PSMA-PET-CT May Let Half of High-Risk Men Skip Prostate Biopsy — What the Phase 3 Data Show

Why Prostate Biopsy Remains a Problem Worth Solving

Prostate biopsy is not a benign procedure. It carries meaningful risks — infection, bleeding, pain, and in rare cases sepsis — and generates anxiety disproportionate to what it often finds. Most critically, it regularly detects cancers that will never harm the patient: low-grade, slow-growing tumours that are better managed by active surveillance than treatment, but which nevertheless trigger a diagnostic cascade of further imaging, urologist visits, and often unnecessary intervention.

The challenge in prostate cancer diagnosis has never been finding prostate cancer — it is finding the right prostate cancer. Identifying the aggressive, clinically significant tumours that need treatment while sparing men with indolent disease (and disease-free men) from the physical and psychological burden of biopsy is the central unresolved problem in the field.

MRI has already improved this considerably. Multiparametric MRI, reported using the five-point PI-RADS scoring system, can stratify men by risk before biopsy and has reduced unnecessary procedures in men with low-risk scores. But MRI has limitations: a meaningful proportion of high-risk men have non-suspicious or equivocal MRI findings (PI-RADS 1–3), leaving clinicians uncertain whether to biopsy or observe. That is precisely the gap this trial was designed to address.

What Is PSMA-PET-CT and Why Does It Image Prostate Cancer So Well?

Prostate-specific membrane antigen (PSMA) is a transmembrane protein overexpressed on prostate cancer cells — typically 100 to 1,000 times more than on normal prostate tissue. Radiolabelled PSMA-targeting ligands, when injected intravenously, accumulate at PSMA-expressing sites and emit positron signals detectable by PET scanners. Combined with CT for anatomical localisation, the result is a highly sensitive and specific map of prostate cancer activity throughout the body.

PSMA-PET-CT is already well-established in oncology. The FDA has approved two PSMA-targeting radiotracers for prostate cancer imaging: gallium-68 PSMA-11 (Illuccix, Locametz) and fluorine-18 piflufolastat (Pylarify). Their primary approved indications are staging of high-risk prostate cancer before surgery and detecting biochemical recurrence after treatment — settings where their superiority over conventional imaging (bone scan, CT) is well-documented.

What is new — and what this trial directly tests — is using PSMA-PET earlier in the diagnostic pathway, before histological confirmation, to decide whether a biopsy is needed at all.

The Trial: How It Was Designed

The study enrolled 660 men across seven Australian hospitals — all with elevated PSA warranting clinical concern (median PSA 5.2 ng/mL) but with non-suspicious or equivocal MRI findings (equivalent to PI-RADS 1–3), meaning their MRI did not clearly identify a biopsy target. This is a clinically common and genuinely uncertain group: the MRI is not reassuring, but it is not convincingly abnormal either.

Participants were randomly assigned 1:1 to one of two arms:

In the experimental arm, the PRIMARY score determined the next step:

• PRIMARY score 1–2 (negative): No biopsy. Patient entered PSA surveillance with 2-year follow-up.
• PRIMARY score 3–5 (positive): Targeted transperineal biopsy guided by both PSMA-PET-CT and MRI targets, within 3 months.

What the PRIMARY Score Is

The PRIMARY score is a standardised five-point reporting system for PSMA-PET scans in the prostate diagnosis setting — the PSMA-PET equivalent of PI-RADS for MRI. Score 1 indicates no uptake suspicious for prostate cancer; score 5 indicates clearly positive. The use of a standardised, pre-specified scoring system was a key methodological strength, as it reduced interpretive variability between the seven participating sites.

The trial was designed as a noninferiority study — the question was not whether PSMA-PET detects more cancer than biopsy, but whether it detects clinically significant cancer at a rate no more than 10 percentage points lower than systematic biopsy. This is the appropriate design when the goal is to spare patients a procedure while preserving adequate clinical safety.

The Results: What the Numbers Mean

The headline finding is the 49% biopsy avoidance rate — nearly half of all men assigned to PSMA-PET-CT were deemed PRIMARY score 1 or 2 and avoided a biopsy entirely. For clinicians and patients, this is the most immediately meaningful number.

The noninferiority analysis focused on clinically significant prostate cancer detection. In the experimental arm, 12% of all randomised patients (39 of 331) were diagnosed with clinically significant prostate cancer. In the control (biopsy) arm, the figure was nearly 16% (51 of 329). The absolute difference was −3.7 percentage points, with a 95% confidence interval of −8.9 to 1.5 percentage points, entirely within the prespecified 10-percentage-point noninferiority margin. The p-value for noninferiority was 0.0093, confirming statistical significance.

