Prostate Cancer in 2026: Personalizing ADT Duration, PARP Inhibitors Move Earlier, and a Bispecific That May Finally Crack Immunotherapy in This Disease

Prostate Cancer in 2026: Personalizing ADT Duration, PARP Inhibitors Move Earlier, and a Bispecific That May Finally Crack Immunotherapy in This Disease

Prostate cancer treatment is finally moving beyond broad strokes. In 2026, evidence is clarifying how long to use androgen deprivation therapy in high-risk localized disease, which patients benefit from PARP inhibitors in the hormone-sensitive metastatic setting, and whether a conditionally activated PSMA T-cell engager can do what immunotherapy has repeatedly failed to do in this disease. Dr. Li Zhang breaks down the key developments.

Table of Contents

1. Introduction: Precision Is Finally Coming to Prostate Cancer
2. ADT Duration in High-Risk Localized Disease
3. The PSMA PET Staging Question in Locally Advanced Disease
4. PARP Inhibitors in mHSPC: Selective, Not Universal
5. CAPItello-281: Capivasertib in PTEN-Deficient mHSPC
6. The mCRPC Landscape: Increasingly Complex, With a Promising New Direction
7. VIR-5500: A Conditionally Activated PSMA × CD3 T-Cell Engager
8. For Patients
9. Key Takeaways
10. References

Introduction: Precision Is Finally Coming to Prostate Cancer

Prostate cancer has long been treated with broad strokes—long courses of androgen deprivation therapy, empiric intensification, and systemic chemotherapy applied without clear biomarker selection. The field is finally moving toward a more individualized approach. Three areas define where prostate cancer treatment stands in 2026: how long to administer androgen deprivation therapy for localized high-risk disease, when and for whom PARP inhibitors belong in the hormone-sensitive metastatic setting, and an emerging T-cell engager platform that may represent the first immunotherapy to show genuine activity in this immunologically cold tumor type.

ADT Duration in High-Risk Localized Disease

Current NCCN guidelines recommend 12 to 36 months of androgen deprivation therapy (ADT) for high-risk localized prostate cancer—a range wide enough to offer little practical guidance. Two meta-analyses published in JAMA in 2022 and 2026, respectively, provide more useful direction [1,2].

For patients receiving external beam radiation therapy (EBRT) alone, longer ADT duration appears consistently more beneficial. The PROSPERO meta-analysis, with a median follow-up of 11.3 years, showed that 18 months of ADT reduced prostate cancer-specific mortality with a hazard ratio of approximately 0.75—a 25% risk reduction. Critically, beyond 18 months, the prostate cancer-specific mortality curve begins to flatten, while other-cause mortality increases with each additional month of ADT. The benefit-to-harm calculation shifts [2].

For patients receiving EBRT combined with a brachytherapy boost, a shorter duration of 12 months may be appropriate. The addition of a brachytherapy boost provides a more potent local dose, potentially reducing the required duration of systemic ADT needed to achieve cure [1].

Practical takeaways for ADT duration:

• 18 months is the minimum for high-risk patients receiving EBRT alone; longer duration may benefit very high-risk patients. Treatment should be personalized based on individual comorbidities.
• 12 months may be appropriate for patients receiving EBRT with a brachytherapy boost.
• Ongoing trials using the Decipher genomic classifier and incorporating androgen receptor pathway inhibitors (ARPIs; e.g., abiraterone, enzalutamide, apalutamide, darolutamide) may further refine the approach to ADT intensification or de-intensification.

The PSMA PET Staging Question

As PSMA PET scanning becomes more widely adopted, clinicians are increasingly encountering patients with PSMA-avid lymph nodes that would not have been detected—or staged as node-positive—on conventional imaging. This creates a new clinical category: PSMA node-positive disease without conventional imaging node positivity.

For young, fit patients with PSMA node-positive localized disease, data from the STAMPEDE trial (6-year follow-up) support treatment intensification in this population. Adding abiraterone/prednisone to ADT plus radiation improved all endpoints, including failure-free survival, metastasis-free survival, prostate cancer-specific survival, and overall survival [3]. In practice, 18 months of ADT combined with two years of abiraterone/prednisone (other ARPIs may be considered given Medicare Part D coverage and individual side effect profiles) is a reasonable approach for node-positive disease identified on PSMA staging.

PARP Inhibitors in Hormone-Sensitive Prostate Cancer: Selective, Not Universal

PARP inhibitors have been standard of care in metastatic castration-resistant prostate cancer (mCRPC) based on the PROfound, TALAPRO-2, TRITON2, MAGNITUDE, and PROPEL trials. More recently, PARP inhibitors have been incorporated into NCCN guidelines for the metastatic hormone-sensitive prostate cancer (mHSPC) setting, based on the AMPLITUDE study. The FDA approved niraparib specifically for BRCA2-mutant patients, supported by a hazard ratio of 0.5 for radiographic progression-free survival —a highly significant result representing a meaningful advance for this well-defined subset [4].

