Liquid Biopsy Holds Promise in Prostate Cancer Diagnosis

Given the shortcomings of conventional biopsy, liquid biopsy offers a different strategy as a cutting-edge diagnostic tool.¹ By examining the circulating blood components, it is possible to assess the limiting factors more accurately for better treatment choices—clonal variations and heterogeneity. Additionally, liquid biopsy provides a more accurate representation of the genetic profile of patient tumor subclones. Cell-free DNA (cfDNA), circulating tumor cells (CTCs), cell-free proteins, exosomes, microRNAs, long noncoding RNAs, messenger RNAs, and peptides are among the molecules found in liquid biopsy that have potential clinical applications. CTCs and circulating tumor DNA (ctDNA) have been investigated to identify genome changes in prostate cancer (PCa) and track the evolving differential genomic landscape.¹ However, low concentrations of ctDNA in early cancer could limit liquid biopsy’s use in diagnosing some cancers early.² Because ctDNA from a specific tumor may exist in extremely low percentages, a liquid biopsy assay has the potential of missing important genetic modifications in early disease states. In rare circumstances, age-related clonal hematopoiesis of indeterminate potential can obstruct ctDNA testing, lead to incorrect results interpretation, and influence the care of patients.³

Joshua M. Lang, MD, MS

Associate Professor

Division of Hematology, Medical Oncology, and Palliative Care Department of Medicine

University of Wisconsin School of Medicine and Public Health Director

Circulating Biomarker Core and Liquid Biospecimen Team Coleader

Tumor Microenvironment Program

University of Wisconsin Carbone Cancer Center

Madison, W

According to Joshua M. Lang, MD, MS, associate professor, Division of Hematology, Medical Oncology, and Palliative Care, Department of Medicine, University of Wisconsin School of Medicine and Public Health and University of Wisconsin Carbone Cancer Center in Madison, Wisconsin, the importance of molecular understanding, especially in initially focusing on the genetics of PCa and how that can inform new therapies, has been one of the revolutions in PCa. There have been incredible advances during the past 5 years to identify other molecular changes, looking at genes that are turned on or off, and how that can also drive resistance to the different therapies available.

“We recently had a publication in The Journal of Clinical Investigation where we developed and validated a new liquid biopsy to look at these gene expression changes,” Lang said in an interview with Targeted Therapies in Oncology™.⁴ “Within that approach, we were able to identify the development of neuroendocrine or small cell prostate cancers. Some of the most aggressive cancers that are out there that our patients are fighting, we were able to identify with liquid biopsies, with an almost perfect accuracy,” Lang said.⁴ Liquid biopsy could recognize alterations that may identify metastatic potential of tumors^.5 Invasive traditional tissue samples represent a single time point in an ever-changing process and do not provide data on the evolution of tumor pathophysiology. Less invasive liquid biopsy could provide regular molecular monitoring for patients with inaccessible metastatic lesions or those who refuse repeat biopsies.⁵

New technologies have been developed to find mutations and chromosomal rearrangements in ctDNA, such as digital polymerase chain reaction (PCR)-based approaches.¹ Digital PCR is used to detect ctDNA in more than 75% of patients with advanced cancer, compared with a range of 48% to 73% in patients with localized tumors.¹ When compared with a tissue biopsy method, the use of ctDNA gives patients a viable clinical strategy with less discomfort and invasiveness.¹

Sanger sequencing, pyrosequencing, and next-generation sequencing (NGS) are the sequencing methods used.⁶ NGS has an edge over other approaches because of its sensitivity, which is 10 times higher. As a result, it is the most popular sequencing method for ctDNA detection, which makes up less than 1% of the overall cfDNA pool.⁶ The cost of NGS has significantly decreased from around $1 million per human genome in 2007 to less than $1000 today. NGS costs are expected to continue to decrease as access increases (FIGURE).⁷

Plasma DNA from patients with PCa can be utilized for whole-genome sequencing to identify mutations and copy number variations that can be used to infer clonal dynamics and longitudinal genome evolution in response to treatment.⁸

