of androgen receptor (AR), neuroendocrine (NE) marker, and cell cycle associated gene expressions, which may have clinical implication in terms of prognosis and treatment selection. Based on these studies, some potential drug targets have been identified, and early clinical trials are ongoing. In the future, more precise disease classification and biomarker-driven selection of patients will be critical for optimization of treatment for patients with NEPC. In the present review, we describe up-to-date findings of recent research on this topic and introduce ongoing therapeutic developments that are expected to lead to novel treatment strategies for NEPC in the future.

Molecular Testing Identifies Determinants of Exceptional Response and Guides Precision Therapy in a Patient with Lethal, Treatment-emergent Neuroendocrine Prostate Cancer

Nearly all prostate cancers start out as adenocarcinomas driven by the androgen receptor (AR). Neuroendocrine prostate cancer (NEPC) is a rare, AR-independent subtype with a poor prognosis and limited treatment options. Importantly, because of the widespread use of novel AR-targeting agents, the incidence of treatment-emergent (t)-NEPC is increasing in frequency. Molecular features commonly found in prostate adenocarcinomas are now well-recognized, including defects in homologous recombination (HR) genes, like breast cancer type 2 susceptibility protein (BRCA2), leading to increased sensitivity to deoxyribonucleic acid (DNA)-damaging agents (e.g., platinum chemotherapy or poly adenosine diphosphate-ribose polymerase (PARP) inhibitors). However, our own prior work demonstrates that HR gene defects are uncommon in t-NEPC. Herein, we describe a patient who originally presented with adenocarcinoma but who subsequently developed t-NEPC. Molecular testing determined that his t-NEPC tumor (but not his original adenocarcinoma) harbored complete copy number loss of BRCA2, as well as copy number loss of another HR gene - ataxia telangiectasia, mutated (ATM). Uncharacteristically for t-NEPC, the patient achieved a complete response to platinum chemotherapy. Based on emerging data for the role of maintenance PARP inhibitor therapy in ovarian cancer patients whose tumors harbor BRCA1/2 defects, we treated him with PARP inhibitor maintenance after chemotherapy. At nine months follow-up, the patient was still in complete remission. This report demonstrates the importance of molecular testing to clarify the biology of exceptional responders and to direct treatment. Our results also suggest that clinical trials of PARP inhibitor maintenance may be warranted in select patients with advanced prostate cancer, including those with t-NEPC, whose tumors harbor HR defects.

DNA repair defects in prostate cancer: impact for screening, prognostication and treatment

Failure of effective DNA damage repair is a hallmark of cancer, but was previously underappreciated as a driver of aggressive prostate cancer. However, recent international sequencing efforts have revealed that both germline and somatic alterations within the homologous recombination and mismatch repair pathways are relatively common in lethal metastatic disease. BRCA2 gene alterations are particularly prevalent and are linked to poor prognosis as well as poor responses to systemic therapy for castration-resistant prostate cancer, although there is conflicting support for the latter. Defective DNA repair contributes to tumour heterogeneity, evolution and progression, but there are high hopes that management of this aggressive subset will be transformed by biomarker-driven use of poly-ADP ribose polymerase (PARP) inhibitors and platinum-based chemotherapy. In this review, we detail the relationship between DNA repair defects and prostate cancer, highlighting the prevalence of mutations in key genes and their controversial association with clinical outcomes.

Predicting therapy response and resistance in metastatic prostate cancer with circulating tumor DNA

The treatment of metastatic castration-resistant prostate cancer (mCRPC) is empirical, with progress to a more precision medicine approach hampered by lack of predictive biomarkers. This is due in large part to the historical difficulty of molecularly profiling a bone-predominant metastatic disease. Focus has turned to minimally invasive sources of tumor material to better understand the molecular drivers of therapy resistance. Circulating cell-free tumor DNA (ctDNA) is highly abundant in the bloodstream of mCRPC patients and appears to provide an accurate snapshot of real-time tumor genomics. Already, the analysis of androgen receptor gene alterations in the ctDNA of mCRPC patient cohorts has suggested significant potential for guiding the use of androgen receptor-directed therapy. Furthermore, the monitoring of patient ctDNA burden in the wake of systemic therapy may offer a powerful surrogate for tracking tumor responses and emerging resistant subclones. This seminar covers recent advances in mCRPC patient ctDNA profiling, emerging associations of distinct molecular subtypes with clinical outcomes, and the potential for ctDNA to augment precision oncology.

