New Prostate Cancer Data From ASCO 2026: PROTEUS, TALAPRO-3, and Treatment Holidays

Introduction

Three trials presented at the 2026 ASCO Annual Meeting are reshaping how clinicians approach prostate cancer at nearly every stage of the disease, from high-risk localized disease being considered for surgery, to metastatic hormone-sensitive disease with genomic alterations, to the practical question of whether long-term androgen deprivation therapy (ADT) can ever safely pause. Together, PROTEUS, TALAPRO-3, and A-DREAM speak to a broader shift in the field: treatment intensity is increasingly being matched to individual risk and response, rather than applied uniformly.

PROTEUS Sets a New Bar for High-Risk Localized Disease

The PROTEUS trial addressed a scenario familiar to anyone managing high-risk localized or locally advanced prostate cancer (HR-LPC): should systemic therapy be layered around radical prostatectomy, and if so, does it change outcomes that matter to patients?

This phase 3, randomized, double-blind, placebo-controlled trial enrolled 2,109 patients with HR-LPC, randomizing them 1:1 to six cycles of neoadjuvant apalutamide (240 mg daily) plus ADT followed by radical prostatectomy and six cycles of adjuvant apalutamide plus ADT, versus placebo plus ADT on the same schedule. Baseline characteristics were well balanced, with a median age of 66 years in both arms; 95% of patients had Gleason scores of 8 or higher, and 12% had node-positive disease at baseline, confirming this was a genuinely high-risk population.

The trial was designed with two co-primary endpoints, and both were met. Pathologic complete response or minimal residual disease (defined as either no identifiable tumor or a residual tumor of no more than 5 mm confined to the prostate) at prostatectomy occurred in 8.9% of patients on apalutamide plus ADT versus 1.0% on placebo plus ADT, an odds ratio of 10.17 (95% CI, 5.27–19.64; P<.001), a roughly ninefold improvement. A disease stage of ypT0 was reached in 5.1% of the apalutamide group versus 0.4% of the placebo group. Metastasis-free survival, assessed by conventional imaging or PSMA-PET, also favored the apalutamide arm, with a 20% reduction in the risk of metastasis or death (HR, 0.80; 95% CI, 0.67–0.96; P=.02). The probability of metastasis-free survival at 5 years was 78.2% in the apalutamide group versus 73.5% in the placebo group. Notably, the trial was amended to incorporate PSMA-PET into MFS assessment as that imaging modality became standard, and post hoc analysis showed that approximately 65% of patients in the apalutamide group and 72% in the placebo group underwent PSMA PET at least once. Among MFS endpoint events, the majority of distant metastases were identified by PSMA PET (53% in the apalutamide group and 61% in the placebo group).

Several secondary endpoints reinforced the primary findings. Event-free survival improved by 29% (HR, 0.71; 95% CI, 0.63–0.80; P<.001), with a median of 57.1 months versus 38.4 months. Time to first subsequent therapy was significantly extended (median 74.2 months vs. 41.5 months; HR, 0.65; 95% CI, 0.57–0.73; P<.001), consistent with a median time to subsequent therapy of 6 years in the apalutamide group. Time to distant metastases improved by 32% (HR, 0.68; 95% CI, 0.55–0.83; P<.001).

Testosterone recovery was also addressed directly, a practical concern for patients weighing perioperative hormonal therapy. Testosterone recovery to a level of at least 200 ng/dL was reached in 81.6% of patients in the apalutamide group and 83.0% in the placebo group. The median time to testosterone recovery from the end of the 12-month perioperative treatment period was 8.1 months with apalutamide plus ADT compared with 6.6 months with placebo plus ADT, a modest difference suggesting that perioperative apalutamide does not substantially delay testosterone recovery beyond the effects of ADT alone. The most notable treatment-related toxicity was skin rash, occurring in 33% of the apalutamide arm versus a much lower rate on placebo, consistent with the drug's known safety profile; fatigue rates were similar between arms. Grade 3 or 4 adverse events occurred in 39.6% of the apalutamide group versus 31.0% of the placebo group, with the difference driven primarily by rash.