There is no clearly demonstrated benefit in non-BRCA HRR-deficient patients, a population not included in the FDA approval. For patients with de novo high-volume, high-risk BRCA2-mutant mHSPC, the question of whether to prioritize a PARP inhibitor–based triplet versus a docetaxel-based triplet remains unresolved and requires careful shared decision-making.

CAPItello-281: Capivasertib in PTEN-Deficient mHSPC

PTEN is a critical tumor suppressor gene whose loss activates the PI3K/AKT/mTOR pathway. PTEN deficiency is present in approximately 25–30% of castration-sensitive prostate cancer patients and becomes more prevalent as disease progresses. The CAPItello-281 study evaluated capivasertib (an AKT inhibitor) added to ADT/abiraterone/prednisone in patients with mHSPC who had PTEN deficiency, defined as ≥90% loss by immunohistochemistry [5].

The trial met its primary endpoint: radiographic progression-free survival improved by 7.5 months in the capivasertib arm. Subgroup analysis suggested that patients with higher degrees of PTEN loss (95–100% of cells) derived greater benefit than those at the 90% threshold. An FDA advisory committee voted 7–1 in favor of approval, suggesting regulatory approval is likely [5].

However, an overall survival benefit has not yet been demonstrated, and the toxicity profile warrants careful attention. On-target AKT inhibitor effects include diarrhea (grade 3 or higher in 6% of patients), rash (grade 3 or higher in 12% of patients), and hypoglycemia (grade 3 or higher in 10% of patients). A transient worsening of quality of life, particularly during the first three months of treatment, has also been observed [6].

Whether IHC-defined PTEN loss is the optimal selection strategy—compared with NGS-based assessment—remains an open question, as IHC is an imperfect assay for PTEN status.

The mCRPC Landscape: Increasingly Complex, With a Promising New Direction

The treatment algorithm for metastatic castration-resistant prostate cancer is already complex—encompassing ARPIs, docetaxel, cabazitaxel, PARP inhibitors, lutetium PSMA, and radium-223—and is becoming more so with emerging drug classes: AR degraders, CYP11 inhibitors, RIPTACs, T-cell engagers, antibody-drug conjugates (ADCs), radioligand therapies, CAR T cells, and selective PARP inhibitors. The challenge of treatment selection and sequencing in mCRPC is significant and growing.

Within this evolving landscape, one early-phase result stands out as potentially transformative.

VIR-5500: A Conditionally Activated PSMA × CD3 T-Cell Engager

Immunotherapy has repeatedly failed in prostate cancer. The tumor microenvironment is immunologically cold, checkpoint inhibitors produce minimal responses, and cytokine release syndrome has been a limiting toxicity with earlier bispecific approaches. VIR-5500 addresses both of these barriers through an elegant engineering solution [7].

VIR-5500 is a conditionally activated bispecific antibody prodrug that bridges PSMA (on tumor cells) to CD3 (on T cells)—the classical mechanism of T-cell engagers. The critical innovation is a cleavable protein mask that renders the molecule inactive in systemic circulation. This mask is cleaved only by proteases present in the tumor microenvironment, meaning the bispecific antibody becomes active specifically at the tumor site, thereby avoiding the systemic cytokine release syndrome that has limited T-cell engager development in this disease [7].

Phase 1 dose-escalation data were presented at ASCO GU 2026 in heavily pretreated mCRPC patients with significant disease burden. The findings are striking [7]:

• Responses were dose-dependent, with deeper responses observed at higher doses (3,000 µg/kg).
• PSA90 response rate: 53%; PSA99 response rate: 30%—in a late-stage, heavily pretreated population.
• PSA declines were detectable as early as cycle 1, day 8.
• No grade 3 or higher cytokine release syndrome was observed; CRS was minimal, consisting primarily of grade 1 fever; no ICANS occurred; no CRS prophylaxis was required.
• One patient with prior treatment across five lines—including actinium-225—experienced a PSA decline from 100 to 0.03. Tumor biopsy after four doses demonstrated T-cell infiltration, providing direct evidence of immune activation at the tumor site.
• Another patient who had failed all standard-of-care options achieved a complete response after 9 weeks of treatment.
• Some patients reported tumor pain shortly after infusion, further indicating T-cell activation at the site of disease.
• The durability of responses is preliminary but emerging.

Expansion cohorts in both late-line and earlier-line mCRPC are ongoing, with registration trials targeted for 2027. For a disease in which immunotherapy has consistently failed, this trial provided proof-of-concept that T cells can be directed to and activated within prostate tumors—a meaningful and exciting advance [7].