Review of the clinical applications and technological advances of circulating tumor DNA in cancer monitoring

Circulating cell-free DNA (cfDNA) released by tumor cells, termed ctDNA, closely reflects the heterogeneity of primary cancers and their metastases. As a noninvasive, real-time monitoring biomarker, ctDNA is a promising tool for detecting driver gene mutations, assessing tumor burden and acquired resistance, and early diagnosis. However, isolation and enrichment of cfDNA is a big challenge due to the high degree of DNA fragmentation and its relatively low abundance in the bloodstream. This review aims to provide insights into the recent technological advances in acquisition of optimal quality cfDNA, the use of preservatives, isolation methods, processing timelines, and detection techniques. It also describes clinical applications of ctDNA in cancer patient management.

Clinical utility of emerging liquid biomarkers in advanced prostate cancer

The therapeutic landscape of advanced prostate cancer (PCa) has rapidly expanded in recent years. Despite significant improvements in patient overall survival, it remains challenging to determine the optimal therapy and sequence of therapies for individual patients. The development of molecular biomarkers will be key for patient stratification, and for monitoring response and resistance to therapy. In this context, minimally-invasive blood-based "liquid" biopsies are attractive as a practical surrogate for solid tumor tissue, providing a window into metastatic disease. Circulating tumor cells and circulating cell-free tumor DNA in particular have demonstrated remarkable potential to inform on PCa patient outcomes through the detection of specific genomic and transcriptomic alterations. This review covers recent advances in the development of clinically-informative liquid biomarkers for advanced PCa.

Treatment Outcomes and Tumor Loss of Heterozygosity in Germline DNA Repair-deficient Prostate Cancer

BACKGROUND

Germline mutations in DNA repair genes were recently reported in 8-12% of patients with metastatic castration-resistant prostate cancer (mCRPC). It is unknown whether these mutations associate with differential response to androgen receptor (AR)-directed therapy.

OBJECTIVE

To determine the clinical response of mCRPC patients with germline DNA repair defects to AR-directed therapies and to establish whether biallelic DNA repair gene loss is detectable in matched circulating tumor DNA (ctDNA).

DESIGN, SETTING, AND PARTICIPANTS

We recruited 319 mCRPC patients and performed targeted germline sequencing of 22 DNA repair genes. In patients with deleterious germline mutations, plasma cell-free DNA was also sequenced.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Prostate-specific antigen response and progression were assessed in relation to initial androgen deprivation therapy (ADT) and subsequent therapy for mCRPC using Kaplan-Meier analysis.

RESULTS AND LIMITATIONS

Of the 319 patients, 24 (7.5%) had deleterious germline mutations, with BRCA2 (n=16) being the most frequent. Patients (n=22) with mutations in genes linked to homologous recombination were heterogeneous at initial presentation but, after starting ADT, progressed to mCRPC with a median time of 11.8 mo (95% confidence interval [CI] 5.1-18.4). The median time to prostate-specific antigen progression on first-line AR-targeted therapy in the mCRPC setting was 3.3 mo (95% CI 2.7-3.9). Ten out of 11 evaluable patients with germline BRCA2 mutations had somatic deletion of the intact allele in ctDNA. A limitation of this study is absence of a formal control cohort for comparison of clinical outcomes.

CONCLUSIONS

Patients with mCRPC who have germline DNA repair defects exhibit attenuated responses to AR-targeted therapy. Biallelic gene loss was robustly detected in ctDNA, suggesting that this patient subset could be prioritized for therapies exploiting defective DNA repair using a liquid biopsy.

PATIENT SUMMARY

Patients with metastatic prostate cancer and germline DNA repair defects exhibit a poor response to standard hormonal therapies, but may be prioritized for potentially more effective therapies using a blood test.