Two findings beyond the headline deserve clinical attention:

The overdiagnosis reduction is striking. Clinically insignificant cancer — the slow-growing, low-grade tumours most appropriately managed by observation rather than treatment — was diagnosed in 14% of the PSMA-PET arm versus 32% of the biopsy arm (p < 0.0001). This near-halving of insignificant cancer diagnoses is not a minor secondary finding. Overdiagnosis of low-grade prostate cancer drives substantial overtreatment, with attendant harms including urinary incontinence, erectile dysfunction, and the psychological burden of a cancer diagnosis that was never going to cause harm.

The PSMA-PET strategy directed biopsy more efficiently. Among all randomised patients, 42% of those in the control arm had no cancer identified at biopsy — meaning their biopsy found nothing. In the experimental arm, only 22% had no cancer identified. The imaging approach concentrated biopsy on the men most likely to actually have clinically significant disease.

"This is a landmark study and one of the more encouraging developments in prostate cancer diagnosis. It's an elegant use of imaging to spare men a procedure many of them never needed."

— Wayne Brisbane, MD, University of California, Los Angeles

The Expert Debate: Is It Ready for the Clinic?

Brisbane's enthusiasm was qualified. He described PSMA-PET-CT as not yet ready for prime time, citing two concerns that any clinician or patient should understand before drawing conclusions from this trial.

First, follow-up data on patients who skipped biopsy are still maturing. The trial's primary endpoint was cancer detection at the point of randomisation, not long-term outcomes. Men who had a negative PSMA-PET and avoided biopsy remain under PSA surveillance, with 2-year follow-up ongoing. We do not yet know how many of those men will be diagnosed with significant cancer on subsequent surveillance — and that number will be the definitive test of whether the strategy is safe.

Second, tracer generalisability remains unresolved. The trial used gallium-68 PSMA-11 at expert Australian centres. In clinical practice across the United States, fluorine-18-labelled PSMA tracers (particularly piflufolastat) are now more widely used. The imaging characteristics differ somewhat between tracers, and the PRIMARY scoring system was developed specifically for gallium-68 PSMA-11. Whether the trial results transfer to other PSMA tracers in community imaging centres — not just expert academic sites — requires direct validation.

In an accompanying editorial in The Lancet Oncology, Daniel Spratt, MD, of Case Comprehensive Cancer Center, called the findings "promising" while cautioning that they "do not yet prove" a negative PSMA-PET can safely rule out clinically significant disease. Spratt argued that the follow-up of patients who avoided biopsy "should be viewed not as a secondary embellishment but as central to whether the strategy is safe."

What This Means If You Are Facing a Prostate Biopsy Decision

If your oncologist or urologist has raised the possibility of a prostate biopsy because of an elevated PSA, this trial is relevant but does not yet change what you should do. Here is how to think about it:

If your MRI is clearly abnormal (PI-RADS 4 or 5): This trial enrolled men with non-suspicious or equivocal MRI. If your MRI has already identified a suspicious lesion, the rationale for biopsy is different and this study does not apply to your situation.

If your MRI is negative or equivocal (PI-RADS 1–3) and your PSA is elevated: This trial is directly relevant to your scenario. A discussion with your urologist about whether PSMA-PET-CT is available and appropriate for your workup is reasonable — but be aware that the longer-term follow-up data on safety are still maturing.

Ask your doctor specifically:

• Is PSMA-PET-CT available at this centre, and which tracer is used?
• Would my PSA level and MRI findings make me a candidate for the imaging-first approach?
• What would happen if the PSMA-PET is negative — active surveillance or biopsy anyway?
• Is this centre following the PRIMARY scoring protocol used in the trial?

Men interested in participating in clinical trials studying PSMA-PET-guided diagnosis or novel diagnostic approaches can explore eligibility through KCLG Medical's patient pathway or ClinicalTrials.gov.

What This Means for Clinical Trial Design

From a clinical research perspective, the Lancet Oncology PSMA-PET trial is a methodologically instructive study in several respects.

The noninferiority design was the correct choice here — it is the only design that can formally support a strategy of doing less than the standard of care. A superiority design testing whether PSMA-PET detects more cancer than biopsy would have been the wrong question entirely. The 10-percentage-point noninferiority margin was pre-specified and clinically justified — small enough to be meaningful, large enough to be achievable given the expected population effect size.

The use of the PRIMARY score as a pre-specified, standardised, masked assessment tool is also exemplary. In diagnostic trials, reader variability is a major source of bias. By using independent reviewers masked to MRI and clinical information, and applying a validated five-point ordinal system, the trial minimises the risk that the imaging interpretation was influenced by knowledge of clinical risk.

The outstanding limitation — insufficient follow-up on the biopsy-avoided cohort — is a genuine gap that future research must address. Diagnostic trial design in oncology increasingly requires long-term outcome data, not just detection rate comparisons. Regulatory agencies and guideline bodies will require that gap to be filled before PSMA-PET can be formally recommended as a biopsy-replacement strategy.

For sponsors interested in diagnostic oncology trials, or in radioligand-related research across the PSMA pathway, KCLG Medical's research capabilities in oncology and radiology biomarker integration are outlined in our services section. See also our broader overview of radioligand therapy in oncology 2026.

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