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Key Clinical Summary: Evidence-based sequencing strategies for patients progressing on a first-line ARPI

This is a micro-learning module summary of a presentation by Dr. Emmanuel Antonarakis which you can find here. Before participating, please read our CME and disclosure information which can be found here

This activity is supported by an independent medical educational grant from Pfizer. This online education program has been designed for healthcare professionals globally.

Introduction
This summary explores evidence‑based sequencing strategies for patients with metastatic castration‑resistant prostate cancer (mCRPC) who progress after first‑line androgen receptor pathway inhibitor (ARPI)‑based therapy, outlining the evolving treatment landscape, the role of biomarkers, and the integration of chemotherapy, poly ADP-ribose polymerase (PARP) inhibition, and radioligand therapy. It reviews clinical trial data supporting key therapeutic options and highlights how biomarker‑driven approaches can refine individualized treatment planning in the post‑ARPI setting.

Treatment Landscape After First‑Line ARPI Progression

  • Patients progressing on androgen-deprivation therapy (ADT) plus an ARPI transition into the post‑ARPI mCRPC setting, where multiple therapeutic classes are available.
  • Options include:
    • Docetaxel chemotherapy, the preferred next systemic therapy for most biomarker‑unselected patients.
    • PARP inhibitors for those with BRCA1/2 or broader homologous recombination repair (HRR) alterations.
    • 177Lu‑PSMA‑617 radioligand therapy for PSMA‑positive disease.
    • Sipuleucel‑T for asymptomatic or minimally symptomatic patients.
    • Radium‑223 for symptomatic bone‑predominant disease without visceral metastases.
    • Cabazitaxel/carboplatin for aggressive‑variant or neuroendocrine‑like prostate cancer.
  • Switching between ARPIs is discouraged due to cross‑resistance and limited clinical benefit.

Chemotherapy

  • Docetaxel remains the preferred next therapy for most patients progressing on first‑line ARPI.
  • Cabazitaxel is typically used after docetaxel but may be combined with carboplatin in aggressive‑variant or neuroendocrine‑like prostate cancer.
  • Clinical features suggesting aggressive biology include:
    • Visceral metastases.
    • Low PSA relative to disease burden.
    • Lytic bone lesions.
    • Bulky nodal disease.
  • These patients may benefit from early incorporation of platinum‑based chemotherapy.

PARP Inhibitors for HRR‑Altered mCRPC

  • PARP inhibition is a key strategy for patients with deleterious BRCA1/2 or other HRR gene alterations.
  • TRITON3 evaluated rucaparib versus physician’s choice (docetaxel or ARPI switch) in BRCA1/2‑ or ATM‑mutated mCRPC after one prior ARPI. Compared with physician’s choice, rucaparib therapy demonstrated:
    • Improved radiographic progression-free survival (PFS; hazard ratio [HR] 0.61, 95% confidence interval [CI] 0.47–0.80; p<0.001)
    • This PFS improvement was also seen in the BRCA subgroup where docetaxel was the comparator (HR 0.53; 95% CI 0.37–0.77) and where 2nd-generation ARPIs were the comparator (HR 0.38; 95% CI 0.25–0.58)
  • Rucaparib and olaparib monotherapies for BRCA‑altered mCRPC are supported by level 1 evidence.
  • PARP inhibitor + ARPI combinations have weaker evidence in this setting because pivotal trials enrolled ARPI‑naïve patients.

Radioligand Therapy With 177Lu‑PSMA‑617

  • 177Lu‑PSMA‑617 delivers targeted beta radiation to prostate-specific membrane antigen (PSMA)‑expressing cells and is FDA‑approved for PSMA‑positive mCRPC.
  • PSMAfore compared 177Lu‑PSMA‑617 with ARPI switch in pre‑taxane mCRPC. Compared with ARPI switch, 177Lu‑PSMA‑617 demonstrated:
    • Significant improvement in radiographic PFS (HR 0.49; 95% CI 0.39–0.61).
    • Higher PSA response rates (51 vs 17%) and objective responses.
    • No overall survival (OS) difference (p=0.44), likely due to 84% crossover from ARPI switch to 177Lu‑PSMA‑617.
  • Common adverse events with the radioligand included dry mouth, asthenia, nausea, and anemia.
  • PLUDO, a Canadian randomized phase 2 trial, compared docetaxel → 177Lu‑PSMA‑617 versus 177Lu‑PSMA‑617 → docetaxel:
    • There was no difference between sequences in first radiographic PFS (p=0.51).
    • OS favored the sequence beginning with docetaxel (median 18.2 months vs 14.3 months; HR 1.64, 95% CI 1.14–2.35; p=0.02), suggesting potential sequencing effects.

Immunotherapy and Radiopharmaceuticals

  • Sipuleucel‑T remains an option for asymptomatic or minimally symptomatic patients without visceral disease.
  • Radium‑223 is appropriate for symptomatic bone‑predominant disease without visceral metastases.
  • These agents may be integrated into sequencing strategies depending on symptom burden and disease distribution.

Biomarker‑Driven Treatment Selection

  • PSMA PET imaging is essential for selecting patients for 177Lu‑PSMA‑617.
  • ctDNA fraction provides prognostic information:
    • Higher ctDNA levels correlate with worse outcomes across treatment arms.
    • In PSMAfore, ctDNA was prognostic but not predictive.
  • In TheraP, ctDNA analyses suggested potential predictive value for PFS and OS:
    • ctDNA <2% may favor 177Lu‑PSMA‑617 over cabazitaxel.
    • ctDNA ≥30% may favor cabazitaxel.
  • PTEN loss in TheraP may predict greater OS benefit from 177Lu‑PSMA‑617 relative to cabazitaxel.
  • In PSMAfore, genomic alterations such as androgen-receptor (AR) amplification, TP53 mutation, and 8q (MYC) amplification were associated with poorer prognosis but were not predictive of radioligand therapy benefit.

Clinical Implications for Treatment Planning

  • Treatment selection after first‑line ARPI progression relies on clinical features, biomarkers, and imaging.
  • Docetaxel suits most patients, while platinum chemotherapy may benefit aggressive‑variant disease. PARP inhibitors or 177Lu‑PSMA‑617 fit offer targeted options for those with HRR mutations or PSMA‑positive disease
  • Applying these factors supports more individualized and effective treatment planning in the post‑ARPI, pre‑taxane mCRPC setting.

Conclusions

The post‑ARPI, pre‑taxane mCRPC landscape includes multiple effective therapeutic options, each informed by clinical presentation, genomic alterations, and imaging biomarkers. Docetaxel remains the foundational next‑line therapy, while PARP inhibitors and radioligand therapy provide targeted approaches for biomarker‑defined subgroups. Emerging data from ctDNA analyses and sequencing trials continue to refine treatment selection. Integrating these evolving insights into clinical practice supports more personalized and effective management of mCRPC.

Content is accurate as of the date of release on 2 March 2026.