A developing biomarker for the early detection of relapse, genetic change in ctDNA offers the potential to direct focused therapy.⁹ Droplet digital PCR is frequently used for ctDNA analysis; however, NGS enables multigene testing without requiring access to a tumor sample to discover target mutations.⁹

According to a recent Chinese study, patients with nonmetastatic PCa (nmPCa) had a lower mutation burden than those with metastatic PCa (mPCa).¹⁰ The RB1 alteration was missing in the nmPCa cohort but 7.9% of the metastatic castration-resistant PCa (mCRPCa) cohort had the RB1 mutation and 7.3% of the metastatic castration-sensitive PCa (mCSPCa) cohort had the RB1 mutation.¹⁰ Evidently, the mCRPCa cohort had enriched androgen receptor (AR) alteration. Both the mCSPCa group and the mCRPCa cohorts had higher rates of altered FOXA1, SPOP, BRCA2, CDK12, TP53, and PTEN genes.¹⁰

The most frequently modified genes in PCa are tumor suppressor genes (TSGs), which include RB1, TP53, and PTEN. Cooperative functional loss of these TSGs has been linked to a poor prognosis.⁶ Similarly to the Chinese study, studies show more TSG mutations present in mPCa compared with nmPCa, with 63% more TSG alterations in mCSPCa and 92% more TSG alterations found in mCRPCa vs only 39% more TSG alterations found in localized CSPCa.⁶ It was also found that the CSPCa patient cohort’s TSG variations were associated with earlier recurrence and inferior outcomes.⁶

PARP inhibitors have recently received significant attention for the treatment of mCRPCa.¹¹ Although PARP inhibition may be most beneficial for patients with PCa and BRCA1 or BRCA2 mutations, the level of effect appears to be substantially lowered in the case of most other homologous recombination gene mutations. In various stages of the disease, several PARP inhibitors are being developed in conjunction with standard therapy, such as chemotherapy, new hormone treatment, and α-particle emitters.¹¹ Due in part to the development of a unique therapeutic class that targets a particular molecular subtype of PCa, the recent approval of rucaparib (Rubraca) and olaparib (Lynparza), both in May 2020, represents much-needed progress in the treatment of mCRPCa.^12,13

To identify patients with mCRPCa who have homologous recombination repair (HRR) mutations, the FDA has approved the FoundationOne CDx and BRACAnalysis CDx tests as companion diagnostics.14 This enables these patients to receive treatment with the PARP inhibitor olaparib.11 Foundation Medicine Chief Executive Officer Brian Alexander, MD, MPH, said in a news release that the FoundationOne CDx test’s approval “underscores the value of comprehensive genomic profiling in [patients with] advanced cancer…as it validates our ability to identify alterations in the 14 HRR pathway genes within FoundationOne CDx’s 324-gene panel that indicate a patient may be eligible for treatment with olaparib, a process not previously available.”¹⁴ There have previously been few therapeutic choices available for patients with metastatic HRR-mutated CRPCa; therefore, this represents a significant advancement.¹⁴

The phase 3 PROfound clinical trial (NCT02987543) demonstrated the clinical efficacy of olaparib in mCRPCa.15Patients with mCRPCa and pathogenic DNA alterations in specific HRR genes who had progressed following treatment with either enzalutamide (Xtandi) or abiraterone acetate (Zytiga) were randomly assigned to receive either olaparib or treatment with physician’s choice. For each therapy arm, 2 predetermined cohorts were examined: cohort A contained patients who had DNA mutations in the BRCA1, BRCA2, and ATM genes. BRIP1, BARD1, CDK12, CHEK1, CHEK2, FANCL, PALB2, PPP2R2A, RAD51B, RAD51C, RAD51D, and RAD54L were among the genes altered in cohort B.¹⁵ Radiographic progression-free survival (rPFS) in cohort A was the primary end point.15The population’s overall rPFS, the objective response rate (ORR), and overall survival were important secondary end points.¹⁵