Taken together, PROTEUS represents the largest study of its kind in this space and is likely to establish a new standard of care in HR-LPC. The benefit was consistent across metastasis-free survival, biochemical response, and time to next therapy, with a tolerability profile consistent with prior apalutamide studies. An ongoing substudy is comparing apalutamide plus ADT plus radical prostatectomy against prostatectomy alone, which should further clarify the role of surgery within this regimen.

TALAPRO-3: Talazoparib Adds Benefit in HRR-Altered Metastatic Disease

For patients with metastatic castration-sensitive prostate cancer (mCSPC) harboring homologous recombination repair (HRR) gene alterations, TALAPRO-3 tested whether adding a PARP inhibitor to androgen receptor pathway inhibition could delay progression.

This phase 3 trial randomized 599 patients (300 to talazoparib 0.5 mg daily plus enzalutamide 160 mg daily, 299 to placebo plus enzalutamide 160 mg daily). BRCA1/2 alterations were present in 35% of patients in each arm, with ATM, CDK12, and CHEK2 alterations comprising most of the remainder. The primary endpoint, investigator-assessed radiographic progression-free survival, showed a 52% reduction in the risk of progression or death with talazoparib plus enzalutamide (HR, 0.48; 95% CI, 0.36–0.65; P<.001). Median rPFS was not reached in the talazoparib arm versus 45.8 months with placebo plus enzalutamide, at a median follow-up of roughly 37.6 months.

The benefit held up across HRR-altered subgroups, though with expected variation in magnitude: a 63% risk reduction was seen in the BRCA1/2-mutated subgroup (HR, 0.37) and a 43% risk reduction in the non-BRCA1/2-mutated subgroup (HR, 0.57). Interim overall survival trended in favor of the combination (HR, 0.77; 95% CI, 0.56–1.04), though this endpoint remains immature. Two treatment-related deaths occurred in the talazoparib group (due to pancytopenia and worsening idiopathic pulmonary fibrosis).

Adverse events were more frequent with the addition of talazoparib, as expected with a PARP inhibitor, with anemia, fatigue, and neutropenia the most common. Grade 3 or 4 anemia occurred in 51% of patients in the talazoparib arm. Anemia typically emerged early, within the first 13 weeks of treatment, and about 43% of patients had grade 1–2 anemia even before starting therapy. Importantly, median treatment duration was similar regardless of whether patients experienced grade 3–4 anemia (34.2 months) or did not (35.9 months), suggesting that with appropriate dose reduction and supportive care, most patients were able to remain on treatment. Only 5% of patients permanently discontinued talazoparib because of anemia.

These results support talazoparib plus enzalutamide as a treatment option for HRR-altered mCSPC, and further reinforce the need for comprehensive germline and somatic genomic testing at the time metastatic disease is diagnosed, allowing treatment selection to be guided by tumor biology rather than clinical features alone. 

A-DREAM: Can Some Patients Take a Break From ADT?

A question that comes up often in clinic is what to do with a patient who is responding exceptionally well to androgen receptor pathway inhibitor therapy. The A-DREAM trial (Alliance A032101) was designed to test whether treatment interruption is feasible in this specific scenario.

This single-arm phase 2 study enrolled 79 patients with mCSPC (78 eligible) who had been on testosterone suppression for 540–750 days and on an androgen receptor pathway inhibitor for at least 360 days, with a PSA below 0.2 ng/mL that was stable or falling. Both testosterone suppression and the androgen receptor pathway inhibitor were interrupted, with patients monitored via PSA every three months, imaging every six months, and quality-of-life questionnaires every six months. Treatment resumption was triggered by a PSA above 5 ng/mL, radiographic progression, or symptoms.

Notably, this was a higher-risk population than might be expected for a treatment-holiday study: median PSA at diagnosis was 19 ng/mL (range 5–6,759), 35% had high-volume disease, 40% had never received local therapy, and 71% had not received radiation to metastatic sites.