Circulating Tumor Cells (CTC) and Cell-Free DNA (cfDNA) Workshop 2016: Scientific Opportunities and Logistics for Cancer Clinical Trial Incorporation

Despite the identification of circulating tumor cells (CTCs) and cell-free DNA (cfDNA) as potential blood-based biomarkers capable of providing prognostic and predictive information in cancer, they have not been incorporated into routine clinical practice. This resistance is due in part to technological limitations hampering CTC and cfDNA analysis, as well as a limited understanding of precisely how to interpret emergent biomarkers across various disease stages and tumor types. In recognition of these challenges, a group of researchers and clinicians focused on blood-based biomarker development met at the Canadian Cancer Trials Group (CCTG) Spring Meeting in Toronto, Canada on 29 April 2016 for a workshop discussing novel CTC/cfDNA technologies, interpretation of data obtained from CTCs versus cfDNA, challenges regarding disease evolution and heterogeneity, and logistical considerations for incorporation of CTCs/cfDNA into clinical trials, and ultimately into routine clinical use. The objectives of this workshop included discussion of the current barriers to clinical implementation and recent progress made in the field, as well as fueling meaningful collaborations and partnerships between researchers and clinicians. We anticipate that the considerations highlighted at this workshop will lead to advances in both basic and translational research and will ultimately impact patient management strategies and patient outcomes.

Cytotoxic and targeted therapy for hereditary cancers

There is a number of drugs demonstrating specific activity towards hereditary cancers. For example, tumors in BRCA1/2 mutation carriers usually arise via somatic inactivation of the remaining BRCA allele, which makes them particularly sensitive to platinum-based drugs, PARP inhibitors (PARPi), mitomycin C, liposomal doxorubicin, etc. There are several molecular assays for BRCA-ness, which permit to reveal BRCA-like phenocopies among sporadic tumors and thus extend clinical indications for the use of BRCA-specific therapies. Retrospective data on high-dose chemotherapy deserve consideration given some unexpected instances of cure from metastatic disease among BRCA1/2-mutated patients. Hereditary non-polyposis colorectal cancer (HNPCC) is characterized by high-level microsatellite instability (MSI-H), increased antigenicity and elevated expression of immunosuppressive molecules. Recent clinical trial demonstrated tumor responses in HNPCC patients treated by the immune checkpoint inhibitor pembrolizumab. There are successful clinical trials on the use of novel targeted agents for the treatment or rare cancer syndromes, e.g. RET inhibitors for hereditary medullary thyroid cancer, mTOR inhibitors for tumors arising in patients with tuberous sclerosis (TSC), and SMO inhibitors for basal-cell nevus syndrome. Germ-line mutation tests will be increasingly used in the future for the choice of the optimal therapy, therefore turnaround time for these laboratory procedures needs to be significantly reduced to ensure proper treatment planning.

Liquid biopsy: ready to guide therapy in advanced prostate cancer?

The identification of molecular markers associated with response to specific therapy is a key step for the implementation of personalised treatment strategies in patients with metastatic prostate cancer. Only in a low proportion of patients biopsies of metastatic tissue are performed. Circulating tumour cells (CTC), cell-free DNA (cfDNA) and RNA offer the potential for non-invasive characterisation of disease and molecular stratification of patients. Furthermore, a 'liquid biopsy' approach permits longitudinal assessments, allowing sequential monitoring of response and progression and the potential to alter therapy based on observed molecular changes. In prostate cancer, CTC enumeration using the CellSearch© platform correlates with survival. Recent studies on the presence of androgen receptor (AR) variants in CTC have shown that such molecular characterisation of CTC provides a potential for identifying patients with resistance to agents that inhibit the androgen signalling axis, such as abiraterone and enzalutamide. New developments in CTC isolation, as well as in vitro and in vivo analysis of CTC will further promote the use of CTC as a tool for retrieving molecular information from advanced tumours in order to identify mechanisms of therapy resistance. In addition to CTC, nucleic acids such as RNA and cfDNA released by tumour cells into the peripheral blood contain important information on transcriptomic and genomic alterations in the tumours. Initial studies have shown that genomic alterations of the AR and other genes detected in CTC or cfDNA of patients with castration-resistant prostate cancer correlate with treatment outcomes to enzalutamide and abiraterone. Due to recent developments in high-throughput analysis techniques, it is likely that CTC, cfDNA and RNA will be an important component of personalised treatment strategies in the future.