Olaparib significantly outperformed the control in cohort A, with a median rPFS of 7.4 months vs 3.6 months, respectively.¹⁵ In the entire population (cohorts A and B), rPFS was also improved with olaparib compared with the control; however, the extent of the benefit was attenuated, 5.8 months vs 3.5 months.¹⁵ The FDA approved olaparib for the treatment of patients with HRR-mutated mCRPCa (germline or somatic mutations in BRCA1/2, ATM, BRIP1, BARD1, CDK12, CHEK1, CHEK2, FANCL, PALB2, RAD51B, RAD51C, RAD51D, or RAD54L) who had previously received treatment with a novel AR-directed agent with or without prior taxane treatment based on PROfound.¹⁵

Based on the results of the single-arm TRITON2 clinical trial (NCT02952534), the FDA granted rucaparib accelerated approval for BRCA1/2-mutated mCRPCa in patients who have previously received an AR-directed therapy and a taxane chemotherapy.¹⁶ Patients with mCRPCa and HRR gene mutations who had progressed on taxane-based chemotherapy and next-generation AR treatment were eligible to participate. Patients received 600 mg of rucaparib twice daily.¹⁶

Patients must have either BRCA1, BRCA2, ATM, BARD1, BRIP1, CDK12, CHEK2, FANCA, NBN, PALB2, RAD51, RAD51B, RAD51C, RAD51D, or RAD54L pathogenic DNA mutations.

The ORR in RECIST-measurable patients and the prostate-specific antigen (PSA) response rate (50% or more reduction) in the total population, which included patients with RECIST nonmeasurable disease, were the primary end points.

A confirmed objective response was observed in 43% of patients.¹⁶ PSA response rates were seen in 55% of patients (n = 63/115) in the overall population.¹⁶

“One of the questions I see most from my patients in the clinic, when I talk about having to make a change in care to a new therapy or new trial, is ‘what are the chances this will work for me?’ Often, we just don’t have the tools to help us really answer that question beyond our clinical sense just on symptoms or radiographic findings. I think molecular information will be far more predictive and useful for our patients in decision-making,” explained Lang, who is also director of the University of Wisconsin Carbone Cancer Center’s circulating biomarker core and liquid biospecimen team and coleader of its tumor microenvironment program.

Lang spoke about the next steps in liquid biopsy. “I think that the focus needs to be on expanding this work, more collaboration with investigators evaluating PCa. We are extending this into other malignancies as well, including bladder and kidney cancer. I think what I am most excited about is the new opportunity to leverage information to identify new therapeutic targets. We’ve had incredible revolutions with new agents such as radioligand therapies that target prostate-specific membrane antigen and antibody-drug conjugates. We need to get them to the patients who express those targets and not just give targeted therapy to every patient. If we can identify those predictive biomarkers and can give patients the right therapy at the right time, that will speed up the drug approval process, improve quality of life, and give patients more time.”

REFERENCES

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11. Flippot R, Patrikidou A, Aldea M, et al. PARP inhibition, a new therapeutic avenue in patients with prostate cancer. Drugs. 2022;82(7):719-733. doi:10.1007/s40265-022-01703-5

12. FDA grants accelerated approval to rucaparib for BRCA-mutated metastatic castration-resistant prostate cancer. FDA. May 15, 2020. Accessed April 1, 2023. http://bit.ly/3ZXLcUK

13. FDA approves olaparib for HRR gene-mutated metastatic castration-resistant prostate cancer. FDA. Updated May 20, 2020. Accessed April 6, 2023. http://bit.ly/3Uro3sq

14. Foundation Medicine receives FDA approval for FoundationOne CDx as the companion diagnostic for Lynparza to identify patients with HRR-mutated metastatic castration-resistant prostate cancer. News release. Foundation Medicine. May 20, 2020. Accessed April 6, 2023. https://bwnews.pr/3KBvGIz

15. de Bono J, Mateo J, Fizazi K, et al. Olaparib for metastatic castration-resistant prostate cancer. N Engl J Med. 2020;382(22):2091-2102. doi:10.1056/NEJMoa1911440

16. Abida W, Patnaik A, Campbell D, et al; TRITON2 investigators. Rucaparib in men with metastatic castration-resistant prostate cancer harboring a BRCA1 or BRCA2 gene alteration. J Clin Oncol. 2020;38(32):3763-3772. doi:10.1200/JCO.20.01035