The primary endpoint, the proportion of patients remaining treatment-free with testosterone recovery to at least 150 ng/dL at 18 months, was met: 41% (32/78) of patients achieved this (80% CI, 33.5–48.9%; one-sided P=.025). Overall, 67% (52/78) of patients recovered their testosterone during follow-up, and 58% (45/78) remained treatment-free at 18 months. At a median follow-up of 21.2 months, 35% (27/78) resumed initial testosterone suppression plus ARPI.

Although encouraging, A-DREAM should not yet change routine clinical practice. The study was single-arm with relatively short follow-up, and longer-term outcomes are needed before treatment interruption can be recommended outside carefully selected patients or clinical trials. Nevertheless, these findings provide proof of concept that a subset of exceptional responders may be able to enjoy meaningful periods off therapy while maintaining disease control.

For Patients 

For men with high-risk prostate cancer being considered for surgery, the PROTEUS trial shows that adding a course of hormonal therapy with apalutamide before and after surgery can improve how completely the cancer responds and can delay its return, with side effects that are generally manageable and testosterone levels that recover on a similar timeline whether or not this therapy is used. 

For men with metastatic prostate cancer whose tumor testing reveals specific gene changes (called HRR alterations, including BRCA1/2), the TALAPRO-3 trial found that adding a PARP inhibitor called talazoparib to standard hormonal therapy meaningfully delayed cancer progression, most notably in those with BRCA1/2 changes. The most common side effect was anemia, which was manageable in most patients with dose adjustments. 

For men who have had an excellent, sustained response to hormonal therapy for metastatic disease, the A-DREAM study suggests that a supervised break from treatment may be possible for some patients, allowing testosterone levels and quality of life to recover for a meaningful period before treatment needs to resume. This approach requires close monitoring and is not appropriate for everyone, so it should only be considered in partnership with an oncology team.

Looking Ahead

Collectively, these studies highlight the evolving direction of prostate cancer care. Treatment intensification continues to improve outcomes for patients with biologically aggressive localized and metastatic disease, while emerging evidence suggests that carefully selected patients with exceptional responses may eventually benefit from treatment de-escalation. As genomic testing, advanced imaging, and individualized risk assessment become increasingly integrated into routine practice, management decisions are likely to become progressively more personalized, balancing disease control with long-term quality of life.

About the Author

Dalia Hammoud, MD, is Associate Professor of Medicine in the Division of Hematology/Oncology at Ochsner LSU Health Shreveport. She is a board-certified medical oncologist whose clinical practice spans the full spectrum of solid tumors, with particular expertise and academic interest in genitourinary malignancies, including prostate, bladder, and kidney cancers. She is actively involved in clinical research, medical education, and the translation of emerging evidence into evidence-based, patient-centered cancer care.

References 

1. Taplin ME, Gleave M, Shore ND, et al. Perioperative (neoadjuvant and adjuvant) apalutamide + ADT vs placebo + ADT with radical prostatectomy in high-risk localized or locally advanced prostate cancer: final analysis of the PROTEUS phase 3 study. Presented at: 2026 ASCO Annual Meeting. 

2. Agarwal N, Matsubara N, Azad AA, et al. TALAPRO-3: phase 3 study of talazoparib plus enzalutamide versus placebo plus enzalutamide for the treatment of patients with metastatic castration-sensitive prostate cancer harboring homologous recombination repair gene alterations. Presented at: 2026 ASCO Annual Meeting. 

3. Choudhury AD, Ballman K, Reimers MA, et al. A phase 2 trial of androgen deprivation therapy interruption in patients responding exceptionally to androgen receptor pathway inhibitor in metastatic hormone-sensitive prostate cancer: A-DREAM (Alliance A032101). Abstract 5004. Presented at: 2026 ASCO Annual Meeting.

4. Taplin ME, Gleave M, Shore ND, et al. Perioperative Apalutamide in High-Risk Localized Prostate Cancer. N Engl J Med. 2026. 

5. Agarwal N, Matsubara N, Azad AA, et al. PARP and Androgen-Signaling Inhibition plus ADT in Metastatic Prostate Cancer. N Engl J Med. 2026