For Patients

Prostate cancer treatment is becoming more personalized, guided increasingly by the molecular characteristics of your specific tumor. If you have high-risk localized prostate cancer being treated with radiation, ask your oncologist how long you should receive androgen deprivation therapy and whether your specific situation warrants adding an ARPI such as abiraterone. If you have metastatic prostate cancer, ask about germline and tumor genetic testing for HRR gene mutations, including BRCA2—these results may make you eligible for PARP inhibitors that can meaningfully extend survival. And if you have castration-resistant prostate cancer that has progressed through multiple lines of therapy, ask about clinical trial opportunities—the VIR-5500 T-cell engager program is among the most promising early-phase developments in this space and may become available to patients in the near future.

Key Takeaways

• ADT duration for high-risk localized prostate cancer: 18 months is the minimum with EBRT alone; 12 months may suffice with a brachytherapy boost; beyond 18 months with EBRT alone, other-cause mortality rises while prostate cancer–specific benefit plateaus.
• PSMA node-positive localized disease: Intensification with abiraterone plus ADT plus radiation is supported by STAMPEDE trial 6-year overall survival data.
• PARP inhibitors in mHSPC: Effective in BRCA2-mutant patients (niraparib HR 0.5 for OS) and should not be applied broadly to unselected patients.
• CAPItello-281: Capivasertib improves radiographic progression-free survival by 7.5 months in PTEN-deficient mHSPC (IHC ≥90% loss); OS benefit not yet demonstrated; toxicity includes GI effects, rash, and hypoglycemia.
• VIR-5500: Conditionally activated PSMA × CD3 T-cell engager with tumor microenvironment–dependent activation avoids systemic CRS; PSA90 53%, PSA99 30% in heavily pretreated mCRPC; T-cell infiltration confirmed in tumor biopsies; registration trials planned for 2027.

Related Reading on The Cancer News

1. Interpreting Bladder Cancer Abstracts at GU ASCO 2026 for Real-World Practice
2. The Hidden Barrier to Precision Oncology: How Insurance Policies Delay Access to Genomic Testing
3. The Immunotherapy Landscape in Colorectal Cancer: Where We Stand and Where We’re Headed

References

[1] Kishan AU, Steigler A, Denham JW, Zapatero A, Guerrero A, et al. Interplay between duration of androgen deprivation therapy and external beam radiotherapy with or without a brachytherapy boost for optimal treatment of high-risk prostate cancer: a patient-level data analysis of 3 cohorts. JAMA Oncol. 2022.

[2] Zaorsky NG, et al. Optimal duration of androgen deprivation therapy with definitive radiotherapy for localized prostate cancer: a meta-analysis. JAMA. 2026.

[3] Attard G, Murphy L, Clarke NW, Sachdeva A, Jones CA, et al. Abiraterone acetate plus prednisolone with or without enzalutamide for patients with metastatic prostate cancer starting androgen deprivation therapy: final results from two randomised phase 3 trials of the STAMPEDE platform protocol. Lancet Oncol. 2023.

[4] Attard G, Agarwal N, Graff JN, Sandhu S, Efstathiou E, et al. Niraparib and abiraterone acetate plus prednisone for HRR-deficient metastatic castration-sensitive prostate cancer: a randomized phase 3 trial. Nat Med. 2025.

[5] Fizazi K, et al. Capivasertib plus abiraterone in PTEN-deficient metastatic hormone-sensitive prostate cancer: CAPItello-281 phase III study. Ann Oncol. 2026.

[6] George DJ, et al. Patient-reported outcomes (PRO) and tolerability of capivasertib (capi) plus abiraterone (abi) versus placebo (pbo) plus abi in patients (pts) with PTEN-deficient metastatic hormone-sensitive prostate cancer (mHSPC): CAPItello-281. J Clin Oncol. 2026.

[7] De Bono JS, et al. Preliminary phase 1 dose escalation results of VIR-5500 (AMX-500), a dual-masked PRO-XTEN T-cell engager, in metastatic castration-resistant prostate cancer (mCRPC). Presented at ASCO GU. 2026.

[8] Zhang L. Prostate Cancer Updates. Presented at the 2026 Alaska Hematology Oncology Conference, Anchorage, AK. May 2026.

About the Author

Li Zhang, MD, is a medical oncologist at Northwest Medical Specialties in the Pacific Northwest, specializing in genitourinary malignancies with a focus on prostate, bladder, and kidney cancers. She is actively involved in clinical research evaluating novel therapeutic approaches for GU cancers, including trials examining next-generation radioligand therapies and emerging immunotherapy strategies.