Genomic Profiles of De Novo High- and Low-Volume Metastatic Prostate Cancer: Results From a 2-Stage Feasibility and Prevalence Study in the STAMPEDE Trial

PURPOSE

The STAMPEDE trial recruits men with newly diagnosed, high-risk, hormone-sensitive prostate cancer. To ascertain the feasibility of targeted next-generation sequencing (tNGS) and the prevalence of baseline genomic aberrations, we sequenced tumor and germline DNA from patients with metastatic prostate cancer (mPCa) starting long-term androgen-deprivation therapy (ADT).

METHODS

In a 2-stage approach, archival, formalin-fixed, paraffin-embedded (FFPE) prostate tumor core biopsy samples were retrospectively subjected to 2 tNGS assays. Prospective enrollment enabled validation using tNGS in tumor and germline DNA.

RESULTS

In stage 1, tNGS data were obtained from 185 tumors from 287 patients (65%); 98% had de novo mPCa. We observed PI3K pathway aberrations in 43%, due to PTEN copy-number loss (34%) and/or activating mutations in PIK3 genes or AKT (18%) and TP53 mutation or loss in 33%. No androgen receptor (AR) aberrations were detected; RB1 loss was observed in < 1%. In stage 2, 93 (92%) of 101 FFPE tumors (biopsy obtained within 8 months) were successfully sequenced prospectively. The prevalence of DNA damage repair (DDR) deficiency was 14% (somatic) and 5% (germline). BRCA2 mutations and mismatch repair gene mutations were exclusive to high-volume disease. Aberrant DDR (22% v 15%), Wnt pathway (16% v 4%), and chromatin remodeling (16% v 8%) were all more common in high-volume compared with low-volume disease, but the small numbers limited statistical comparisons.

CONCLUSION

Prospective genomic characterization is feasible using residual diagnostic tumor samples and reveals that the genomic landscapes of de novo high-volume mPCa and advanced metastatic prostate cancer have notable similarities (PI3K pathway, DDR, Wnt, chromatin remodeling) and differences (AR, RB1). These results will inform the design and conduct of biomarker-directed trials in men with metastatic hormone-sensitive prostate cancer.

Abiraterone in "High-" and "Low-risk" Metastatic Hormone-sensitive Prostate Cancer

BACKGROUND

Abiraterone acetate received licencing for use in only "high-risk" metastatic hormone-naïve prostate cancer (mHNPC) following the LATITUDE trial findings. However, a "risk"-related effect was not seen in the STAMPEDE trial. There remains uncertainty as to whether men with LATITUDE "low-risk" M1 disease benefit from androgen deprivation therapy (ADT) combined with abiraterone acetate and prednisolone (AAP).

OBJECTIVE

Evaluation of heterogeneity of effect between LATITUDE high- and low-risk M1 prostate cancer patients receiving ADT + AAP in the STAMPEDE trial.

DESIGN, SETTING, AND PARTICIPANTS

A post hoc subgroup analysis of the 2017 STAMPEDE "abiraterone comparison". Staging scans for M1 patients contemporaneously randomised to ADT or ADT + AAP within the STAMPEDE trial were evaluated centrally and blind to treatment assignment. Stratification was by risk according to the criteria set out in the LATITUDE trial. Exploratory subgroup stratification incorporated the CHAARTED criteria.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

The primary outcome measure was overall survival (OS) and the secondary outcome measure was failure-free survival (FFS). Further exploratory analysis evaluated clinical skeletal-related events, progression-free survival (PFS), and prostate cancer-specific death. Standard Cox-regression and Kaplan-Meier survival estimates were employed for analysis.

RESULTS AND LIMITATIONS

A total of 901 M1 STAMPEDE patients were evaluated after exclusions. Of the patients, 428 (48%) were identified as having a low risk and 473 (52%) a high risk. Patients receiving ADT + AAP had significantly improved OS (low-risk hazard ratio [HR]: 0.66, 95% confidence interval or CI [0.44-0.98]) and FFS (low-risk HR: 0.24, 95% CI [0.17-0.33]) compared with ADT alone. Heterogeneity of effect was not seen between low- and high-risk groups for OS or FFS. For OS benefit in low risk, the number needed to treat was four times greater than that for high risk. However, this was not observed for the other measured endpoints.

CONCLUSIONS

Men with mHNPC gain treatment benefit from ADT + AAP irrespective of risk stratification for "risk" or "volume".

PATIENT SUMMARY

Coadministration of abiraterone acetate and prednisolone with androgen deprivation therapy (ADT) is associated with prolonged overall survival and disease control, compared with ADT alone, in all men with metastatic disease starting hormone therapy for the first time.

Targeted next-generation sequencing (tNGS) of metastatic castrate-sensitive prostate cancer (M1 CSPC): A pilot molecular analysis in the STAMPEDE multi-center clinical trial

5019

Background: The STAMPEDE trial recruits men with high risk prostate cancer commencing first line systemic therapy. In a pilot study to ascertain the feasibility of tNGS and the prevalence of common genomic aberrations, we tested a commercial clinically-accredited assay on tumor blocks and present data obtained in the largest cohort of treatment-naïve M1 CSPC to date. Methods: Archival FFPE blocks were retrieved from trial participants and a single block submitted for sequencing by a Foundation Medicine. Inc. tNGS assay that includes 395 genes. Results: We successfully obtained tNGS data on 115 (62%) of 186 patients enrolled between Nov-2011 and April-2017 at 15 UK participating centers. The median age was 70 years (IQR 44-85); 97% had de novo M1 disease and 83% Gleason score ≥8. We observed PTEN deficiency (34%) due to copy-number loss (25%) or mutation (9%); TP53 mutation or loss (33%) and aberrations in PI3K signaling (16%), genes involved in DNA repair (14%), Wnt signaling (14%) and cell cycle control (6%). In total, these aberrations were observed in 76% of patients, with 35% harboring two or more. No androgen receptor ( AR) mutations were detected. Conclusions: The prevalence of PTEN deficiency is comparable with that observed in mCRPC consistent with this being a feature of metastatic disease. In contrast, AR mutations are not observed in this treatment-naïve group. The prevalence of DNA repair deficiency is less than observed in mCRPC but more than reported in prostatectomy cohorts. Although it is possible to use FFPE biopsies for tNGS, the test failure-rate poises challenges to evaluating treatments in low prevalence biomarker-defined groups. These data will inform the design and conduct of biomarker-directed trials.