The PROTEUS Phase 3 Trial: Perioperative Apalutamide Changes a Decades-Old Treatment Paradigm in High-Risk Localized Prostate Cancer

KEY FINDINGS

• Trial: An international phase 3 randomized double-blind placebo-controlled trial in 2,109 patients (18 countries, 118 centres). Plenary presentation at ASCO 2026 (LBA1) with simultaneous publication in the NEJM.
• Pathological complete response: The rate of pathological complete response / minimal residual disease was 8.9% versus 1.0% (a ninefold increase; OR 10.17; p<0.0001).
• Metastasis-free survival: A 20% risk reduction in the apalutamide arm (HR 0.80; p=0.02); 5-year MFS rates were 78.2% versus 73.5%.
• Time to subsequent therapy: 74.2 months versus 41.5 months (HR 0.65; p<0.0001).
• Number of patients: 2,109 patients, median follow-up 61.7 months (~5 years).

Background and Clinical Need

High-risk localized or locally advanced prostate cancer represents a significant treatment challenge in urological practice. Radical prostatectomy is one of the standard curative approaches in this patient group; however, surgical outcomes often remain inadequate.

Studies show that approximately 50% of patients undergoing surgery with curative intent experience disease recurrence within 5 years, and that a substantial proportion of these patients face the risk of progressive disease and death. The standard approach of "operate first, then see" went unquestioned for decades.

Apalutamide, an androgen receptor inhibitor, is approved in the mCSPC and nmCRPC indications and has demonstrated an overall survival benefit in advanced prostate cancer. The PROTEUS trial evaluated this molecule at a much earlier stage of disease - in high-risk localized disease - with a perioperative approach.

Study Design

Patients with distant metastatic disease were excluded; patients underwent radical prostatectomy plus pelvic lymph node dissection. Both arms were followed after surgery according to protocol-defined follow-up.

Key Results

pCR: pathological complete response; MRD: minimal residual disease; EFS: event-free survival; HR: hazard ratio; OR: odds ratio

Safety Profile

The safety profile was consistent with previous apalutamide trials. The most frequent side effects were hot flush 63.4%, urinary incontinence 50.2% and erectile dysfunction 41.6%. The rate of grade 3-4 adverse events was 39.6% in the apalutamide arm and 31.0% in the placebo arm; treatment discontinuation due to side effects was reported as 7.4% and 2.7% respectively.

The great majority of patients returned to adequate testosterone levels within 8.1 months of treatment. Although the incidence of skin rash was higher in the apalutamide arm, mortality rates were similar between the two arms; deaths in the placebo arm were more frequently related to disease progression.

Implications for Clinical Practice

1. The concept of pre-surgical hormone blockade is now supported by phase 3 evidence

In high-risk localized prostate cancer, the concept of "pre-surgical hormone blockade plus androgen receptor inhibitor" is now supported by phase 3 evidence. The ninefold increase in pCR/MRD demonstrates the power of apalutamide in eliminating micrometastatic disease.

2. A long disease-free period

A median time to subsequent therapy of 74 months - that is, more than 6 years of additional time - means a genuinely disease-free period for patients.

3. Transfer from solid tumour practice to prostate cancer

These findings support the transfer to prostate cancer of the perioperative systemic treatment approach long applied in solid tumours such as breast and rectal cancer. Given that up to 50% of patients experience recurrence after radical prostatectomy, an effective treatment started before surgery is considered a potential new standard for the period ahead.

4. Approval process and guideline updates

Apalutamide has not yet received FDA/EMA approval in this indication and a submission process is expected shortly; current guideline updates should be followed. In many countries, including Türkiye, perioperative apalutamide is not yet within an approved indication. However, the plenary presentation of this trial at ASCO 2026 and simultaneous NEJM publication will accelerate updates in international guidelines.

5. The need for multidisciplinary coordination

How the combination of androgen deprivation and AR inhibition in the perioperative period is coordinated with the surgical approach requires multidisciplinary discussion.

Conclusion

The PROTEUS phase 3 trial is an important turning point with the potential to change a decades-old paradigm in the treatment of high-risk localized prostate cancer. The combination of apalutamide plus ADT before and after surgery offers meaningful and statistically robust benefits both in pathological response at surgery and in long-term metastasis-free survival.

These data clearly demonstrate that urology and medical oncology practice needs to intersect at an earlier stage and that a multidisciplinary approach in high-risk localized prostate cancer has now become an evidence-based necessity.

References

• Taplin ME, Gleave M, Shore ND, et al. Perioperative Apalutamide in High-Risk Localized Prostate Cancer. N Engl J Med. 2026. doi:10.1056/NEJMoa2603878
• Johnson & Johnson press release. ASCO 2026 PROTEUS final analysis. - jnj.com
• ASCO 2026 congress presentation. Oral Abstract #LBA1, Plenary Session, 31 May 2026, Chicago.
• PROTEUS trial registration. NCT03767244 - clinicaltrials.gov
• UroToday. Leading prostate cancer studies at ASCO 2026. - urotoday.com
• ASCO Post. PROTEUS Trial Suggests Perioperative Apalutamide May Improve Outcomes. - ascopost.com